ChapterPDF Available

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents Against Root Pathogens

April 2008
Mycorrhiza

April 2008

In book: Mycorrhiza (pp.281-307)
Edition: 2008
Chapter: Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents Against Root Pathogens
Publisher: Springer-Verlag Berlin Heidelberg
Editors: A. Varma

Authors:

Shwet Kamal

Directorate of Mushroom Research

Show all 5 authorsHide

In nature, production of disease-free plants with enhanced yield and compounds of therapeutic value can be mediated through rhizospheric microorganisms. There are increasing environmental concerns over the widespread use of biocontrol measures in general, and, alternatively, more sustainable methods of disease control are now being sought. Plant diseases caused by root pathogens need to be controlled in order to maintain the quality and abundance of food, feed and fiber, the prime necessities of life. Different approaches are used for prevention and control of these root pathogens. Among these alternatives are those referred to as biological control; the most obvious and apparently biological control is a potent means of reducing the damage caused by plant pathogens. The potential agents for biocontrol activity are rhizosphere-competent fungi and bacteria which, in addition to their antagonistic activity, are capable of inducing growth responses by either controlling minor pathogens or by producing growth-stimulating factors. A variety of biological controls are available for use, but further development and effective adoption requires a greater understanding of the complex interactions among plants, people, and the environment. This article emphasizes: (1) information about mycorrhiza and root endophytes, (2) various definitions and key mechanisms of biocontrol, and (3) the relationships between microbial diversity and biological control.

Content uploaded by Shwet Kamal

Content may be subject to copyright.

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes

as Biocontrol Agents Against Root Pathogens

S. Tripathi, S. Kamal, I. Sheramati, R. Oelmuller, and A. Varma(*ü )

1 Introduction

In nature, production of disease-free plants with enhanced yield and compounds of thera-

peutic value can be mediated through rhizospheric microorganisms. There are increasing

environmental concerns over the widespread use of biocontrol measures in general, and,

alternatively, more sustainable methods of disease control are now being sought. Plant

diseases caused by root pathogens need to be controlled in order to maintain the quality

and abundance of food, feed and fiber, the prime necessities of life. Different approaches

are used for prevention and control of these root pathogens. Among these alternatives are

those referred to as biological control; the most obvious and apparently biological control

is a potent means of reducing the damage caused by plant pathogens. The potential

agents for biocontrol activity are rhizosphere-competent fungi and bacteria which, in

addition to their antagonistic activity, are capable of inducing growth responses by either

controlling minor pathogens or by producing growth-stimulating factors.

A variety of biological controls are available for use, but further development and

effective adoption requires a greater understanding of the complex interactions among

plants, people, and the environment. This article emphasizes: (1) information about

mycorrhiza and root endophytes, (2) various definitions and key mechanisms of bio-

control, and (3) the relationships between microbial diversity and biological control.

2 Endophytes

2.1 Definition of an Endophyte

The term endophyte was introduced by De Bary (1866) and was initially applied to

any organism found within a plant. Petrini (1991) used the term endophyte to mean

all organisms inhabiting plant organs that at some time in their life can colonize

[Au1][Au1]

A. Varma

Amity Institute of Microbial Sciences, Amity University Uttar Pradesh, Block- A,

Sec-125, Express Highway, Noida 201 303, Uttar Pradesh, India

e-mail: ajitvarma@aihmr.amity.edu

A. Varma (ed.) Mycorrhiza, 281

Varma_Ch14.indd 281Varma_Ch14.indd 281 4/23/2008 7:26:25 AM4/23/2008 7:26:25 AM

Uncorrected Proof

282 S. Tripathi et al.

internal plant tissues without causing apparent harm to the host. This has been the

most widely used definition of endophytes and also includes the organisms that

have a more or less lengthy epiphytic phase and also latent pathogens (Schulz et al.

1998; Petrini 1991).

Studies on the endophyte composition in different hosts have identified organ-

isms with varying roles within their hosts. By analyzing the different levels of

endophytic association, Wilson (1995) stated that “endophytes are fungi or bacteria

which, for all or part of their life cycle, invade the tissues of living plants and cause

unapparent and asymptomatic infections entirely within plant tissues but causes no

symptoms of the disease.” The same organism may also be described as a saprobe

or pathogen at other times (Boddy and Griffith 1989).

2.2 Role of Endophytes

Endophytes previously defined as mutualists are closely related to virulent pathogens

but have limited pathogenicity, and have probably evolved directly from plant patho-

genic fungi (Carroll 1988). The mutualistic symbiosis includes the lack of destruction

of most cells or tissues, nutrient and chemical cycling between the fungus and hosts,

enhanced longevity and photosynthetic capacity of cell and tissue under the influence

of infection, enhanced survival of fungus, and a tendency towards greater host specifi-

city than is seen in necrotrophic infections (Lewis 1973).

In the grasses and other plant hosts, endophytes have also been shown to enhance

plant growth, reduce infection by nematodes, increase stress tolerance and increase

nitrogen uptake in nitrogen deficit soils (Bacon 1993; Bultman and Murphy 2000;

Clay 1987, 1990; Gasoni and Stegman De Gurfinkel 1997; Kimmons 1990; Varma

et al. 1999; Jordaan et al. 2006). Several reviews are available on secondary metabolite

production by endophytes (Miller 1986; Clay 1991; Tejesvi et al. 2006). Endophytes

in culture can produce biologically active compounds (Brunner and Petrini 1992)

including several alkaloids, paxilline, lolitrems and tertraenone steroids (Dahlman et al.

1991), antibiotics (Fisher et al. 1984a, 1984b) and plant growth promoting factors

(Petrini et al. 1992). Endophytes are increasingly being identified as a group of

organisms capable of providing a source of secondary metabolites for the use in

biotechnology and agriculture (Bills and Polishook 1992).

2.3 Modes of Endophytic Colonization

The colonization of plant tissues by endophytes, plant pathogens and mycorrhizae

involves several steps involving host recognition, spore germination, penetration of

the epidermis and tissue colonization (Petrini 1991, 1996). The inoculum source of

fungal endophytes is widely considered to be the airborne spores, and also by seed

transmission and transmission of propagules by insect vectors (Petrini 1991). In

[Au2][Au2]

Varma_Ch14.indd 282Varma_Ch14.indd 282 4/23/2008 7:26:25 AM4/23/2008 7:26:25 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 283

terms of mechanical and enzymatic elements of penetration by endophytic fungi, it

can be assumed that endophytes adopt the same strategy for penetration of host tis-

sue as pathogens (Petrini et al. 1992). Fungi can invade plant tissues by direct

cuticular penetration, via appressoria formed on the cuticle, after which penetration

occurs through the cuticle and epidermal cell wall, or via natural openings like sto-

mata (O’Donnell and Dickinson 1980; Kulik 1988). Following the penetration, the

infection may be intercellular or intracellular and may be limited to one cell or in a

limited area around the penetration site. Limited cytological works on nonclavicipi-

taceous endophytes have shown that the infection of these endophytes in host plants

may be inter- or intracellular and often localized in single cells (Stone 1988; Suske

and Acker 1989).

3 Mycorrhizal Fungi

The roots of most plant species live associated with certain soil fungi. This symbi-

otic establishment is known as mycorrhiza (Smith and Read 1997; Marschner and

Rengel 2007). Mycorrhizal functions include improvement of plant establishment,

enhancement of nutrient uptake, protection against cultural and environmental

stresses, and the improvement of soil structure (Barea 1997).

All types of ecological situations can be suitable for mycorrhizal symbiosis.

Most plant species are able of forming this symbiosis naturally; the most common

type involved in the normal cropping systems is the arbuscular mycorrhizal (AM)

type (Smith and Read 1997). A very common group of soilborne fungal order,

Glomales in the Zygomycetes, has this AM fungi (Morton and Redecker 2001).

Recent developments in molecular biology based on PCR-based approaches are

being applied to the genetic characterization of AM fungi (Sanders et al. 1996). The

analysis of rRNA sequences in last few years has demonstrated the polymorphism

of these genes in AM fungi, particularly those corresponding to the small ribosomal

subunit 18S, thus allowing for detailed diversity and phylogenetic studies (Redecker

et al. 2000; Daniell et al. 2001). Novel techniques for microbial molecular ecology

studies, like PCR-SSCP and PCR-TGGE, are being adopted for the characteriza-

tion of different ecotypes of AM fungi, both in soil and in roots (Pawlowska and

Taylor 2004).

3.1 Taxonomy of AM Fungi

Arbuscular mycorrhizal (AM) fungi form a widespread and ecologically important

symbiosis with plants in the land ecosystem. The phylogeny of the largest presently

accepted genus, Glomus, of the monogeneric family Glomaceae (Glomales; AM fungi)

has been analyzed. Phylogenetic trees were computed from nearly full-length SSU

Varma_Ch14.indd 283Varma_Ch14.indd 283 4/23/2008 7:26:25 AM4/23/2008 7:26:25 AM

Uncorrected Proof

284 S. Tripathi et al.

rRNA gene sequences of 30 isolates, and show that “Glomus” is not monophyletic.

Even after the very recent separation of Archaeospora and Paraglomus from “Glomus”

the genus further separates into two suprageneric clades. One of them diverges further

into two subclades, differing by phylogenetic distances equivalent to family level. The

other, comprising Glomus versiforme, G. spurcum and a species morphologically simi-

lar to G. etunicatum, is not closely related to the Glomaceae, but clusters together with

the Acaulosporaceae and Gigasporaceae in a monophyletic clade. Based on the molecu-

lar evidence, a new family, separate from the Glomaceae, is required to accommodate

this group of organisms, and initially named Diversisporaceae fam. Ined (Fig. 1). The

current taxonomic concept of the recently erected family Archaeosporaceae also

requires future emendation, because Geosiphon pyriformis (Geosiphonaceae) renders

Archaeospora, the sole genus formally included in this family, paraphyletic. The sub-

orders Gigasporineae and Glominaeae are not congruent with the natural phylogeny of

the AM fungi (Schüßler et al. 2001; Walker and Schüßler 2004).

3.2 Functions of AM Fungi

During the process of AM formation (Giovannetti 2000; Avio et al. 2006; Bedini et

al. 2007), in which the plant “accepts” the fungal colonization without any signifi-

cant rejection reaction (Dumas-Gaudot et al. 2000), a series of root–fungus interac-

tions give way to the integration of both organisms. The establishment of the

symbiosis is the result of a continuous molecular “dialogue” between plant and

fungus, as exerted through the exchange of both recognition and acceptance signals

(Vierheilig and Piché 2002). The result of this dialogue finally depends on the

Glomeraceae

( -group A)

Glomus

Glomerales

Glomeraceae

(-group B)

Glomus

Basidiomycetes

Ascomycetes

Piriformospora indica

Verma et al

89 84

0.01

State-of- Art

Fig. 1 Proposed generalised taxonomic structure of the AM and related fungi (Glomeromycota),

based on SSU rRNA gene sequences. Thick lines delineate bootstrap support above 95%, lower

values are given on the branches. The four-order structure for the phylogenetic position of

P. indica (after Schüßler et al. 2001; Varma et al. 2001)

Varma_Ch14.indd 284Varma_Ch14.indd 284 4/23/2008 7:26:25 AM4/23/2008 7:26:25 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 285

genome expression of both partners (Gianinazzi-Pearson et al. 1996; Bestel-Corre

et al. 2004; Franken and Requena 2001; Kuster et al. 2007).

After the biotrophic colonization of root cortex, these AM fungi develop an external

mycelium which serves as a bridge connecting the root with the surrounding soil micro-

habitats. Such mycorrhizal (fungal–root) symbiosis is critical in nutrient cycling in soil–

plant systems (Smith and Read 1997). In cooperation with other soil organisms, the

external AM fungal mycelium forms water-stable aggregates necessary for good soil

tilth. The AM symbiotic association helps in the improvement of plant health through

increased protection against biotic and abiotic stresses (Miller and Jastrow 2000;

Requena et al. 2001; Requena et al. 2007; Ocon et al. 2007). Some relevant papers

dealing with interaction of mycorrhizal fungi with root pathogens are listed in Table 1.

3.3 Piriformospora indica: a Novel Mycorrhiza-like Fungus

The scientists from the School of Life Sciences, Jawaharlal Nehru University, New

Delhi, have screened a novel endophytic root-colonizing fungus Piriformospora

indica for the first time, which mimics the capabilities of a typical arbuscular myc-

orrhizal fungus. Based on the anatomical and genomic studies, P. indica has been

attributed to highly evolved Hymenomycetes (Basidiomycetes). This fungus has

been patented (Varma A & Franken P, 1997) at theEuropean Patent Office,

(continued)

Table 1 Relevant publications

Title Reference

Isolation from the Sorghum bicolor mycorrhizosphere of a bacterium

compatible with arbuscular mycorrhiza development and antagonistic

towards soilborne fungal pathogens

Budi et al. (1999)

Arbuscular mycorrhizas: physiology and function Linderman (2000)

What do root pathogens see in mycorrhizas? James (2001

The defense response elicited by the pathogen Rhizoctonia solani is sup-

pressed by colonization of the AM-fungus Glomus intraradices

Guenoune (2001)

Insect pathogens as biological control agents: do they have a future? Lacey et al. (2001)

Microbial populations responsible for specific soil suppressiveness to

plant pathogens

Weller et al. (2002)

Effects of arbuscular mycorrhizal fungi and a non-pathogenic Fusarium

oxysporum on Meloidogyne incognita infestation of tomato

Diedhiou et al.

(2003)

A review of fungal antagonists of powdery mildews and their potential as

biocontrol agents

Kiss (2003)

Assessment of arbuscular mycorrhizal fungi as potential biocontrol

agents for Poa annua L. in fine turf

Gange et al. (2004)

Microbial diversity in soil: selection of microbial populations by plant

and soil type and implications for disease suppressiveness

Garbeva et al.

(2004)

The potential role of arbuscular mycorrhizal (AM) fungi in the biopro-

tection of plants against soil-borne pathogens in organic and/or other

sustainable farming systems

Harrier and Watson

(2004)

Varma_Ch14.indd 285Varma_Ch14.indd 285 4/23/2008 7:26:28 AM4/23/2008 7:26:28 AM

Uncorrected Proof

286 S. Tripathi et al.

Müenchen, Germany (Patent No. 97121440.8–2105, Nov. 1998/ WO 99/ 29177,

June 17, 1999) and the culture has been deposited at Braunsweich, Germany (DMS

No. 11827). The 18 s rDNA fragment has been deposited in GenBank, Bethesda,

USA. Like arbuscular mycorrhizal (AM) fungi, P. indica functions as bioregulator,

biofertilizer and bioprotector, overcomes the water stress (dehydration), delays the

wilting of the leaves, and prolongs aging of callus tissues. Interestingly, the host

spectrum of P. indica is very much like AM fungi and can colonize the roots and

improve the health, vigor and survival of a wide range of mono- and dicotyledon

plants. This fungus mediates uptake of phosphorus from the substratum and its

translocation to the host by an energy-dependent active process. It serves as a strong

agent for biological hardening of tissue culture-raised plants, protecting them from

“transplantation shock”, rendering almost 100% survivals on the hosts tested. This

fungus is also a potential biological agent against potent root pathogens. Thus, it

displays immense potential to be utilized as biological tool for plant promotion,

protection from pests, and for relieving stress conditions such as those caused due

to acidity, desiccation and heavy metal toxicity (Sherameti et al. 2005; Shahollari

Arbuscular mycorrhizal fungi reduce development of pea root-rot caused

by Aphanomyces euteiches using oospores as pathogen inoculum

Thygesen et al.

(2004)

Use of plant growth-promoting bacteria for biocontrol of plant diseases:

principles, mechanisms of action, and future prospects

Compant et al.

(2005)

Moderate drought influences the effect of arbuscular mycorrhizal fungi

as biocontrol agents against Verticillium-induced wilt in pepper

Garmendia et al.

(2005)

The endophytic fungus Piriformospora indica reprograms barley to salt

stress tolerance, disease resistance and higher yield

Waller et al. (2005)

Involvement of jasmonic acid/ethylene signaling pathway in the systemic

resistance induced in cucumber by Trichoderma asperellum T203

Shoresh et al. (2005)

Biological control of root-rot disease complex of chickpea by AM fungi Siddiqui et al.

(2006)

Colonization by the arbuscular mycorrhizal fungus Glomus versi-

forme induces a defense response against the root-knot nematode

Meloidogyne incognita in the grapevine (Vitis amurensis Rupr.),

which includes transcriptional activation of the class III chitinase

gene VCH3

Li et al. (2006)

Biological control of plant pathogens Pal et al. (2006)

Root exudates of mycorrhizal tomato plants exhibit a different effect on

microconidia germination of Fusarium oxysporum f. sp. lycopersici

than root exudates from non-mycorrhizal tomato plants

Scheffknecht et al.

(2006)

Biological control of plant diseases Chincholkar and

Mukerji (2007)

Mycorrhizae in the integrated pest and disease management Mukerji and Ciancio

(2007)

Performance of the biocontrol fungus Piriformospora indica on wheat

under greenhouse and field conditions

Serfling et al. (2007)

Plant biology: jasmonate perception machines Farmer (2007)

Table 1 (continued)

Title Reference

Varma_Ch14.indd 286Varma_Ch14.indd 286 4/23/2008 7:26:28 AM4/23/2008 7:26:28 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 287

et al. 2005; Waller et al. 2005; Serfling et al. 2007). Multifunctional aspect of the

fungus is depicted in Fig. 2.

4 Plant Growth-promoting Rhizobacteria (PGPRs)

The beneficial root-colonizing rhizosphere bacteria, the plant growth-promoting

rhizobacteria (PGPRs), are defined by three intrinsic characteristics (1) they have

to survive and multiply in microhabitats associated to root surface, in competition

with native microbiota, at least for the time needed to express their plant promotion

activities, (2) they must have the ability for root colonization, and (3) they must

have the ability for plant growth promotion (Kloepper 1994). The PGPRs are

known to carry out many important ecosystem processes, such as those involved in

the biological control of plant pathogens, nutrient cycling and seedling establish-

ment (Lemanceau and Alabouvette 1993; Glick 1995; Broek and Vanderleyden

1995; Probanza et al. 2002; Baldock et al. 2004). Many bacterial taxa include

PGPR strains. Pseudomonas and Bacillus are the most common described genera

as possessing species with PGPRs ability, and some strains from these and other

genera are being used as seed inoculants (Bertrand et al. 2001; Ziedan 2006).

Azospirillum sp. is considered PGPR (Bashan 1999; Bashan and Gonzalez 1999;

El Zemrany et al. 2006) and used as seed inoculants under field conditions

(Dobbelaere et al. 2001). The main activity of these bacteria is associated to the

production of auxin-type phytohormones (Dobbelaere et al. 1999). The production

and significance of auxins have been investigated at a molecular level (van de

Broek et al. 1999; Lambrecht et al. 2000). The molecular bases of the biocontrol

ability of these rhizobacteria are currently being investigated, and systemic-induced

Plant Promoter

Plant Protector

Immuno - modulator

Enlarges Nuclear

Material

Promotes Secondary

Metabolite

Resistance Against

Heavy Metals & Drought

Biofertilizer Bio - herbicide

Piriformospora

indica

Fig. 2 The multifunctional aspect of Piriformospora indica

Varma_Ch14.indd 287Varma_Ch14.indd 287 4/23/2008 7:26:28 AM4/23/2008 7:26:28 AM

Uncorrected Proof

288 S. Tripathi et al.

resistance has been argued as a mechanism of disease suppression by endophytes

(Duijff et al. 1998; Ramarathnam and Dilantha 2006) or other PGPRs (Defago and

Keel 1995; Chin-A-Woeng et al. 2001; Barka et al. 2005).

5 Biological Control

The term “biological control” has been used in different fields of biology. In plant

pathology, the term applies to the use of microbial antagonists to suppress diseases

as well as the use of host-specific pathogens to control weed populations. In both

fields, the organism that suppresses the pest or pathogen is referred to as the bio-

logical control agent (BCA).

5.1 Basics of Biocontrol

Biological control is the suppression of damaging activities of one organism by one

or more other organisms. This refers to the purposeful utilization of introduced or

resident living organisms, other than disease-resistant host plants, to suppress the

activities and populations of one or more plant pathogens. This may involve the use

of microbial inoculants to suppress a single type or class of plant diseases. Or, this

may involve managing soils to promote the combined activities of native soil- and

plant-associated organisms that contribute to general suppression. Finally, biologi-

cal control refers to the suppression of a single pathogen (or pest), by a single

antagonist in a single cropping system. With regards to plant diseases, suppression

can be accomplished in many ways (Pal and Gardener 2006).

5.2 Biocontrol Versus Chemical Control

The use of chemical pesticides and insecticides based on synthetic formulations

with a higher specificity towards their target organism has led to dramatic improve-

ments in the production of crop plants, provided a reliable supply of cheap food,

generally exhibited low overall toxicity and with little immediate impact on the

environment. But the long-term effects of these compounds have a detrimental

effect on soil fertility and development of resistance in pathogens. Excessive use of

these chemicals has an effect on food quality and environmental damage leading to

nonsustainability of farming. The need of the day is to develop sustainable, long-

term, and ecological- and environment-friendly alternatives to pesticides, which are

naturally occurring microbes provided by nature for ages but not utilized to their

full potential.

[Au3][Au3]

Varma_Ch14.indd 288Varma_Ch14.indd 288 4/23/2008 7:26:28 AM4/23/2008 7:26:28 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 289

The most obvious and apparently biological control is a potent means of reduc-

ing the damage caused by plant pathogens. The potential agents for biocontrol

activity are rhizosphere-competent fungi and bacteria which, in addition to their

antagonistic activity, are capable of inducing growth responses by either controlling

minor pathogens or by producing growth-stimulating factors.

6 Microbial Diversity and Disease Suppression

Plants are surrounded by diverse types of microbial organisms, which contribute to

biological control of plant diseases. Microbes contributing to the disease control

can be classified as competitive saprophytes, facultative plant symbionts and

facultative hyperparasites. These generally survive on dead plant material and are

able to colonize and express biocontrol activities while growing on plant tissues. A

few, like avirulent Fusarium oxysporum and binucleate Rhizoctonia-like fungi, are

phylogenetically very similar to plant pathogens, but lack active virulence determi-

nants for many of the plant hosts from which they can be recovered. Others, like

Pythium oligandrum are currently classified as distinct species. P. indica blocks the

mycelial development in Gaeumannomyces graminis and Fusarium sp. (Figs. 3 and 4).

However, most are phylogenetically distinct from pathogens and, most often; they

are subspecies variants of the same microbial groups. At the moment we do not

have knowledge for the mechanism and the Biomolecules involved for imparting

such prominent inhibitory impact.

Due to the ease with which they can be cultured, most biocontrol research has

focused on a limited number of bacterial (Bacillus, Burkholderia, Lysobacter,

Pantoea, Pseudomonas, and Streptomyces) and fungal (Ampelomyces,

Coniothyrium, Dactylella, Gliocladium, Paecilomyces and Trichoderma) genera.

Still, other microbes that are more recalcitrant to in vitro culturing have been

intensively studied. These include mycorrhizal fungi, e.g., Pisolithus and Glomus

spp. that can limit subsequent infections, and some hyperparasites of plant patho-

gens, e.g., Pasteuria penetrans, which attacks root-knot nematodes. Because

multiple infections can and do take place in field-grown plants, weakly virulent

pathogens can contribute to the suppression of more virulent pathogens, via the

induction of host defenses. Lastly, there are the many general micro- and meso-

fauna predators, such as protists, Collembola, mites, nematodes, annelids, and

insect larvae, whose activities can reduce pathogen biomass but may also facili-

tate infection and/or stimulate plant host defenses by virtue of their own herbivo-

rous activities.

While various epiphytes and endophytes may contribute to biological control,

the ubiquity of mycorrhizae deserves special consideration. Mycorrhizae are

formed as the result of mutualist symbioses between fungi and plants and occur on

most plant species. Because they are formed early in the development of the plants,

they represent nearly ubiquitous root colonists that assist plants with the uptake of

nutrients (especially phosphorus and micronutrients). The arbuscular mycorrhizal

Varma_Ch14.indd 289Varma_Ch14.indd 289 4/23/2008 7:26:28 AM4/23/2008 7:26:28 AM

Uncorrected Proof

290 S. Tripathi et al.

fungi (AM, also known as arbuscular mycorrhizal or endomycorrhizal fungi) are all

members of the zygomycota, and the current classification contains one order, the

Glomales, encompassing six genera into which 149 species have been classified

(Morton and Benny 1990; Garbewa et al. 2004; Mukerji and Ciancio 2007).

Arbuscular mycorrhizae involve aseptate fungi and are named for characteristic

structures like arbuscles and vesicles found in the root cortex. Arbuscules start to

form by repeated dichotomous branching of fungal hyphae approximately 2 days

after root penetration inside the root cortical cell. Arbuscules are believed to be the

site of communication between the host and the fungus. Vesicles are basically

hyphal swellings in the root cortex that contain lipids and cytoplasm and act as

storage organ of AM. These structures may present intra- and intercellular and can

often develop thick walls in older roots. These thick-walled structures may function

as propagules (Biermann and Linderman 1983). During colonization, AM fungi

can prevent root infections by reducing the access sites and stimulating host

defense. AM fungi have been found to reduce the incidence of root-knot nematodes

(Linderman 1994). Various mechanisms also allow AM fungi to increase a plant’s

stress tolerance. This includes the intricate network of fungal hyphae around the

roots which block pathogen infections. Inoculation of apple tree seedlings with the

P. indica P. indica P. indica

G. graminis G. graminis

Alternaria sp

P. indicaP. indica

Fusarium sp

P. indica

cde

Fig. 3 Interaction of P. indica with plant pathogens. a Gaeumannomyces graminis (front view).

b G. graminis (back view). c Alternaria sp. d P. indica (control). e Fusarium sp. (partially modi-

fied from Varma et al. 2001)

Varma_Ch14.indd 290Varma_Ch14.indd 290 4/23/2008 7:26:28 AM4/23/2008 7:26:28 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 291

AM fungi Glomus fasciculatum and G. macrocarpum suppressed apple replant disease

caused by phytotoxic myxomycetes (Catska 1994). AM fungi protect the host plant

against root-infecting pathogenic bacteria. The damage due to Pseudomonas syrin-

gae on tomato may be significantly reduced when the plants are well-colonized by

mycorrhizae (Garcia-Garrido and Ocampo 1989; Garcia-Garrido et al. 2000). The

mechanisms involved in these interactions include physical protection, chemical

interactions and indirect effects (Fitter and Garbaye 1994). The other mechanisms

employed by AM fungi to indirectly suppress plant pathogens include enhanced

nutrition to plants, morphological changes in the root by increased lignification,

changes in the chemical composition of the plant tissues like antifungal chitinase,

isoflavonoids, etc. (Morris and Ward 1992; Garcia-Garrido et al. 2000); alleviation

of abiotic stress, salinity stress (Rabie and Almadini 2005), and changes in the

microbial composition in the mycorrhizosphere (Linderman 1994). In contrast to

Control

Fusarium P. indica + Fusarium

Shoot f. wt. [%]

aab

100

120

140

160

180

200

100 300 0 100 300 mM NaCII

P. indica

Fig. 4 Impact of P. indica on salt-stress tolerance and root infections by F. culmorum. a Shoot fresh

weight of P. indica and control (noninfested) plants was determined in 5-week-old plants that had

been grown for the final 2 weeks in the presence of 100 or 300 mM NaCl, in hydroponic culture.

Data points are representative of three independent experiments. Error bars SD. b Plant phenotypes

demonstrating the protective potential of P. indica toward F. culmorum (Waller et al. 2005)

Varma_Ch14.indd 291Varma_Ch14.indd 291 4/23/2008 7:26:29 AM4/23/2008 7:26:29 AM

Uncorrected Proof

292 S. Tripathi et al.

AM fungi, ectomycorrhizae proliferate outside the root surface and form a sheath

around the root by the combination of mass of root and hyphae called a mantle.

Disease protection by ectomycorrhizal fungi may involve multiple mechanisms

including antibiosis, synthesis of fungistatic compounds by plant roots in response

to mycorrhizal infection and a physical barrier of the fungal mantle around the plant

root (Duchesne 1994; Garcia-Garrido et al. 2000). Ectomycorrhizal fungi like

Paxillus involutus effectively controlled root rot caused by Fusarium oxysporum

and Fusarium moniliforme in red pine. Inoculation of sand pine with Pisolithus

tinctorius, another ectomycorrhizal fungus, controlled disease caused by

Phytophthora cinnamomi (Ross and Marx 1972).

Since plant diseases may be suppressed by the activities of one or more plant-

associated microbes, attempts have been made to characterize the organisms involved

in biological control. Historically, this has been done primarily through isolation,

characterization, and application of individual organisms. By design, this approach

focuses on specific forms of disease suppression. Specific suppression results from

the activities of one or just a few microbial antagonists. This type of suppression is

thought to be occurring when inoculation of a biocontrol agent results in substantial

levels of disease suppressiveness. It may also occur in natural systems from time to

time. For example, the introduction of Pseudomonas fluorescens that produce the

antibiotic 2,4-diacetylphloroglucinol can result in the suppression of various soil

borne pathogens. However, specific agents must compete with other soil- and

root-associated microbes to survive, propagate, and express their antagonistic poten-

tial during those times when the targeted pathogens pose an active threat to plant

health. In contrast, general suppression is more frequently invoked to explain the

reduced incidence or severity of plant diseases because the activities of multiple

organisms can contribute to a reduction in disease pressure. High soil organic matter

supports a large and diverse mass of microbes resulting in the availability of fewer

ecological niches for which a pathogen competes. The extent of general suppression

will vary substantially depending on the quantity and quality of organic matter

present in a soil (Hoitink and Boehm 1999). Functional redundancy within different

microbial communities allows for rapid depletion of the available soil nutrient pool

under a large variety of conditions, before the pathogens can utilize them to proliferate

and cause disease. For example, diverse seed-colonizing bacteria can consume nutri-

ents that are released into the soil during germination, thereby suppressing pathogen

germination and growth (McKellar and Nelson 2003). Manipulation of agricultural

systems, through additions of composts, green manures and cover crops, is aimed at

in proving endogenous levels of general suppression (Hameeda et al. 2007).

7 Interactions for the Biological Control of Root Pathogens

Once the AM status has been established in plant roots, a reduced damage caused

by soilborne plant pathogens has been shown by several mechanisms suggested

to explain the enhancement of plant resistance/tolerance in mycorrhizal plants

Varma_Ch14.indd 292Varma_Ch14.indd 292 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 293

(Azcón-Aguilar and Barea 1992, 1996; Linderman 1994, 2000). The important

one is based on the microbial changes produced in the mycorrhizosphere (Mukerji et al.

1998; Giri et al. 2004). Some microbial shifts occur which result in microbial

equilibria and influence the growth and health of the plants. Although this

effect has not been assessed specifically as a mechanism for AM-associated

biological control, there are indications that such a mechanism can be involved

(Azcón-Aguilar and Barea 1992, 1996; Linderman 1994, 2000). In any case, it

has been demonstrated that such an effect is dependent on the AM fungus

involved, as well as the substrate and host plant (Azcón-Aguilar and Barea

1996; Linderman 2000).

Since specific PGPR antagonistic to root pathogens are being used as biological

control agents (Alabouvette et al. 1997), it has been proposed to exploit the prophy-

lactic ability of AM fungi in association with these antagonists (Azcón-Aguilar and

Barea 1996; Linderman 1994, 2000).

Several studies have demonstrated that microbial antagonists of fungal patho-

gens, either fungi or PGPRs, do not exert any antimicrobial effect against AM

fungi. This is a key point to exploit the possibilities of dual (AM fungi and PGPRs)

inoculation in plant defense against root pathogens.

7.1 Types of Interactions Contributing to Biological Control

The interactions with various organisms throughout their lifecycle affect plant

health in various ways. The mechanisms of biological control depend upon these

various ways that organisms interact. The mode of interaction is by means of direct

or indirect contact. The types of interactions were referred to as mutualism, proto-

cooperation, commensalism, neutralism, competition, parasitism, and predation

(Odum 1953). Since, both the plants and microbes are involved in the development

of plant diseases, the interactions leading to biological control occur at multiple

levels of scale.

Biological control is considered a net positive result on the plants arising from

a variety of specific and non-specific interactions (Pal and Gardener 2006). An

association between two or more species where both species derive benefit is

known as mutualism. It is an obligatory interaction which involves close physical

and biochemical contact, like those between plants and mycorrhizal fungi.

However, they are generally facultative and opportunistic. Rhizobium can reproduce

either in the soil or through their mutualistic association with legume plants. This

interaction can contribute to biological control, by fortifying the plant with

improved nutrition and/or by stimulating host defenses. Protocooperation is a

form of mutualism, but the involved organisms do not depend exclusively on each

other for survival. Since these are independent of any specific host, disease sup-

pression varies depending on environmental conditions. Further, commensalism

is a symbiotic interaction, where one organism benefits and the other is neither

harmed nor benefited. The plant-associated microbes are mostly assumed to be

Varma_Ch14.indd 293Varma_Ch14.indd 293 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

294 S. Tripathi et al.

commensals with regards to the host plant. Neutralism describes the interactions

when the population density of one species has absolutely no effect on the other.

With reference to biological control, an inability to associate the population

dynamics of pathogen with that of another organism would indicate neutralism.

In contrast, antagonism between organisms results in a negative outcome for one

or both. Competition within and between species results in decreased growth,

activity and/or fecundity of the interacting organisms. Biocontrol can occur when

nonpathogens compete with pathogens for nutrients in and around the host plant.

Direct interactions that benefit one population at the expense of another also

affect our understanding of biological control. Parasitism is a symbiosis in which

two phylogenetically unrelated organisms coexist over a prolonged period of

time. In this type of association, one organism, the parasite benefits and the other,

the host is harmed. The activities of various hyperparasites, i.e., agents that para-

sitize plant pathogens, can result in biocontrol. Lastly, predation refers to killing

of one organism by another for consumption and sustenance. The term has been

applied to the actions of microbes that consume pathogen biomass for sustenance.

Biological control results from all of these types of interactions, depending on the

environmental context within which they occur. Significant biological control, as

defined above, most generally arises from manipulating mutualisms between

microbes and their plant hosts or from manipulating antagonisms between

microbes and pathogens (Pal and Gardener 2006).

7.2 Mechanisms of Biological Control

Biological control can result from many different types of interactions between

organisms; the mechanisms operating in different experimental situations are to

be characterized. The pathogens are antagonized by the presence and activities of

other organisms in vicinity. Direct antagonism results from physical contact and/

or a high-degree of selectivity for the pathogen by the mechanisms expressed by

the BCAs. In such a scheme, hyperparasitism by obligate parasites of a plant

pathogen would be considered the most direct type of antagonism because the

activities of no other organism would be required to exert a suppressive effect.

In contrast, indirect antagonisms result from activities that do not involve sensing

or targeting a pathogen by the BCA(s). Antagonistic pathways are as depicted in

Table 2. Stimulation of plant host defense pathways by nonpathogenic BCAs is

the most indirect form of antagonism. The most effective BCAs studied to date

appear to antagonize pathogens using multiple mechanisms. For instance,

pseudomonad’s known to produce the antibiotic 2,4-diacetylphloroglucinol

(DAPG) may also induce host defenses (Iavicoli et al. 2003). Additionally,

DAPG-producers can aggressively colonize roots, a trait that might further con-

tribute to their ability to suppress pathogen activity in the rhizosphere of wheat

through competition for organic nutrients (Weller et al. 2002).

Varma_Ch14.indd 294Varma_Ch14.indd 294 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 295

7.2.1 Hyperparasites and Predation

In general, there are four major classes of hyperparasites: obligate bacterial patho-

gens, hypoviruses, facultative parasites, and predators. In hyperparasitism, the

pathogen is directly attacked by a specific BCA that kills it or its propagules.

Pasteuria penetrans is an obligate bacterial pathogen of root-knot nematodes that

has been used as a BCA. There are several fungal parasites of plant pathogens,

including those that attack sclerotia (e.g., Coniothyrium minitans) while others

attack living hyphae (e.g., Pythium oligandrum). And, a single fungal pathogen can

be attacked by multiple hyperparasites. For example, Acremonium alternatum,

Acrodontium crateriforme, Ampelomyces quisqualis, Cladosporium oxysporum,

and Gliocladium virens are just a few of the fungi that have the capacity to parasitize

powdery mildew pathogens (Kiss 2003). Other hyperparasites attack plant-

pathogenic nematodes during different stages of their life cycles (e.g., Paecilomyces

lilacinus and Dactylella oviparasitica). In contrast to hyperparasitism, microbial

predation is more general and pathogen nonspecific and generally provides less

predictable levels of disease control. Some BCAs exhibit predatory behavior under

nutrient-limited conditions. However, Trichoderma produce a range of enzymes

that are directed against cell walls of fungi (Benhamou and Chet 1997).

Table 2 Antagonism responsible for biological control of plant pathogens

Type Mechanism adopted

Direct antagonism Hyperparasitism/predation

Examples: lytic/some nonlytic mycoviruses Lysobacter

enzymogenes, Pasteuria penetrans, Trichoderma virens

Mixed-path antagonism Antibiotics

Mode: 2,4 diacetylphloroglucinol, phenazines, cyclic

lipopeptides

Lytic enzymes

Examples: chitinases, glucanases, proteases

Unregulated waste products

Examples: ammonia, carbon dioxide, hydrogen cyanide

Physical/chemical interference

Indirect antagonism Competition

Mode: exudates/leachates consumption, siderophore

scavenging, physical niche occupation

Induction of host resistance

Mode: contact with fungal cell walls, detection of pathogen-

associated molecular patterns, phytohormone-

mediated induction

Modified from Pal and Gardener (2006)

Varma_Ch14.indd 295Varma_Ch14.indd 295 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

296 S. Tripathi et al.

7.2.2 Antibiotic-mediated Suppression

Microbial toxins that kill other microorganisms at low concentrations are known as

antibiotics. Most microbes produce and secrete one or more compounds with anti-

biotic activity. In some instances, antibiotics produced by microorganisms have

been shown to be particularly effective at suppressing plant pathogens and the

diseases they cause. Some examples of antibiotics reported to be involved in plant

pathogen suppression are listed in Table 3. In all cases, the antibiotics have been

shown to be particularly effective at suppressing growth of the target pathogen in

vitro and/or in situ. Several biocontrol strains are known to produce multiple

antibiotics which can suppress one or more pathogens. The ability to produce

multiple antibiotics probably helps to suppress diverse microbial competitors,

some of which are likely to be plant pathogens. The ability to produce multiple

classes of antibiotics, that differentially inhibit different pathogens, is likely to

enhance biological control. More recently, Pseudomonas putida WCS358r strains

genetically engineered to produce phenazine and DAPG (2,4-diacetyl-phloroglucinol)

displayed improved capacities to suppress plant diseases in field-grown wheat

(Glandorf et al. 2001).

7.2.3 Lytic Enzymes and Other Byproducts of Microbial Life

Many microorganisms produce and release lytic enzymes that can hydrolyze a wide

variety of polymeric compounds, including chitin, proteins, cellulose, hemicellu-

lose, and DNA. Expression and secretion of these enzymes by different microbes

can sometimes result in the suppression of plant pathogen activities directly. For

example, control of Sclerotium rolfsii by Serratia marcescens appeared to be medi-

ated by chitinase expression (Ordentlich et al. 1988). And, a b-1,3-glucanase

Table 3 Antibiotics produced by Biological Control Agents (BCA)

Organisms Antibiotics produced Target pathogen

Pseudomonas fluorescens 2,4-diacetyl-phloroglucinol Pythium sp.

Phenazines Gaeumannomyces graminis

v a r . tritici

Pyoluteorin, Pyrrolnitrin Pythium ultimum Rhizoctonia solani

Agrobacterium radiobacter Agrocin 84 Agrobacterium tumefaciens

Bacillus subtilis Bacillomycin D Aspergillus flavus

Iturin A Botrytis cinerea R. solani

Mycosubtilin Pythium aphanidermatum

Bacillus cereus Zwittermicin A Phytophthora medicaginis

P. aphanidermatum

Bacillus amyloliquefaciens Bacillomycin, Fengycin Fusarium oxysporum

Lysobacter sp. Xanthobaccin A Aphanomyces cochlioides

Trichoderma virens Gliotoxin R. solani

Modified from Pal and Gardener (2006)

Varma_Ch14.indd 296Varma_Ch14.indd 296 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 297

contributes significantly to biocontrol activities of Lysobacter enzymogenes strain

C3 (Palumbo et al. 2005). While they may stress and/or lyse cell walls of living

organisms, these enzymes generally act to decompose plant residues and nonliving

organic matter. Microbes showing a preference for colonizing and lysing plant

pathogens are classified as biocontrol agents. Lysobacter and Myxobacteria are

known to produce lytic enzymes, and some isolates have been shown to be effective

at suppressing fungal plant pathogens.

7.2.4 Competition

From a microbial perspective, soils and living plant surfaces are frequently nutrient-

limited environments. To successfully colonize the phytosphere, a microbe must

effectively compete for the available nutrients. On plant surfaces, host-supplied

nutrients include exudates, leachates, or senesced tissue. In general, soilborne patho-

gens, such as species of Fusarium and Pythium that infect through mycelial contact,

are more susceptible to competition from other soil- and plant-associated microbes

than those pathogens that germinate directly on plant surfaces and infect through

appressoria and infection pegs. The most abundant nonpathogenic plant-associated

microbes are generally thought to protect the plant by rapid colonization and thereby

exhausting the limited available substrates so that none are available for pathogens

to grow. At the same time, these microbes produce metabolites that suppress patho-

gens. These microbes colonize the sites where water and carbon-containing nutrients

are most readily available, such as exit points of secondary roots, damaged epidermal

cells, and nectarines, and utilize the root mucilage.

7.2.5 Induction of Host Resistance

There are numerous environmental stimuli, including gravity, light, temperature,

physical stress, water and nutrient availability, to which plants actively respond.

Plants also respond to a variety of chemical stimuli produced by soil- and plant-

associated microbes which either induce or condition plant host defenses through

biochemical changes that enhance resistance against subsequent infection by a variety

of pathogens. Recently, characterization of the determinants and pathways of induced

resistance stimulated by biological control agents and other nonpathogenic microbes

have been studied as stated in Table 4. The first of these pathways, termed systemic

acquired resistance (SAR), is mediated by salicylic acid (SA), a compound which is

frequently produced following pathogen infection, and typically leads to the expres-

sion of pathogenesis-related (PR) proteins. These PR proteins include a variety of

enzymes some of which may act directly to lyse the invading cells, reinforce cell wall

boundaries to resist infections, or induce localized cell death. A second phenotype,

first referred to as induced systemic resistance (ISR), is mediated by jasmonic acid

(JA) and/or ethylene, which are produced following applications of some nonpatho-

genic rhizobacteria. Interestingly, the SA- and JA- dependent defense pathways can

Varma_Ch14.indd 297Varma_Ch14.indd 297 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

298 S. Tripathi et al.

be mutually antagonistic, and some bacterial pathogens take advantage of this to

overcome the SAR. For example, pathogenic strains of Pseudomonas syringae

produce coronatine, which is similar to JA, to overcome the SA-mediated pathway

(He et al. 2004). Because the various host-resistance pathways can be activated to

varying degrees by different microbes and insect feeding, it is plausible that multiple

stimuli are constantly being received and processed by the plant. Thus, the magnitude

and duration of host defense induction will likely vary over time. Only if induction

can be controlled, i.e., by overwhelming or synergistically interacting with endogenous

signals, will host resistance be increased.

A number of strains of root-colonizing microbes have been identified as poten-

tial elicitors of plant host defenses. Some biocontrol strains of Pseudomonas sp. and

Trichoderma sp. are known to strongly induce plant host defenses (Haas et al. 1991;

Harman et al. 2004). In several instances, inoculations with plant-growth-promoting

rhizobacteria (PGPR) were effective in controlling multiple diseases caused by

different pathogens, including anthracnose (Colletotrichum lagenarium), angular

leaf spot (Pseudomonas syringae pv. lachrymans and bacterial wilt (Erwinia

tracheiphila). A number of chemical elicitors of SAR and ISR may be produced by

the PGPR strains upon inoculation, including salicylic acid, siderophore, lipopoly-

saccharides, and 2,3-butanediol, and other volatile substances (Van Loon et al.

1998; Ongena et al. 2004; Varma and Chincholkar 2007). Again, there may be

multiple functions to such molecules blurring the lines between direct and indirect

antagonisms. More generally, a substantial number of microbial products have been

identified as elicitors of host defenses, indicating that host defenses are likely stim-

ulated continually over the course of a plant’s lifecycle. Excluding the components

[Au4][Au4]

Table 4 Bacterial determinants and types of host resistance induced by biocontrol agents

Strains Hosts Bacterial determinants Type

Bacillus mycoides Beta vulgaris Peroxidase, chitinase and ISR

β-1,3-glucanase

Bacillus subtilis Arabidopsis 2,3-butanediol ISR

Pseudomonas fluorescens Nicotiana tabacum Siderophore SAR

Arabidopsis Antibiotics (DAPG) ISR

Raphanus sativus Lipopolysaccharide ISR

Siderophore

Iron-regulated factor

Dianthus caryophyllus Lipopolysaccharide ISR

Raphanus sativus Lipopolysaccharide ISR

Iron regulated factor

Arabidopsis Lipopolysaccharide ISR

Solanum lycopersicum Lipopolysaccharide ISR

Pseudomonas putida Arabidopsis Lipopolysaccharide ISR

Siderophore ISR

Bean Z,3-hexenal ISR

Serratia marcescens Cucumis sativus Siderophore ISR

Modified from Pal and Gardener (2006)

Varma_Ch14.indd 298Varma_Ch14.indd 298 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 299

directly related to pathogenesis, these inducers include: lipopolysaccharides and

flagellin from Gram-negative bacteri; cold shock proteins of diverse bacteria; trans-

glutaminase, elicitins, and β-glucans in Oomycetes; invertase in yeast; chitin and

ergosterol in all fungi; and xylanase in Trichoderma (Numberger et al. 2004). These

data suggest that plants would detect the composition of their plant-associated

microbial communities and respond to changes in the abundance, types, and locali-

zation of many different signals. The importance of such interactions is indicated

by the fact that further induction of host resistance pathways, by chemical and

microbiological inducers, is not always effective at improving plant health or

productivity in the field.

8 Biocontrol Research, Development and Adoption

Much has been learned from the biological control research conducted over the past

40 years. But, in addition to learning the lessons of the past, biocontrol researchers

need to look forward to define new and different questions, the answers to which

will help facilitate new biocontrol technologies and applications. Currently, funda-

mental advances in computing, molecular biology, analytical chemistry, and statis-

tics have led to new research aimed at characterizing the structure and functions of

biocontrol agents, pathogens, and host plants at the molecular, cellular, organismal,

and ecological levels.

Growers are interested in reducing dependence on chemical inputs, so biological

controls (defined in the narrow sense) can be expected to play an important role in

Integrated Pest Management (IPM) systems. To deploy biorational controls of insect

pests and diseases these include BCAs, introduced as inoculants or amendments, as

well as active ingredients directly derived from natural origins and having a low

impact on the environment and nontarget organisms, is the basic theme behind it.

9 Conclusions

In general, though, regulatory and cultural concerns about the health and safety of

specific classes of pesticides are the primary economic drivers promoting the adop-

tion of biological control strategies in urban and rural landscapes. Self-perpetuating

biological controls (e.g., hypovirulence of the chestnut blight pathogen) are also

needed for control of diseases in forested and rangeland ecosystems where high

application rates over larger land areas are not economically-feasible. In terms of

efficacy and reliability, the greatest successes in biological control have been

achieved in situations where environmental conditions are most controlled or pre-

dictable and where biocontrol agents can preemptively colonize the infection court.

Monocyclic, soil borne and post-harvest diseases have been controlled effectively

by biological control agents that act as bioprotectants (i.e., preventing infections).

Varma_Ch14.indd 299Varma_Ch14.indd 299 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

300 S. Tripathi et al.

Specific applications for high value crops targeting specific diseases (e.g., fire-

blight, downy mildew, and several nematode diseases) have also been adopted.

There is considerable interest in the exploitation of microbial biological control

agents (MBCAs) for the control of crop pests, weeds and diseases. MBCAs can be

used where chemical pesticides are banned or being phased out or where pests have

developed resistance to standard chemicals. The use of MBCAs can play an impor-

tant role in crop protection, as a key element in integrated pest management (IPM)

programmes. However, despite considerable research efforts on the development of

new biological control agents, the number of such products on the market is still

extremely low. In areas that previously constrained the commercialization of

MBCAs, discovery, fermentation, formulation and application, significant progress

has been made. Initiatives by stakeholders from industry, science, regulatory

authorities, policy and environment are underway to accelerate market introduction

of MBCAs. As research unravels the various conditions needed for successful bio-

control of different diseases, the adoption of MBCAs in IPM systems is bound to

increase in the years ahead.

Acknowledgments Authors Swati Tripathi, Shwet Kamal and Ajit Varma are thankful to Dr.

Ashok k Chauhan, Founder President, Amity University Noida Uttar Pradesh for encouragement.

Partial financial support received from CSIR, New Delhi is duly acknowledged. Our special

thanks are due to Prof. Dr. Karl-Heinz Kogel, Giessen, Germany for providing the original photo-

graphs on Impact of P. indica on salt-stress tolerance and root infections by F. culmorum in Barley

(Figs. 4a and b).

References

Alabouvette C, Schippers B, Lemanceau P, Bakker PAHM (1997) Biological control of Fusarium-

wilts: towards development of commercial product. In: Boland G J, Kuykendall L D (eds)

Plant microbe interactions and biological control. Dekker, New York, pp 15–36

Avio L, Pellegrino E, Bonari E, Giovannetti M (2006) Functional diversity of arbuscular mycor-

rhizal fungal isolates in relation to extraradical mycelial networks. New Phytol 172:347–357

Azcón-Aguilar C, Barea JM (1992) Interactions between mycorrhizal fungi and other rhizosphere

microorganisms. In: Allen MJ (eds) Mycorrhizal functioning. An integrative plant-fungal

process. Routledge, Chapman & Hall, New York, pp 163–198

Azcón-Aguilar C, Barea JM (1996) Arbuscular mycorrhizas and biological control of soil-borne

plant pathogens. An overview of the mechanisms involved. Mycorrhiza 6:457–464

Bacon CW (1993) Abiotic stress tolerances (moisture and nutrients) and photosynthesis in endo-

phyte-infected tall fescue. Agric Ecosyst Environ 44:123–141

Baldock JA, Masiello CA, Gélinas Y, Hedges J I (2004) Cycling and composition of organic mat-

ter in terrestrial and marine ecosystems. Mar Chem 92:39–64

Barea J M (1997) Mycorrhiza/bacteria interactions on plant growth promotion. In:Ogoshi A,

Kobayashi L, Homma Y, Kodama F, Kondon N, Akino S (eds) Plant growth-promoting rhizo-

bacteria, present status and future prospects. OECD, Paris, pp 150–158

Bashan Y (1999) Interactions of Azospirillum spp. in soils: a review. Biol Fertil Soils 29:246–256

Bashan Y, Gonzalez LE (1999) Long-term survival of the plant-growth-promoting bacteria

Azospirillum brasilense and Pseudomonas fluorescens in dry alginate inoculant. Appl

Microbiol Biotechnol 51:262–266

Varma_Ch14.indd 300Varma_Ch14.indd 300 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 301

Bedini S, Avio L, Argese E, Giovannetti M (2007) Effects of long-term land use on arbuscular

mycorrhizal fungi and glomalin-related soil protein. Agric Ecosys Environ 120:463–466

Benhamou N, Chet I (1997) Cellular and molecular mechanisms involved in the intersection between

Trichoderma harzianum and Pythium ultimum. Appl Environ Microbiol 63:2095–2099

Bertrand H, Nalin R, Bally R, Cleyet-Marel JC (2001) Isolation and identification of the most

efficient plant growth-promoting bacteria associated with canola (Brassica napus). Biol Fert

Soils 33:152–156

Bestel-Corre G, Dumas-Gaudot E, and Gianinazzi S (2004) Proteomics as a tool to monitor plant-

microbe endosymbioses in the rhizosphere. Mycorrhiza 14:1–10

Biermann B, Linderman RG (1983) Use of vesicular-arbuscular mycorrhizal roots, intraradical

vesicles and extraradical vesicles as inoculum. New Phytol 95:97–105

Bills GF, Polishook JD (1992) Recovery of endophytic fungi from Chamaecyparis thyroides.

Sydowia 44:1–12

Biological Control of Plant Diseases (2007) Eds. S. Chincholkar and K.G Mukerji. The Haworth

Press

Boddy L, Griffith GS (1989) Role of endophytes and latent invasion in the development of decay

communities in sapwood of angiospermous trees. Sydowia 41:41–73

Broek AV, Vanderleyden J (1995) Genetics of the Azospirillum-plant root association. Crit Rev

Plant Sci 14:445–466

Brunner F, Petrini O (1992) Taxonomic studies of Xylaria species and xylariaceous endophytes by

isozyme electrophoresis. Mycol Res 96:723–733

Budi SW, van Tuinen D, Martinotti G, Gianinazzi S (1999) Isolation from the Sorghum bicolor

mycorrhizosphere of a bacterium compatible with arbuscular mycorrhiza development and

antagonistic towards soilborne fungal pathogens. Appl Environ Microbiol 65:5148–5150

Bultman TL, Murphy JC (2000) Do fungal endophytes mediate wound-induced resistance? In:

Bacon CW, White JF (eds) Microbial endophytes. Dekker, New York, pp 421–452

Carroll G (1988) Fungal endophytes in stems and leaves: from latent pathogen to mutualistic

symbiont. Ecology 69:2–9

Catska V (1994) Interrelationship between vesicular-arbuscular mycorrhiza and rhizosphere

microflora in apple replant disease. Biol Plant 36:99–104

Cheplick GP, Clay K (1988) Acquired chemical defenses in grasses: the role of fungal endophytes.

Oikos 52:309–318

Chin-A-Woeng TFC, Thomas-Oates JE, Lugtenberg BJJ, Bloemberg GV (2001). Introduction

of the phzH gene of Pseudomonas chlororaphis PCL1391extends the range of biocontrol

ability of phenazine1carboxylic acid producing Pseudomonas. Mol Plant Microb Interact

14:1006–1015

Clay K (1987) Effect of fungal endophytes on the seed and seedling biology of Lolium perenne

and Festuca arundinaceae. Oecologia 73:358–362

Clay K (1990) Fungal endophytes of grasses. Annu Rev Ecol Syst 21:275–297

Clay K (1991) Fungal endophytes, grasses and herbivores. In: Barbosa P, Krischik VA, Jones CG

(eds) Microbial mediation of plant herbivore interactions. Wiley, New York, pp 199–226

Compant S, Duffy B, Nowak J, Clément C, Barka E A (2005) Use of plant growth-promoting

bacteria for biocontrol of plant diseases: principles, mechanisms of action, and future pros-

pects. Appl Environ Microbiol 71:4951–4959

Dahlman DL, Eichenseer H, Siegel MR (1991) Chemical perspective on endophyte grass interac-

tions and their implications to insect herbivory. In: Barbosa P, Krischik VA, Jones CG (eds)

Microbial mediation of plant herbivore interactions. Wiley, New York, pp 227–252

Daniell TJ, Husband R, Fitter AH, Young JPW (2001) Molecular diversity of arbuscular mycor-

rhizal fungi colonising arable crops. FEMS Microbiol Ecol 36:203–209

Defago G, Keel C (1995) Pseudomonads as biocontrol agents of diseases caused by soilborne

pathogens In: Hokkanen HMT, Lynch JM (eds) Benefits and risks of introducing biocontrol

agents. Cambridge University Press, Cambridge

[Au5][Au5]

Varma_Ch14.indd 301Varma_Ch14.indd 301 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

302 S. Tripathi et al.

Diedhiou PM, Hallmann J, Oerke EC, Dehne HW (2003) Effects of arbuscular mycorrhizal fungi

and a non-pathogenic Fusarium oxysporum on Meloidogyne incognita infestation of tomato.

Mycorrhiza 13:199–204

Dobbelaere S, Croonenborghs A, Thys A, Vande Browk A, Vanderleyden J (1999) Phytostimulatory

effect Azospirillum brasilense strains and auxins on wheat. Plant Soil 212:155–164

Dobbelaere S, Croonenborghs A, Thys A, Ptacek D, Vanderleyden J, Dutto P, Labandera-Gonzalez

C, Caballero-Mellado J, Aguirre JF, Kapulnik Y, Brener S, Burdman S, Kadouri D, Sarig S,

Okon Y (2001) Response of agronomically important crops to inoculation with Azospirillum.

Aust J Plant Physiol 28:1–9

Duchesne LC (1994) Role of ectomycorrhizal fungi in biocontrol. In: Pfleger FL, Linderman RG

(eds) Mycorrhizae and plant health. APS Press, St. Paul, Minn., pp 27–45

Duijff BJ, Pouhair D, Olivain C, Alabouvette C, Lemanceau P (1998) Implication of systemic

induced resistance in the suppression of Fusarium wilt of tomato by Pseudomonas fluorescens

WCS417r and nonpathogenic Fusarium oxysporum Fo47. Eur J Plant Pathol 104:903–910

Dumas-Gaudot E, Gollotte A, Cordier C, Gianinazzi S, Gianinazzi-Pearson V (2000) Modulation

of host defence systems In: Kapulnick Y, Douds Jr DD (eds) Arbuscular mycorrhizas: physiol-

ogy and functions. Kluwer, Dordrecht, pp 121–140

El Zemrany H, Cortet J, Lutz MP, Chabert A, Baudoin E, Haurat J, Maughan N, Félix D, Défago G,

Bally R, Moënne-Loccoz Y (2006) Field survival of the phytostimulator Azospirillum lipoferum

CRT1 and functional impact on maize crop, biodegradation of crop residues, and soil faunal

indicators in a context of decreasing nitrogen fertilization. Soil Biol Biochem 38:1712–1726

Farmer E E (2007) Plant biology: jasmonate perception machines. Nature 448:659–660

Fisher PJ, Anson AE, Pertini O (1984a) Antibiotic activity of some endophytic fungi from erica-

ceous plants. Bot Helvet 94:249–253

Fisher PJ, Anson AE, Pertini O (1984b) Novel antibiotic activity of an endophyte Cryptosporiopsis

sp. isolated from Vaccinium myrtillus. Trans Br Mycol Soc 83:145–148

Fitter AH, Garbaye J (1994) Interactions between mycorrhizal fungi and other soil organisms.

Plant Soil 159:123–132

Franken P, Requena N (2001) Analysis of gene expression in arbuscular mycorrhizas: new

approaches and challenges. New Phytol 150:517–523

Gange AC, Whitfield L, Ixer-Pitfield S (2004) Assessment of arbuscular mycorrhizal fungi as

potential biocontrol agents for Poa annua L. in fine turf. J Turfgrass Sports Surface Sci 80

Garbeva P, van Veen JA, van Elsas J D (2004) Microbial diversity in soil: selection of microbial

populations by plant and soil type and implications for disease suppressiveness. Annu Rev

Phytopathol 42:243–270

Garcia-Garrido JM, Ocampo JA (1989) Effect of VA mycorrhizal infection of tomato on damage

caused by Pseudomonas syringae. Soil Biol Biochem 21:165–167

Garcia-Garrido JM, Tribak M, Rejon-Palomares A, Ocampo JA, Garcia-Romera I (2000)

Hydrolytic enzymes and ability of arbuscular mycorrhizal fungi to colonize roots. J Exper Bot

51:1443–1448

Garmendia I, Goicoechea N, Aguirreolea J (2005) Moderate drought influences the effect of

arbuscular mycorrhizal fungi as biocontrol agents against Verticillium-induced wilt in pepper.

Mycorrhiza 15:345–356

Gasoni L, Stegman De Gurfinkel B (1997) The endophyte Cladorrhinum foecundissimum in cot-

ton roots: phosphorus uptake and host growth. Mycol Res 101:867–870

Gianinazzi-Pearson V, Dumas-Gaudot E, Gollotte A, Tahiri-Alaoui A, Gianinazzi S (1996)

Cellular and molecular defence-related root responses to invasion by arbuscular mycorrhizal

fungi. New Phytol 133:45–57

Giovannetti M (2000) Spore germination and pre-symbiotic mycelial growth In: Kapulnick Y,

Douds Jr. DD (eds) Arbuscular mycorrhizas: physiology and functions. Kluwer, Dordrecht, pp

47–68

Giri B, Giang P H, Kumari R, Prasad R, Sachdev M, Garg A P, Oelmuller R and Varma A (2004)

Mycorrhizosphere: strategies and functions. In: Buscot F, Varma A (eds) Micro-organisms in

soils: roles in genesis and functions. Soil biology series. Springer, Heidelberg, pp 213–252

Varma_Ch14.indd 302Varma_Ch14.indd 302 4/23/2008 7:26:30 AM4/23/2008 7:26:30 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 303

Glandorf DC, Verheggen P, Jansen T, Jorritsma JW, Smit E, Leefang P, Wernars K, Thomashow

LS, Laureijs E, Thomas-Oates JE, Bakker PA, Van Loon LC (2001) Effect of genetically modi-

fied Pseudomonas putida WCS358r on the fungal rhizosphere microflora of field-grown

wheat. Appl Environ Microbiol 67:3371–3378

Glick BR (1995) The enhancement of plant growth by free-living bacteria. Can. J. Microbiol

41:109–117

Guenoune D, Galili S, Phillips DA, Volpin H, ChetOkon Y, Kapulnik Y (2001) The defense

response elicited by the pathogen Rhizoctonia solani is suppressed by colonization of the AM-

fungus Glomus intraradices. Plant Sci. 160:925–932

Haas D, Keel C, Laville J, Maurhofer M, Oberliansli T, Schnider U, Voisard C, Wüthrich B,

Defago G (1991) Secondary metabolites of Pseudomonas fluorescens strain CHA0 involved in

the suppresion of root diseases. In: Hennecke H, Verma DPS (eds) Advances in molecular

genetics of plant-microbe interactions. Kluwer, Dordrecht, pp 450–456

Hameeda B, Harini G, Rupela OP, Reddy G. (2007) Effect of composts or vermicomposts on sor-

ghum growth and mycorrhizal colonization. Afr J Biotechnol 6:009–012

Harman GE, Howell CR, Vitarbo A, Chet I, Lorito M (2004) Trichoderma species- opportunistic,

avirulent plant symbionts. Nat Rev Microbiol 2:43–56

Harrier LA, Watson CA (2004) The potential role of arbuscular mycorrhizal (AM) fungi in the

bioprotection of plants against soil-borne pathogens in organic and/or other sustainable farm-

ing systems. Pest Manage Sci 60:149–157

He P, Chintamanani S, Chen Z, Zhu L, Kunkel BN, Alfano JR, Tang X, Zhou JM (2004)

Activation of a COI1-dependent pathway in Arabidopsis by Pseudomonas syringae type III

effectors and coronatine. Plant J 37:589–602

Hoitink HAJ, Boehm MJ (1999) Biocontrol within the context of soil microbial communities: a

substrate dependent phenomenon. Annu Rev Phytopathol 37:427–446

Iavicoli A, Boutet E, Buchala A, Métraux J P (2003) Induced systemic resistance in Arabidopsis

thaliana in response to root inoculation with Pseudomonas fluorescens CHA0. Mol Plant

Microb Interact 16:851–858

James HG (2001) What Do Root Pathogens See in Mycorrhizas? New Phytol 149:357–359

Jordaan A, Taylor J E, Rossenkhan R (2006) Occurrence and possible role of endophytic fungi

associated with seed pods of Colophospermum mopane (Fabaceae)in Botswana. (Published

online) http://www.sciencedirect.com/science/journal/02546299

Kimmons CA (1990) Nematode reproduction on endophyte infected and endophyte free tall fes-

cue. Plant Dis 74:757–761

Kiss L (2003) A review of fungal antagonists of powdery mildews and their potential as biocontrol

agents. Pest Manage Sci 59:475–483

Kloepper JW (1994) Plant growth-promoting rhizobacteria (other systems) In: Okon Y (ed)

Azospirillum/plant associations. CRC Press, Boca Raton, pp 111–118

Kulik MM (1988). Observations by scanning electron and brightfield microscopy on the mode of

penetration of soybean seedlings by Phomopsis phaseoli. Plant Dis 72:115–118

Kuster H, Becker A, Firnhaber C, Hohnjec N, Manthey K, Perlick A M, Bekel T, Dondrup M,

Henckel K, Goesmann A, Meyer F, Wipf D, Requena N, Hildebrandt U, Hampp R, Nehls U,

Krajinski F, Franken P, Puhler A (2007) Development of bioinformatic tools to support

EST-sequencing, in silico- and microarray-based transcriptome profiling in mycorrhizal

symbioses. Phytochemistry 38:19–32

Lacey LA, Frutos R, Kaya HK,Vail P (2001) Insect pathogens as biological control agents: do they

have a future? Biol Control 21:230–248

Lambrecht M, Okon Y, Vande Broek A, Vanderleyden J (2000) Indole-3-acetic acid, a reciprocal

signalling molecule in bacteria-plant interactions. Trends Microbiol 8:298–300

Latch GCM, Hunt WF, Musgrave DR (1985) Endophytic fungi affect growth of perennial rye

grass. NZ J Agric Res 28:165–168

Lemanceau P, Alabouvette C (1993). Suppression of Fusarium-wilts by fluorescent pseudomon-

ads: mechanisms and applications. Biocontrol Sci Technol 3:219–234

Lewis DH (1973) Concept in fungal nutrition and the origin of biotrophy. Biol Rev 48:261–278

[Au6][Au6]

Varma_Ch14.indd 303Varma_Ch14.indd 303 4/23/2008 7:26:31 AM4/23/2008 7:26:31 AM

Uncorrected Proof

304 S. Tripathi et al.

Li HY, Yang GD, Shu HR, Yang YT, Ye BX, Nishida I, Zheng CC (2006) Colonization by the

arbuscular mycorrhizal fungus Glomus versiforme induces a defense response against the root-

knot nematode Meloidogyne incognita in the grapevine (Vitis amurensis Rupr.), which

includes transcriptional activation of the class III chitinase gene VCH3. Plant Cell Physiol

47:154–63

Linderman RG (1994) Role of VAM fungi in biocontrol. In: Pfleger FL, Linderman RG (eds)

Mycorrhizae and plant health. APS Press, St Paul, pp 1–26

Linderman RG (2000) Effects of mycorrhizas on plant tolerance to diseases.In: Kapulnik Y,

Douds DD Jr. (eds) Arbuscular mycorrhizas: physiology and function. Kluwer, Dordrecht,

pp 345–365

Marschner P, Rengel Z (2007) Nutrient Cycling in Terrestrial Ecosystems. Springer Verlag Germany

McKellar ME, Nelson EB (2003) Compost-induced suppression of Pythium damping-off is medi-

ated by fatty-acid-metabolizing seed-colonizing microbial communities. Appl Environ

Microbiol 69:452–460

Miller JD (1986). Toxic metabolites of epiphytic and endophytic fungi of conifers needles. In:

Fokkema NJ, Heuvel JVD (eds) Microbiology of phyllosphere. Cambridge University Press,

Cambridge, pp 223–231

Miller RM, Jastrow JD (2000) Mycorrhizal fungi influence soil structure. In: Kapulnik Y, Douds

DD Jr. (eds) Arbuscular mycorrhizas: physiology and functions. Kluwer, Dordrecht, pp 3–18

Morris PF, Ward EWR (1992) Chemoattraction of zoospores of the plant soybean pathogen,

Phytophthora sojae, by isoflavones. Physiol Mol Plant Pathol 40:17–22

Morton JB, Benny GL (1990) Revised classification of arbuscular mycorrhizal fungi (zygomyc-

etes): a new order glomales, two new suborders, glomineae and gigasporineae and gigaspora-

ceae, with an amendation of glomaceae. Mycotaxon 37:471–491

Morton JB, Redecker D (2001) Two new families of Glomales, Archaeosporaceae and Paraglomaceae,

with two new genera Archaeospora and Paraglomus, based on concordant molecular and

morphological characters. Mycologia 93:181–195

Muirhead IF, Deverall BJ (1981) Role of appressoria in latent infection of banana fruits by

Colletotrichum musae. Physiol Plant Pathol 19:77–84

Mukerji KG, Ciancio A (2007) Mycorrhizae in the integrated pest and disease management. In:

Ciancio A, Mukerji KG (eds) General concepts in integrated pest and disease management,

Springer, Heidelberg, pp 245–266

Mukerji KG, Mandeep and Varma A (1998) Mycorrhizosphere microrganisms: screening and

evaluation. In: Varma A (ed) Mycorrhiza manual. Springer, Heideberg, pp 85–98

Numberger T, Brunner F, Kemmerling B and Piater L (2004) Innate immunity in plants and ani-

mals:striking similarities and obvious differences. Immunol Rev 198:249–266

O’Donnell J, Dickinson CH (1980) Pathogenicity of Alternaria and Cladosporium isolated on

Phaseolus. Trans Br Mycol Soc 74:335–342

Ocón A, Hampp R and Requena N (2007) Trehalose turnover during abiotic stress in arbuscular

mycorrhizal fungi. New Phytol 174:879–891

Odum EP (1953) Fundamentals of ecology. Saunders, Philadelphia

Ongena M, Duby F, Rossignol F, Fouconnier ML, Dommes J and Thonart P (2004) Stimulation

of the lipoxygenase pathway is associated with systemic resistance induced in bean by a

nonpathogenic Pseudomonas strain. Mol. Plant Microb Interact 17:1009–1018

Ordentlich A, Elad Y, Chet I (1988) The role of chitinase of Serratia marcescens in the biocontrol

of Sclerotium rolfsii. Phytopathology 78:84–88

Pal KK, B McSpadden Gardener (2006) Biological control of plant pathogens. The plant health

instructor DOI: 10.1094/PHI-A-2006–1117–02

Palumbo JD, Yuen GY, Jochum CC, Tatum K, and Kobayashi DY (2005) Mutagenesis of beta-1,3-

glucanase genes in Lysobacter enzymogenes strain C3 results in reduced biological control

activity toward Bipolaris leaf spot of tall fescue and Pythium damping-off of sugar beet.

Phytopathology 95:701–707

Pawlowska TE, Taylor JW (2004) Organization of genetic variation in individuals of arbuscular

mycorrhizal fungi. Nature 427:733–737

[Au7][Au7]

Varma_Ch14.indd 304Varma_Ch14.indd 304 4/23/2008 7:26:31 AM4/23/2008 7:26:31 AM

Uncorrected Proof

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents 305

Peters S, Aust AJ, Draeger S, Schulz B (1998) Interaction in dual cultures of endophytic fungi

with host and non-host plant calli.. Mycologia 90:360–367

Petrini O (1991) Fungal. endophytes of tree leaves. In: Andrews J, Hirano S (eds) Microbila ecol-

ogy of leaves. Springer, Heidelberg, pp 179–197

Petrini O (1996) Ecological and physiological aspect of host specificity in endophytic fungi. In:

Redlin SC, Carris LM (eds) Endophytic fungi in grasses and woody plants. APS Press, St Paul,

Minn

Petrini O, Fisher PJ, Petrini LE (1992) Fungal endophytes of bracken (Pteridium aquilinum) with

some reflections on their use in biological control. Sydowia 44:282–293

Probanza A, Lucas García JA, Ruiz Palomino M, Ramos B, Gutiérrez Mañero FJ (2002) Pinus

pinea L. seedling growth and bacterial rhizosphere structure after inoculation with PGPR

Bacillus (B. licheniformis CECT 5106 and B. pumillus CECT 5105). Appl Soil Ecol

20:75–84

Rabie GH, Almadini AM (2005) Role of bioinoculants in development of salt-tolerance of Vicia

faba plants under salinity stress. Afr J Biotechnol 4 :210–222

Ramarathnam R, Dilantha FWG (2006) Preliminary phenotypic and molecular screening for

potential bacterial biocontrol agents of Leptosphaeria maculans, the blackleg pathogen of

canola. Biocontrol Sci Technol 16:567–582

Redecker D, Morton JB, Bruns TD (2000) Ancestral lineages of arbuscular mycorrhizal fungi

(Glomales). Mol Phylogenet Evol 14:276–284

Requena N, Perez-Solis E, Azcón-Aguilar C, Jeffries P, Barea JM (2001) Management of indige-

nous plant-microbe symbioses aids restoration of desertified. Appl Environ Microbiol

67:495–498

Requena N, Serrano E, Ocon A, Breuninger M (2007) Plant signals and fungal perception during

arbuscular mycorrhiza establishment. Phytochemistry 68:33–40

Ross EW, Marx DM (1972) Susceptibility sand pine to Phytophthora cinnamomi. Phytopathology

62:1197–1200

Sanders IR, Clapp JP, Wiemken A (1996) The genetic diversity of arbuscular mycorrhizal fungi

in natural ecosystems - a key to understanding the ecology and functioning of the mycorrhizal

symbiosis. New Phytol 133:123–134

Scheffknecht S, Mammerler R, Steinkellner S, Vierheilig H (2006) Root exudates of mycorrhizal

tomato plants exhibit a different effect on microconidia germination of Fusarium oxysporum

f. sp. lycopersici than root exudates from non-mycorrhizal tomato plants. Mycorrhiza

16:365–70

Schulz B, Guske S, Dammann U, Boyle C (1998) Endophyte-host interactions.II. Defining sym-

biosis of the endophyte-host interaction. Symbiosis 25:213–227

Schüßler A, Schwarzott D, Walker C (2001) A new fungal phylum, the Glomeromycota: phylog-

eny and evolution. Mycol Res 105:1421–1423

Serfling A, Wirsel SGR, Lind V, Deising HB (2007) Performance of the biocontrol fungus

Piriformospora indica on wheat under greenhouse and field Conditions. Phytopathology

97:523–531

Shahollari B, Varma A, Oelmüller R (2005) Expression of a receptor kinase in roots is stimulated

by the basidiomycete Piriformospora indica and the protein accumulates in Triton-X-100

insoluble plasma membrane microdomains. J Plant Physiol 162:945–958

Sherameti I, Shahollari B, Venus Y, Altschmied L, Varma A, Oelmuller R (2005) The endophytic

fungus Piriformospora indica stimulates the expression of nitrate reductase and the starch-

degrading enzyme glucan-water dikinase in tobacco and Arabidopsis roots through a homeo-

domain transcription factor that binds to a conserved motif in their promoters. J Biol Chem

280:26241–26247

Shoresh M, Yedidia I, Chet I (2005) Involvement of jasmonic acid/ethylene signaling pathway in

the systemic resistance induced in cucumber by Trichoderma asperellum T203. Phytopathology

95:76–84

Siddiqui Z, Akhtar M (2006) Biological control of root-rot disease complex of chickpea by AM

fungi. Arch Phytopathol Plant Prot 39:389–395

[Au8][Au8]

Varma_Ch14.indd 305Varma_Ch14.indd 305 4/23/2008 7:26:31 AM4/23/2008 7:26:31 AM

Uncorrected Proof

306 S. Tripathi et al.

Smith SE, Read DJ (1997) Mycorrhizal symbiosis. Academic, London

Stone JK (1988) Fine structure of latent infection by Rhabdocline parkeri on Douglas fir, with

observation on uninfected epidermal cells. Can J Bot 66:45–54

Suske J, Acker G (1989) Identification of endophytic hyphae of Lophodermium piceae in tissues

of green, symptomless Norway spruce needles by immunoelectorn microscopy. Can J Bot

67:1768–1774

Tejesvi MV, Mahesh B, Nalini MS, Prakash HS, Kini KR, Subbiah V, Shetty HS (2006)

Fungalendophyte assemblages from ethnopharmaceutically important medicinal trees. Can J

Microbiol 52:427–35

Thygesen K, Larsen J, Bødker L (2004) Arbuscular Mycorrhizal Fungi Reduce Development of

Pea Root-rot caused by Aphanomyces euteiches using Oospores as Pathogen Inoculum. Eur J

Plant Pathol 110:411–419

Van de Broek A, Lambrecht M, Vanderleyden J (1999) Auxins upregulate expression of

the indole-3-pyruvate decaboxylase gene from Azospirillum brasilense. J Bacteriol

181:1338–1342

Van Loon LC, Bakker PAHM, Pieterse CMJ (1998) Systemic resistance induced by rhizosphere

bacteria. Annu Rev Phytopathol 36:453–483

Varma A, Chincholkar S (eds) (2007) Microbial siderophores, Springer, Heidelberg

Varma A, Verma S, Sudha, Sahay N, Bütehorn B, Franken P (1999) Piriformospora indica, a cul-

tivable plant-growth-promoting root endophyte. Appl Environ Microbiol. 65:2741–2744

Vierheilig H, Piché Y (2002) Signalling in arbuscular mycorrhiza: facts and hypotheses In: Buslig

B, Manthey J (eds) Flavonoids in cell functions. Kluwer, New York, pp 23–29

Walker C, Schüßler A (2004) Nomenclatural clarifications and new taxa in the Glomeromycota.

Mycol Res 108:981–982

Waller W, Achatz B, Baltruschat H, Fodor J, Becker K, Fischer M, Heier T, Hückelhoven R,

Neumann C, von Wettstein D, Franken P, Kogel KH (2005) The endophytic fungus

Piriformospora indica reprograms barley to salt stress tolerance, disease resistance and higher

yield. Proc Natl Acad Sci USA 102:13386–13391

Weller DM, Raaijmakers J, McSpadden Gardener B, Thomashow LM (2002). Microbial popula-

tions responsible for specific soil suppressiveness to plant pathogens. Annu Rev Phytopathol

40:309–348

Wilson D (1995) Endophyte - the evolution of term, a classification of its use and definition. Oikos

73:274–276

Ziedan EHE (2006) Manipulating endophytic bacteria for biological control to soil borne diseases

of peanut. J Appl Sci Res 2:497–502

Varma_Ch14.indd 306Varma_Ch14.indd 306 4/23/2008 7:26:31 AM4/23/2008 7:26:31 AM

Uncorrected Proof

Author Queries:

[Au1]: There is no corresponding entry in the References for this citation. Please insert the

full details in the Reference list.

[Au2]: I have changed the name to “Varma” from “Verma” to match the entry in the

References. Please check and confirm

[Au3]: There is no corresponding entry in the References for this citation. Please insert the

full details in the References.

[Au4]: I have changed this citation to Harman et al. Please confirm this is correct.

[Au5]: There is no text citation for this reference. Please insert one or delete the reference.

[Au6]: There is no text citation for this reference. Please insert one or delete the reference.

[Au7]: There is no text citation for this reference. Please insert one or delete the reference.

[Au8]: There is no text citation for this reference. Please insert one or delete the reference.

Varma_Ch14.indd 307Varma_Ch14.indd 307 4/23/2008 7:26:31 AM4/23/2008 7:26:31 AM

Endophytic Bacteria for Plant Growth Promotion

Chapter

Sep 2021

Endophytic bacteria survive in close association with their host plants. These bacteria become an integral part of the host tissue system. Almost every plant species is found to be in association with these bacteria. These are the promising agents that promote their host growth even in stressed environments, like in phytoremediation. They flourish their host’s growth either directly or indirectly. Directly by accumulating nutrients and modulating the level of phytohormones. Indirectly, by producing antibiotics, cell wall degrading enzymes, nutrient limitations, and activating resistance system of the host plant against the broad spectrum phytopathogens. Today these endophytic bacteria grab the attention of scientists, as these are the potential source of sustainable agriculture. Instead of using agrochemicals which are the main cause of soil health and environmental depletion, farmers should start using these endophytes as biocontrol agents, biofertilizers, biofungicides, in seed treatment, and in the reclamation of soil contaminated with heavy metals (phytoremediation). This application promotes sustainable agriculture and prevents the growing population of the world from future hazards in agriculture. Agriculture is the basic need for human survival so it requires the attention to be secured. In this chapter, we will go to the depth of the above-mentioned topics and more about the endophytes.

Current Status and Future Perspectives on Distribution of Fungal Endophytes and Their Utilization for Plant Growth Promotion and Management of Grapevine Diseases

Article

Full-text available

Mar 2024
CURR MICROBIOL

Grapevine is one of the economically most important fruit crops cultivated worldwide. Grape production is significantly affected by biotic constraints leading to heavy crop losses. Changing climatic conditions leading to widespread occurrence of different foliar diseases in grapevine. Chemical products are used for managing these diseases through preventive and curative application in the vineyard. High disease pressure and indiscriminate use of chemicals leading to residue in the final harvest and resistance development in phytopathogens. To mitigate these challenges, the adoption of potential biocontrol control agents is necessary. Moreover, multifaceted benefits of endophytes made them eco-friendly, and environmentally safe approach. The genetic composition, physiological conditions, and ecology of their host plant have an impact on their dispersion patterns and population diversity. Worldwide, a total of more than 164 fungal endophytes (FEs) have been characterized originating from different tissues, varieties, crop growth stages, and geographical regions of grapevine. These diverse FEs have been used extensively for management of different phytopathogens globally. The FEs produce secondary metabolites, lytic enzymes, and organic compounds which are known to possess antimicrobial and antifungal properties. The aim of this review was to understand diversity, distribution, host–pathogen-endophyte interaction, role of endophytes in disease management and for enhanced, and quality production.

Biocontrol potential of endophytic fungi originated from grapevine leaves for management of anthracnose disease caused by Colletotrichum gloeosporioides

Article

Jul 2023

Unlabelled: In the present study, 51 fungal endophytes (FEs) were isolated, purified and identified from the healthy leaf segments of ten grapevine varieties based on the spore and colony morphologies and ITS sequence information. The FEs belonged to the Ascomycota division comprising eight genera viz., Alternaria, Aspergillus, Bipolaris, Curvularia, Daldinia, Exserohilum, Fusarium and Nigrospora. The in vitro direct confrontation assay against Colletotrichum gloeosporioides revealed that six isolates viz., VR8 (70%), SB2 (83.15%), CS2 (88.42%), MN3 (88.42%), MS5 (78.94%) and MS15 (78.94%) inhibited the mycelial growth of test pathogen. The remaining 45 fungal isolates showed 20-59.9% growth inhibition of C. gloeosporioides. Indirect confrontation assay manifested that the isolates MN1 and MN4a showed 79.09% and 78.18% growth inhibition of C. gloeosporioides followed by MM4 (73.63%) and S5 (71.81%) isolates. Isolate S5 and MM4 were found to produce azulene and 1,3-Cyclopentanedione, 4,4-dimethyl as antimicrobial volatile organic compounds, respectively. The 38 FEs showed PCR amplification using internal transcribed spacer universal primers. The BLAST search revealed highest similarity with the existing sequences in the database. The phylogenetic analysis revealed the occurrence of seven distinct clusters each corresponding to single genus. Supplementary information: The online version contains supplementary material available at 10.1007/s13205-023-03675-z.

Antagonistic activities of needle-leaf fungal endophytes against Fusarium spp.

Article

Jan 2020

The use of living beneficial microbes and/ or their products to control plant pathogens can offer a safer alternative to chemical treatments. In this study, needle-leaf fungal endophytes (NLE) were isolated from symptoms-free needle-leaves of two host plants collected in Cavite and Batangas, Philippines. A total of 73 NLEs were observed from three tree samples for each of the angiosperm Casuarina equisetifolia Engl. and the gymnosperm Pinus kesiya Royle ex Gordon. These were identified as belonging to 17 morphospecies. Of these, seven NLEs, mainly isolated from C. equisetifolia, were tested for their antagonistic activities against three potential plant pathogens, Fusarium oxysporum s.l. Smith & Swingle, F. solani s.l. (Mart.) Sacc., and F. moniliforme s.l. J. Sheld. using the dual-culture method at three strategies. Our results showed NLEs inhibited F. oxysporum on contact via the preventive, eradicative, and simultaneous approaches indicating that fungal endophytes may be used as potential biocontrol agents against F. oxysporum s.l..

Symbiotic fungi as biotechnological tools: Methodological challenges and relative benefits in agriculture and forestry

Article

Jul 2022

Environmental conditions are becoming increasingly challenging in managed ecosystems, especially in agricultural fields, where environmentally friendly solutions are urgently needed. Fungal symbionts offer great opportunities to enhance crop production and ecosystem sustainability under environmental stress. Some fungi are relatively well investigated (e.g., arbuscular mycorrhiza) and regularly used in commercial products, while others, such as fungal endophytes, are not well-known in this market, yet. Here, we review I) the characteristics and benefits, II) the advantages and challenges of principal isolation, preservation, inoculation, and field applications methods, and III) the environmental stress resistance mechanisms for different beneficial fungi. Utilization of mycorrhizae is still facing many challenges, particularly in terms of acquiring pure cultures and successfully establishing their symbiosis in the field. Effects of mycorrhizal associations on the above-ground organs through molecular mechanisms are not fully understood. Although biochemical values of some endophytes are well recognized, molecular mechanisms involved in endophytic-induced stress tolerance are poorly known. Fungal endophytes present several important advantages over mycorrhizal fungi including broader host range as well as straightforward isolation and application protocols. Further studies are necessary for selecting the best strains and communities, producing inoculum on a large-scale, and understanding the potential environmental hazards.

The fungal endophyte–plant interactions: Scope in sustainable agriculture

Chapter

Full-text available

Dec 2021

The term ‘endophyte’ was proposed by De Bary (1866) for the organisms that remain present inside plant tissues without causing any disease symptoms. Several species of bacterial, fungal and viral endophytes are known to colonize plant tissues. Their presence is considered ubiquitous in the plant kingdom. However, the endophyte-plant association is complex and not fully understood. Fungi are the predominant members of the endophytic community. Being filamentous, fungal endophytes (FEs) more intensively impact plant growth and metabolism. Endophyte fungi live at least some part of their life cycle inside plant tissues. Millions of different fungal species are surviving on earth, most of which have not been identified. These fungi may be common saprophytes, animal or human pathogens, phytopathogens, endophytes or mycorrhizal. Contrary to mycorrhizal fungi, the FEs grow inside plant tissues. Most of the time, such associations are symbiotic. Most endophytes enter the plant system through foliage, roots, stems and bark and could also horizontally transmit through spores, forming a ‘constitutive’ or ‘inducible’ endopohytism. The former involves endophyte-infected plants that transfer the infection vertically via seeds. The latter includes several other fungi that colonize host tissues. The roots of more than 90% of flowering plants harbor the largest pool of FEs in the plant body.

Harnessing Fungal Endophytes for natural management: a biocontrol perspective

Article

Full-text available

Dec 2023

In the ever-evolving realm of agriculture, the convoluted interaction between plants and microorganisms have assumed paramount significance. Fungal endophytes, once perceived as mere bystanders within plant tissues, have now emerged as dynamic defenders of plant health. This comprehensive review delves into the captivating world of fungal endophytes and their multifaceted biocontrol mechanisms. Exploring their unique ability to coexist with their plant hosts, fungal endophytes have unlocked a treasure trove of biological weaponry to fend off pathogens and enhance plant resilience. From the synthesis of bioactive secondary metabolites to intricate signaling pathways these silent allies are masters of biological warfare. The world of fungal endophytes is quite fascinating as they engage in a delicate dance with the plant immune system, orchestrating a symphony of defense that challenges traditional notions of plant-pathogen interactions. The journey through the various mechanisms employed by these enigmatic endophytes to combat diseases, will lead to revelational understanding of sustainable agriculture. The review delves into cutting-edge research and promising prospects, shedding light on how fungal endophytes hold the key to biocontrol and the reduction of chemical inputs in agriculture. Their ecological significance, potential for bioprospecting and avenues for future research are also explored. This exploration of the biocontrol mechanisms of fungal endophytes promise not only to enrich our comprehension of plant-microbe relationships but also, to shape the future of sustainable and ecofriendly agricultural practices. In this intricate web of life, fungal endophytes are indeed the unsung heroes, silently guarding our crops and illuminating a path towards a greener, healthier tomorrow.

Plant Endophytes in Growth Promotion and Sustainable Management of Crop Pests

Chapter

Sep 2022

Role of Endophyte Metabolites in Plant Protection and Other Metabolic Activities

Chapter

Mar 2022

Endophytes are generally symptomless microorganisms and may be of bacterial as well as fungal origin and have been found in almost all living plant species. Symbiotic association of these microorganisms with host plant by colonizing the internal tissues play valuable role in agricultural practices resulting in the improvement of crop production. Fungal endophytes produce specific secondary metabolites that promote the growth and development of host plant. Secondary metabolites of both plant and its endophytic microorganisms are produced due to symbiotic association including phenolic, flavonoids, tannins and saponins which inhibit the growth of other plant pathogen and microorganism. This chapter highlights the role of endophytes and their symbiotic association that plays a significant role in the plant defence system and other important metabolic activities.KeywordsBioremediationMetabolitesPhytohormonesRhizosphericAntagonoistic

Plant-Fungal Association: An Ideal Contrivance for Combating Plant Stress Tolerance

Chapter

Apr 2021

Plants are affected by a plethora of stresses, both biotic and abiotic which severely affect their growth, productivity and yield. These stresses are caused by bacteria, fungi, insects, nematodes, pests, drought, salinity, heavy metals (HMs), temperature, etc. Therefore, it becomes utmost important to think of sustainable and biofriendly ways to curb this problem. Plant-fungal associations can prove to be an ideal solution to this problem. Fungi not only help plants to fight against various biotic and abiotic stresses but also boost their overall growth and development. Fungi can simultaneously enhance the tolerance mechanisms in plants and also help to keep the major metabolic processes at optimum levels. Thus, in this chapter, we will separately deal with the various biotic and abiotic stresses affecting plants and also the mechanisms involved therein.

The role of chitinase of Serratia marcescens in biocontrol of Sclerotium rolfsii

Article

Full-text available

Jan 1988
PHYTOPATHOLOGY

Pseudomonads as Biocontrol Agents of Diseases Caused by Soil-borne Pathogens

Chapter

Aug 1995

Biological control of insect pests, plant pathogens and weeds, is the only major alternative to the use of pesticides in agriculture and forestry. As with all technologies, there are benefits and risks associated with their utilization. This book is the outcome of a unique gathering of specialists to discuss and debate the benefits and risks associated with biological control. After intensive interaction it was concluded that we must place greater emphasis on the benefits, while not ignoring the potential risks. The authors address the various techniques and approaches used in biological control, including state-of-the-art reports and economic and risk analyses. The book will be of interest to researchers and postgraduate students in academia and industry in biotechnology, agriculture, forestry and environmental sciences.

Two new families of Glomales, Archaeosporaceae and Paraglomaceae, with two new genera Archaeospora and Paraglomus , based on concordant molecular and morphological characters

Article

Jan 2001

Two ancestral clades of arbuscular mycorrhizal fungal species were discovered from deeply divergent ribosomal DNA sequences. They are classified here as two new families Archaeosporaceae and Paraglomaceae. Each family is phylogenetically distant from each other and from other glomalean families, despite similarities in mycorrhizal morphology and fatty acid profiles. Shared mycorrhizal morphology is not surprising, since it is highly conserved and resolves other taxa in Glomales at both family and suborder levels. At the present time, each family consists of one genus. Archaeospora (Archaeosporaceae) includes three species forming atypical Acaulospora-like spores from sporiferous saccules. Two of these species are dimorphic, forming Glomus-like spores as well. Paraglomus (Paraglomaceae) consists of two species forming spores indistinguishable from those of Glomus species. Morphological characters once considered unique, such as the sporiferous saccule defining species of Acaulosporaceae, clearly are distributed in phylogenetically distant groups. The simple design of spores of some species in Glomus also masks considerable divergence at the molecular level. It is the combination of DNA sequences, fatty acid profiles, immunological reactions against specific monoclonal antibodies, and mycorrhizal morphology which provides the basis for recognizing Archaeospora and Paraglomus. These results reinforce the value of molecular data sets in providing a clearer understanding of phylogenetic relationships, which in turn can lead to a more robust taxonomy.

Chemical perspectives on endophyte-grass interactions and their implications to insect herbivory

Chapter

Jan 1991

Interactions in dual cultures of endophytic fungi with host and nonhost plant calli

Article

May 1998

Undifferentiated plant cells may be used in simplified systems for studying the interactions between plants and fungi. We used plant calli for investigating the interactions between three endophytic fungi (Coniothyrium palmarum, Geniculosporium sp. and Phomopsis sp.) and their host and nonhost plants (Lamium purpureum and Teucrium scorodonia), showing that growth of these endophytes was specifically enhanced by calli of the host. Substance (s) secreted by the host calli were responsible for this growth response. The endophytes also secreted metabolites into the medium. These were toxic to the plant calli, irrespective of whether it was a host or nonhost interaction. Further tests demonstrated the nonspecific herbicidal nature of these substances.

Interactions between mycorrhizal fungi and other rhizosphere microorganisms

Article

Jan 1992

Role of VAM fungi in biocontrol

Article

Jan 1994

R.G. Linderman

Role of ectomycorrhizal fungi in biocontrol

Article

Jan 1994

L.C. Duchesne

Revised classification of arbuscular mycorrhizal (zygomycetes): A new order, glomales, two new sub-orders glomineae, gigasporineae, and two new families, acaulosporaceae and gigasporaceae, with an emendation of glomaceae

Article

Jan 1990

General Concepts in Integrated Pest and Disease Management

Book

Jan 2007

The first volume of the Integrated Management of Plant Pests and Diseases book series presents general concepts on integrated pest and disease management, organized in three sections. Section one (modeling, management, environment) includes chapters on infection models, resurgence and replacement, plant disease epidemiology and effects of climate change in tropical environments. Followed by two reviews on IPM in post-harvest and carrot crops. The second section (emerging technologies) includes remote sensing and information technology, integrated by reviews on Bacillus thuringiensis and the role of mycorrhizae in IPM. In the third section (molecular aspects) the management of insect-borne viruses with transmission interference, some novel products for biological control and advances in molecular detection, are discussed.

Mycorrhizal Fungi and Other Root Endophytes as Biocontrol Agents Against Root Pathogens

Abstract

Recommended publications

Beneficial Microbial Mixtures for Efficient Biocontrol of Plant Diseases: Impediments and Success

Effects of actinobacteria on plant disease suppression and growth promotion

Chapter 35. Enhanced Resistance of Plants to Disease Using Trichoderma spp.

Biological Control of Tree and Woody Plant Diseases: Current Status and Future Prospects