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LTSEM micrographs of conidial germination and germ-tube growth of Phoma clematidina on the lower leaf surface of Clematis cv. Henryi (susceptible). Figure 1, conidium with three germ tubes; Fig. 2, tropic reaction of a germ tube to an epidermal cell junction; Fig. 3, germ tube passing over a stomatal opening; Fig. 4, anastomosis between two germ tubes; Fig. 5, extracellular matrix formed under a germ tube; Fig. 6, cushion-shaped appressorium formed at a stomatal guard cell. AP = appressorium, EM = extracellular matrix, GC = guard cell, GT = germ tube, SO = stomatal opening.
Source publication
A detailed study of conidial germination, germ-tube growth and the formation of infection structures in Phoma clematidina, the causal agent of clematis wilt, is described for two clematis varieties differing in disease resistance. On both the resistant and susceptible varieties, the fungus entered leaves and stems by direct penetration of the cutic...
Context in source publication
Context 1
... clematidina was found to enter its host through direct penetration of epidermal cells and stomatal guard cells. A cushion-shaped appressorium was the most common form of infection structure, usually appearing at the end of a germ tube (Fig. 6) or directly from the conidium (Fig. 7). Occasionally, infection structures in the form of either semicircular or thin narrow protrusions originated from the germ-tube tip (Fig. 8). When germ tubes passed over cell junctions, this did not appear to induce the formation of infection ...
Citations
... In addition, the plasmalemma and chloroplast of the host is disrupted, leading to the breakdown of cellular integrity. After that, the pathogen grows intercellularly through plant tissues and colonization is followed by necrosis (Hammond and Lewis, 1987;Van De Graaf et al., 2002;Aveskamp et al., 2008). In P. tracheiphila, following this symptomless stage in citrus, the fungus becomes necrotrophic and as the infection advances basipetally, the entire tree is infected, leading to its death (Migheli et al., 2009) is an aggregation of conidiophores that produce conidia asexually and are exclusively found in coelomycetous fungi (Liu et al., 2019). ...
Phoma is the most widely distributed and omnipresent genus of the order Pleosporales and the largest genus with some 3000 taxa described so far. Of which, approximately 110 species are pathogenic that occupy varied ecological niches. The genus Phoma is polyphyletic and isn’t really delimited with unclear species boundaries that make it a taxonomically controversial genus. Fungi belonging to Phoma commonly occur on crop plants that are economically important where they cause devastating plant diseases. Pathogenic members of Phoma sensu lato species attacks crop plants with symptoms ranging from leaf blight, root rot to even wilting of the plant. In infected crop residues and field stubbles, the pathogen produces abundant pycnidia and pseudothecia which serve as the source of primary inoculum whereas repeated crops of conidia produced inside pycnidium are the main source of secondary infection during the same growing season. After successful infection, the pathogen produces various phytotoxin that alters photosynthetic efficiency, actin cytoskeleton‐based functions and causes electrolyte leakage from cells. Controlling the diseases caused by members of Phoma sensu lato is challenging and efforts have been made to identify resistant varieties that can be used in various plant breeding programs. Studies have also been conducted to devise cultural and biological control measures as well as to evaluate the efficacy of fungicides against members of Phoma sensu lato. In this review we aim to discuss the disease epidemiology and control measures that can be practiced to protect crops from Phoma diseases.
... Histopathology studies have shown that hyphae penetrate directly into the epidermal cells and then further move toward the mesophyll tissues intercellularly. Direct penetration has also been reported in fungi like Phoma medicaginis in alfalfa leaf (Castell-Miller et al., 2007), P. clematidina on clematis (Clematis spp.) leaf surface (Van de Graaf et al. 2002) and Stagonospora nodorum in wheat leaf (Solomon et al. 2006). Generally, microsclerotia form appressoria over host epidermal cells, developing hyphae which enter between epidermal cells. ...
... Histopathology studies have shown that hyphae penetrate directly into the epidermal cells and then further move toward the mesophyll tissues intercellularly. Direct penetration has also been reported in fungi like Phoma medicaginis in alfalfa leaf (Castell-Miller et al., 2007), P. clematidina on clematis (Clematis spp.) leaf surface (Van de Graaf et al. 2002) and Stagonospora nodorum in wheat leaf (Solomon et al. 2006). Generally, microsclerotia form appressoria over host epidermal cells, developing hyphae which enter between epidermal cells. ...
... Histopathology studies have shown that hyphae penetrate directly into the epidermal cells and then further move toward the mesophyll tissues intercellularly. Direct penetration has also been reported in fungi like Phoma medicaginis in alfalfa leaf (Castell-Miller et al., 2007), P. clematidina on clematis (Clematis spp.) leaf surface (Van de Graaf et al. 2002) and Stagonospora nodorum in wheat leaf (Solomon et al. 2006). Generally, microsclerotia form appressoria over host epidermal cells, developing hyphae which enter between epidermal cells. ...
... In addition to stomatal penetration by P. lingam, which has also been described by other workers (ABADIE and BOUDART, 1982;HAMMOND et al., 1985), we observed penetration of the cuticle and ingress through anticlinal epidermal cell walls. Direct penetration has been reported also for two other species of Phoma, P. macdonaldii on sunflower (ROUSTAEE et al., 2000) and P. clematidina on clematis (VAN DE GRAAF et al., 2002). ...
The study involved six test fungi previously recorded in the literature as being endophytes (Beauveria bassiana, Metarhizium anisopliae , Isaria fumosorosea, Trichoderma harzianum, Fusarium proliferatum, Chaetomium globosum), two plant pathogenic fungi (Ascochyta fabae, Plenodomus lingam) and four host plants (Vicia faba, Brassica napus, Phaseolus vulgaris, Zea mays). Aerial conidia, blastospores, or ascospores, respectively were applied to leaf surfaces by spraying or by infiltrating spore suspensions through stomata directly into the leaves. Observations using light microscopy showed that the test fungi germinated on the leaf surface but did not enter actively into the leaves. Within the leaves, germination of spores and growth of hyphae appeared to depend on the presence of damaged plant tissue. Various host reactions such as browning of epidermal cells and formation of papillae were observed. Colonization of healthy leaves by the test fungi in a manner similar to the pathogens A. fabae (on Faba bean) and P. lingam (on oilseed rape) was not observed. Spore germination and hyphal growth commenced when inoculated leaves were placed on agar medium. The results indicate that the test fungi possessed a saprotrophic rather than an endophytic life style when associated with leaf tissue of the studied hosts.
... Histopathology using quadruple stain showed that the infection hyphae penetrated directly into the epidermal cells and then further moved toward the mesophyll tissues intercellularly. Direct penetration has commonly been reported in related fungi like Phoma medicaginis in alfalfa leaf (Castell-Miller et al. 2007), P. clematidina on clematis (Clematis spp.) leaf surface (Van de Graaf et al. 2002) and S. nodorum in wheat leaf (Solomon et al. 2006). Direct penetration was mentioned by Roustaee et al. (2000) that at the point of conidia attachment of P. macdonaldii on sunflower cotyledon surface, germ tubes formed infection pegs which perforated the host cuticle through exerting mechanical pressure. ...
The infection process and life cycle of S. tanaceti in leaf lamina of pyrethrum plants was investigated using histopathology. Conidia attached firmly to the leaf surface before the infection hyphae penetrated directly into the epidermal cells of the leaf without forming appressoria. The maximum germination of conidia on leaf surface was 85 % at 54 HAI. Infection hyphae infected the epidermal and palisade parenchyma cells through the middle lamella. Brown lesions on the leaf were a result of infected necrotic epidermal cells. Extensive colonization through both intra- and intercellular hyphae along with pycnidia formation caused enormous damage to the infected cells at 12 DAI. Unlike the quadruple stain, both single and dual stains had very limited ability to visualise infection structures. These results have provided a better understanding of the physical interaction between the pathogen and the pyrethrum leaf tissues and will help to elucidate the complete disease cycle of S. tanaceti on pyrethrum plant.
... Some plant pathogenic fungi enter the trichomes, such as Colletotrichum acutatum (syn. Gloeosporium laeticolor) (Kitajima 1951(Kitajima , 1952Moriwaki et al. 2002) and Phoma clematidina (van de Graaf et al. 2002). However, as far as we know, D. theae-sinensis is the sole fungus that enters the host plant only through the trichomes (Hamaya 1982). ...
The infection process of the anthracnose fungus Disculatheae-sinensis in tea was investigated in detail by fluorescence microscopy. Leaves of the susceptible tea variety ‘Yabukita’ spray inoculated with the conidial suspension were collected sequentially and examined after fluorescence staining with fluorescein-conjugated wheat germ agglutinin. Conidia adhering to the trichomes germinated and formed very short germ tubes. Penetration hyphae grew from the germ tube tips into the cell walls of the trichomes, and formed infection hyphae by 12 h after inoculation. Hyphae that had invaded the mesophyll were confined to the small round spots that formed surrounding the infected trichomes. However, hyphae that had reached the veins extended through the phloem, causing necrosis of the neighboring mesophylls and eventually the formation of large necrotic lesions.
... Controversial is the effect of trichomes for fungal infections: While damaged trichomes are often the starting point for colonialization with powdery mildew (Erysiphe necator) on grapevine buds (Rumbolz and Gubler, 2005), Botrytis cinerea on harvested tomato (Charles et al., 2008), Phoma clematidina on clematis (Van De Graaf et al., 2002) or Beauveria bassiana on poppy (Landa et al., 2013), glandular trichomes are often able to secrete exudates with antifungal activity as shown in a wild potato species (Solanum berthaultii) and its resistance to Phytophthora infestans (Lai et al., 2000). The disease incidence correlated negatively with the density and polyphenol-oxidase activity of short type A trichomes that have a four-lobed membrane-bound gland at their tips (Lai et al., 2000). ...
Trichomes are differentiated epidermal cells on above ground organs of nearly all land plants. They play important protective roles as structural defenses upon biotic attacks such as herbivory, oviposition and fungal infections, and against abiotic stressors such as drought, heat, freezing, excess of light, and UV radiation. The pattern and density of trichomes is highly variable within natural population suggesting tradeoffs between traits positively affecting fitness such as resistance and the costs of trichome production. The spatial distribution of trichomes is regulated through a combination of endogenous developmental programs and external signals. This review summarizes the current understanding on the molecular basis of the natural variation and the role of phytohormones and environmental stimuli on trichome patterning.
... clematidina exhibits several penetration styles between direct penetration and cushion-shaped appressoria. (Van de Graaf et al. 2002) ...
Fungi belonging to the genus Phoma form a phylogenetically heterogeneous group with a broad range of possible plant hosts. Most of them do not interfere with cultivation of crops; others, especially Phoma lingam with its perfect form Leptosphaeria maculans, are the causative agent of devastating field losses in rapeseed cultivation. Efficient disease management requires profound fundamental knowledge on biology and genetics of these organisms, which needs to be transferred into practical rules, effective for disease control in the field.
Good disease management implies reliable diagnosis tools, and reasonable procedures taking into account knowledge on infection pathways, the secretion of enzymes and toxins, and on the effects that these Phoma-specific substances cause in plants. Phoma forecasting, together with reasonable fungicide and cultivation regimes, are indispensable to avoid losses. Conventional breeding programmes for resistance have already been helpful in the past. Knowledge of various avirulence genes from Leptosphaeria maculans, together with the tremendously useful information from the genome sequence, will facilitate efficient plant breeding programmes in the future.
... The infection and establishment of A. anemones in leaves of windflower was studied by light microscopy, SEM and TEM. The behavior of A. anemones on the surface of windflower showed several features, such as tropism of germ tubes in reaction to cell junctions and aspersoria formation, which are also found in many other fungal species (Graaf et al., 2002;Nicholson et al., 1991). Pathogen fungi can produce a wide array of cellular structures specialized for cell wall penetration, such as appressoria and haustoria (Mendgen and Deising, 1993). ...
Leaf spot, caused by Ascochyta anemones, is one of the major diseases of windflower in China. Histological studies of the artificially inoculated leaf tissues with A. anemones conidia were observed by light and electron microscopy to elucidate the host-pathogen interaction. Conidial germination and germ tube formation began after 4 h of inoculation. Each conidium produced one germ tube which penetrated the host surface. The fungus gain entry of the host by direct penetration of the leaf cuticle, following the formation of appressorium after 12-24 h of inoculation. Most appressoria were formed in the grooves between adjacent epidermal cells. Once the fungus was fully established, it destroyed internal tissues, resulting in diseased lesions on the leaves after 3-6 days of inoculation. Development of leaf spots and fungal pycnidia could be observed on necrotic areas within 7-14 days after inoculation.
