Content uploaded by Papori Barua
Author content
All content in this area was uploaded by Papori Barua on Mar 31, 2021
Content may be subject to copyright.
A preview of the PDF is not available
Extended survival of Puccinia graminis f. sp. tritici urediniospores: Implications for biosecurity and on-farm management
Abstract
Puccinia graminis f. sp. tritici, the causal organism of stem rust, is of global importance across wheat growing countries. However, some epidemics commence without the obvious presence of ‘alternate’ or ‘green bridge’ hosts, suggesting urediniospores can survive in the absence of suitable host plants for many weeks. Testing a range of inert material types, including metals, plastics, fabrics and woods, highlighted a significant effect of material type and temperature on urediniospore viability (P<0.001), with urediniospores remaining attached and viable on these materials (aluminium, paper, rubber, all fabric and all woods) for up to 365 days at 23°C/4°C day/night. However, at 36°C/14°C day/night, urediniospore viability was retained for a maximum of 300 days on denim and jute.. Further, at 45°C/15°C day/night, urediniospores remained viable to a maximum of 180 days on cotton and on jute. The frequency of recovery of attached urediniospores was also dependent upon the material type, with significant differences between materials in their abilities to retain urediniospores after washing (P<0.001). Urediniospores recovered even after 300 or 365 days from the lower two temperature regimes successfully initiated infections of wheat seedlings. Results confirmed the potential importance of inert materials as long-term carriers of viable stem rust of wheat (P. graminis f. sp. tritici) urediniospores, highlighting risks of spread of new pathotypes and strains across wheat growing regions, the significant biosecurity implications for contaminated carrier materials, and its likely survival across seasons without a host.
... For example, urediniospores of Puccinia graminis f. sp. tritici could survive on inert materials without a host and successfully initiate infections of wheat seedlings after 300 days, increasing the likelihood of spread of the pathogen across wheat growing regions through contaminated carrier materials (Barua et al. 2018a). Similarly, spores of Kabatiella caulivora and Leptosphaeria maculans survived on inert materials for up to 240 days (Barua et al. 2017b(Barua et al. , 2018b. ...
... There have been recent studies on survival of spores of the wheat stem rust pathogen, P. graminis f. sp. tritici (Barua et al. 2018a), the forage legume northern anthracnose pathogen, K. caulivora (Barua et al. 2017b), the rapeseed phoma stem canker pathogen, L. maculans (Barua et al. 2018b), and the rice blast pathogen, M. oryzae (Barua et al. 2017a). Subsequent in vitro studies were undertaken to determine the effect of five fungicide or disinfectant treatments [propiconazole (Tilt 2 5 0 E C ) , a z o x y s t r o b i n ( A m i s t a r 2 5 0 E C ) , didecyldimethyl ammonium chloride (Sporekill), alkali metal salts of alkylbenzene sulfonic acid and coconut diethanolamide (Farmcleanse), and potassium peroxymonosulfate (Virkon)] in preventing spore germination of these plant pathogens. ...
... Furthermore, all had been used in recent studies to define the role of different carrier materials on survival of conidia of L. maculans (Barua et al. 2018b), K. caulivora (Barua et al. 2017b) and Puccinia graminis f. sp. tritici (Barua et al. 2018a). All test materials were scrubbed under running tap water using a plastic brush for 5 min to remove any potential contaminants. ...
In vitro studies were undertaken to determine the effects of five fungicide and disinfectant treatments [propiconazole (Tilt 250EC), azoxystrobin (Amistar 250EC), didecyldimethyl ammonium chloride (Sporekill), alkali metal salts of alkylbenzene sulfonic acid and coconut diethanolamide (Farmcleanse), and potassium peroxymonosulfate (Virkon)] in preventing the germination of spores of Puccinia graminis f. sp. tritici, Kabatiella caulivora, Leptosphaeria maculans and Magnaporthe oryzae. Germination was inhibited by all fungicides and disinfectants, with maximum reductions at the manufacturer’s recommended concentration. Overall, azoxystrobin was the most effective, reducing germination of M. oryzae by 89%, L. maculans by 78% and P. graminis f. sp. tritici by 77%. Propiconazole was the most effective in reducing germination of K. caulivora by 72%. The extent of inhibition of germination was dependent on the pathogen; for example, alkali metal salts of alkylbenzene sulfonic acid and coconut diethanolamide, and potassium peroxymonosulfate were more effective on M. oryzae and P. graminis f. sp. tritici compared with L. maculans or K. caulivora. Studies undertaken to define the effectiveness of the fungicides/disinfectants reducing germination of the pathogens on five inert carrier materials (steel, fabric, wood, paper, and rubber) showed azoxystrobin and propiconazole to be the most effective, having 12–15% spore germination following decontamination treatment of carrier materials. The results demonstrate the potential for increased use of fungicides, particularly demethylation inhibitor and QoI fungicides, to decontaminate carrier materials to address the critical need to implement a practical commercial solution for dealing with threats posed by the long-term viability of these and other plant pathogens on inert materials associated with movement of humans, farming equipment, and commodities nationally and internationally.
... For example, urediniospores of Puccinia graminis f. sp. tritici could survive on inert materials without a host and successfully initiate infections of wheat seedlings after 300 days, increasingthe likelihood of spread of the pathogen across wheat growing regions through contaminated carrier materials (Barua et al. 2018a). Similarly, spores of Kabatiella caulivora and Leptosphaeria maculans survived on inert materials for up to 240 days (Barua et al. , 2018b. ...
... Furthermore, all had been used in recent studies to define the role of different carrier materials on survival of conidia of L. maculans (Barua et al. 2018b), K. caulivora () and Puccinia graminis f. sp. tritici (Barua et al. 2018a). All test materials were scrubbed under running tap water using a plastic brush for 5 min to remove any potential contaminants. ...
... Its urediniospores can survive in the absence of suitable ('alternate' or 'green bridge') host plants for many weeks. Barua et al. (2018) performed a range of tests on inert material types (metals, plastics, fabrics and woods), highlighting a significant effect of material type and temperature on urediniospore viability. Urediniospores remained attached and viable (infections initiated on wheat seedlings) on aluminium, paper, rubber, all fabric and all woods for up to 365 d at 23/8 C day/night, and on denim and jute for up to 300 d at 36/14 C day/night. ...
Megatrends are slow processes that are hardly noticeable initially, but later cause long-term global effects. The European Environmental Agency (EEA) has set 11 global megatrends. Some of them - globalization, risk of pandemic, technological development and climate change - have major impacts on microfungi in a vulnerable region of Europe, the Pannonian Biogeographical Region. Due to the globalization, high amount of inocula is imported with tropical fruits, soil and packaging materials. Due to technological development, these fungi gain new habitats in the immediate surroundings of humans. In most of the cases these are considered to be extreme environments for which fungi can increasingly adapt. As a result of climate change, non-native species are more likely to colonize the natural habitats in the region. Some of these fungal species have great effect on human health and agriculture. The effects of global megatrends on fungi raise new issues not only from the point of view of economy and health, but also from plant protection and environmental perspectives. Because of the increasing presence of these fungal species, it is important to take them into account during the development of adaptation strategies.
... Recent studies demonstrate that fungal spores can remain viable for even up to 12 months on inert materials depending upon the type of spores and the carrier material (Barua et al. 2018). Even though the spread of the pathogen is mainly through infected seed and/or infested crop debris , alternative means of entry and spread of L. maculans via attachment to different carrier materials used in daily life, farms and/or associated in the cargo and transport industry, or commonly used by travellers, also may play an important role. ...
Many plant species require prolonged cold exposure, generally encountered during the course of winter, before flowering and setting seed. Without exposure to a prolonged cold period, flowering is blocked. This process is known as vernalization. A requirement for vernalization is evolutionary adaptation to temperate climates, preventing flowering before encountering a winter season and ensuring flowering under more the favorable weather conditions of spring. The vernalization requirement is also important for the quantity and quality of crop production. In vegetative crops, early bolting and flowering caused by a low vernalization requirement can limit the potential for yield increases or devalue the products. Therefore, understanding the mechanism that regulates flowering time is important for breeding of late-bolting lines in the Brassica vegetables. In this study, we identified two FRIGIDA (FRI) genes of Brassica rapa and showed that BrFRIb functions as an activator of FLOWERING LOCUS C (FLC). There is a positive correlation between the steady state expression levels of the sum of BrFLC paralogs and days to flowering after four weeks of cold treatment, suggesting that this is an indicator of the vernalization requirement. We also showed that histone H3 lysine 27 tri-methylation (H3K27me3) accumulated after cold treatment around exon 1 of BrFLC paralogs. This H3K27me3 mark then spreads across the entire length of all BrFLC genes upon returning to warm conditions following cold exposure, indicating that BrFLCs are repressed by the accumulation of H3K27me3 and that the spreading of H3K27me3 promotes stable FLC repression. Based on these results, we consider that epigenetic modifications are involved in the vernalization requirement of B. rapa. We also identified long non-coding RNAs (lncRNAs) by RNA-sequencing in non-vernalized and vernalized plants, and compared the expression levels of lncRNAs between before and after cold treatments. We identified differentially expressed lncRNAs at the whole genome levels and three natural antisense transcripts (NATs) from BrFLC2, and two BrMAF loci, which were upregulated by shortterm cold treatments. We discuss the biological function of lncRNA in B. rapa including whether lncRNA contributes to epigenetic regulation of FLC by prolonged cold treatment.
... Recent studies demonstrate that fungal spores can remain viable for even up to 12 months on inert materials depending upon the type of spores and the carrier material (Barua et al. 2018). Even though the spread of the pathogen is mainly through infected seed and/or infested crop debris , alternative means of entry and spread of L. maculans via attachment to different carrier materials used in daily life, farms and/or associated in the cargo and transport industry, or commonly used by travellers, also may play an important role. ...
While it is increasingly well understood how plants and animals spread around the world, and how they diversify and occupy new niches, such knowledge is fairly limited for fungi and oomycetes. As is true for animals and plants, many plant pathogenic fungi have been spread anthropogenically, but, in contrast to them, only rarely as a deliberate introduction. In addition, the occupation of new niches for plant pathogenic fungi is less defined by the abiotic environment, but more by the biotic environment, as the interaction with the host plant is the major ecological determinant of fitness, especially for biotrophic and hemibiotrophic pathogens. Thus, host switches are a major driver in the diversification of pathogens, which can have an effect similar to the arrival of animals or plants on a previously uninhabited archipelago. This chapter summarises the current state of knowledge on range expansions and host jumps in plant pathogens, focusing on (hemi-)biotrophic fungi and oomycetes.KeywordsAnthropogenic spreadEvolutionHost jumps
Erysiphaceae
Oomycota
Pucciniales
Ustilaginomycotina
The viability of Moniliophthora roreri inoculum was evaluated during the micro-fermentation process of diseased and healthy pulp-seed masses and on a range of carrier materials: aluminum, cloth, glass, paper, plastic, raffia, and rubber tire. Fungal survival was assessed before the micro-fermentation (0 hours) and every 24 to 96 hours by the growth of colonies in potato-dextrose-agar and sporulation in seed shells. Colonies of M. roreri and sporulation on seed shells were observed from seeds not submitted to micro-fermentation. No growth was recovered from diseased cocoa beans after 48 hours under the micro-fermentation. The viability of M. roreri spores recovered from carrier materials was evaluated at 7, 15, 30, 45, and 100 days after inoculation (DAI) by collecting spores, plating them on Sabouraud dextrose yeast extract agar amended with chloramphenicol (50 mg L1). The viability was determined by counting germinated and ungerminated spores under a light microscope (40×) after incubating in a moist chamber at 26 ±2 °C for 72 hours. Spores maintained long-term viability on all tested carrier materials toward the end of the experiment (overall 26%), with significant differences (p < 0.05) among them. Maximum spore viability occurred at 7 and 15 DAI, with cloth and plastic carrier materials considered at high risk of acting as vehicles for the fungal spread. Mathematical models of spore viability over time were fit to the data using the Bayesian information criterion. Findings confirmed the importance of the fermentation process to hamper M. roreri growth and the potential of carrier materials for fungal dispersal.
The specific pre- and post-cold storage treatments needed to maintain the viability of urediniospores of rust fungi during storage are species dependent. Urediniospore collections are critical to assess pathogen evolution over time, but most importantly, to determine the efficacy of resistance genes in host plants. Puccinia sorghi, the causal agent of common rust of maize, can cause yield losses of up to 40% in susceptible varieties. The purpose of this study was to optimize the pre- and post-cold storage requirements of P. sorghi urediniospores. Here, we report that dried urediniospores had an 87% decrease in germination compared with undried spores. Urediniospores of P. sorghi were successfully stored at −80°C for 24 months and remained infectious, and did not require cold shock in liquid nitrogen pre-cold storage, nor a heat shock to revive them from dormancy. Urediniospores removed from storage in a freezer at −80°C germinated readily between 22°C and 55°C.
Tropical Asian grapevine leaf rust, caused by Neophysopella tropicalis, is an important grapevine disease in the tropics. The germination of N. tropicalis urediniospores in vitro is highly variable, even with standardized methodology. It has been demonstrated that at 30 °C, there is a low proportion of urediniospores germination on Petri dishes; however, at the same temperature, the severity of rust is remarkably high. The objective of this study was to estimate the proportion of urediniospores germination of N. tropicalis in vitro and in vivo at different temperatures. The in vitro assays were carried out with polystyrene dishes and the in vivo assays were performed on detached leaves of grapevines cv. Niagara Rosada and cv. Cabernet Sauvignon. A generalized beta model was fitted to the proportion of urediniospores germination as a function of temperature by non-linear regressions. The proportions of urediniospores germination of N. tropicalis were higher in vivo than in vitro, regardless the temperature. Urediniospore germination was inhibited at 35 °C. The optimal temperature for the germination of N. tropicalis urediniospores was 20 °C in vitro and 25 °C in vivo. The wide range of optimum temperature for the germination of N. tropicalis urediniospores on grapevine leaves may explain the importance of tropical Asian grapevine leaf rust in the tropics, as well as the increased disease severity observed at 30 °C.
Sustainable production and improved genetic gains can be achieved by broadening the genetic window of elite wheat germplasm. Here, we induced mutations in two spring wheat varieties, viz., NN-Gandum-1 (NN-1) and Punjab-11 (Pb-11), by exposing their seeds to ethyl methane sulfonate (EMS) and γ-rays, respectively. We characterized >3500 lines of each NN-1 and Pb-11 derived population in three consecutive generations, viz., M5, M6, and M7, for important traits, e.g., plant height, heading date, spike morphology and rust resistance. We observed significant genetic variation and correlations in both populations for all investigated traits. We observed differences in terms of number of mutants between NN-1 (22.76%) and Pb-11 (26.18%) which could be ascribed to the genotype-by-mutagen interaction. High broad-sense heritability (H2) estimates, that are vital for higher genetic gains, were observed for all of the investigated traits in both populations (H2 = 0.69–0.91 in NN-1 and 0.84–0.98 in Pb-11). Particularly, to breed for rust resistance, we selected a subset (n = 239) of M7 lines that also showed phenotypic variation for other traits. Our studies (1) show the relevance to artificial mutagenesis to create genetic variation in elite germplasm for their immediate use in current breeding programs, and (2) provide material for downstream identification of genes associated with traits of high agronomic importance.
Long-lasting viable fungal spores are one of the important aspects in emergence, spread and disease development of pathogenic fungi. We developed a rapid and miniaturized system using Alamar Blue (resazurin dye; 7-hydroxy-3H-phenoxazin-3-one 10-oxide) for assessing fungal spore viability, using the ascomycete Leptosphaeria maculans (causing blackleg disease on canola) as a ‘model pathogen’. The assay is dependent on the metabolic activity of viable fungal spores to convert the dark blue of resazurin (maximum absorbance 605 nm) into the pink colour of resorufin (maximum absorbance 573 nm). The Alamar Blue assay uses an optimised micro-titre based format that was far superior for determining fungal spore viability in comparison with current conventional techniques including trypan blue staining, a TC10 cellometer cell counter, or by assessing germination of the spores under the microscope. This new assay was also more rapid and reproducible than current conventional tests to detect viable spores. Viable spores could be reliably detected within two hours. The successful application of the Alamar Blue assay to measure fungal spore viability in the current study has important benefits for biosecurity operations relating to faster and more reliable confirmation of viability of potential invasive exotic fungal pathogens and in minimising any consequent disease outbreaks. The effectiveness of the Alamar Blue assay was confirmed by successfully determining the relative retention times of viable L. maculans ascospores across a range of different potential spore-carrier materials, including steel, fabric, wood, paper, rubber and leather, over a time period of eight months. To further confirm the wide applicability of the Alamar Blue assay, it was successfully applied to detect viable spores of fungal pathogens of diverse taxonomic groups, including Kabatiella caulivora, Magnaporthe oryzae and Puccinia striiformis f.sp. tritici, and also of the yeast Saccharomyces cerevisiae.
Stem rust caused by Puccinia graminis f.sp. tritici (Eriks & Henn.) is one of the most devastating diseases of wheat. If favorable conditions for the pathogen appear, the pathogen may cause both epidemics and pandemics. Evolution of genes of the pathogen population gives rise to emerge of new races of the pathogen. The Ug99 is a good example. In 1998, severe stem rust infections were observed on wheat in Uganda, and a race, designated as Ug99, was detected. The same race was detected in Kenya and Ethiopia in 2005. Later, Ug99 was established in Yemen in 2006, in Iran in 2007, in Tanzania and South Africa in 2009. The new race of stem rust has been seen globally as a threat to wheat production because Ug99 has spreaded from Eastern Africa to Middle East and Asia. In addition, scientists predict spreading of the pathogen towards other areas of the world through prevailed air currents. The situation is worrying for areas where wheat is grown.
Race Ug99 (TTKSK) of Puccinia graminis f. sp. tritici, detected in Uganda in 1998, has been recognized as a serious threat to food security because it possesses combined virulence to a large number of resistance genes found in current widely grown wheat (Triticum aestivum) varieties and germplasm, leading to its potential for rapid spread and evolution. Since its initial detection, variants of the Ug99 lineage of stem rust have been discovered in Eastern and Southern African countries, Yemen, Iran, and Egypt. To date, eight races belonging to the Ug99 lineage are known. Increased pathogen monitoring activities have led to the identification of other races in Africa and Asia with additional virulence to commercially important resistance genes. This has led to localized but severe stem rust epidemics becoming common once again in East Africa due to the breakdown of race-specific resistance gene SrTmp, which was deployed recently in the 'Digalu' and 'Robin' varieties in Ethiopia and Kenya, respectively. Enhanced research in the last decade under the umbrella of the Borlaug Global Rust Initiative has identified various race-specific resistance genes that can be utilized, preferably in combinations, to develop resistant varieties. Research and development of improved wheat germplasm with complex adult plant resistance (APR) based on multiple slow-rusting genes has also progressed. Once only the Sr2 gene was known to confer slow rusting APR; now, four more genes-Sr55, Sr56, Sr57, and Sr58-have been characterized and additional quantitative trait loci identified. Cloning of some rust resistance genes opens new perspectives on rust control in the future through the development of multiple resistance gene cassettes. However, at present, disease-surveillance-based chemical control, large-scale deployment of new varieties with multiple race-specific genes or adequate levels of APR, and reducing the cultivation of susceptible varieties in rust hot-spot areas remains the best stem rust management strategy.
Oxalic acid is an important virulence factor for disease caused by the fungal necrotrophic pathogen Sclerotinia sclerotiorum, yet calcium oxalate (CaOx) crystals have not been widely reported. B. carinata stems were infected with S. sclerotiorum and observed using light microscopy. Six hours post inoculation (hpi), CaOx crystals were evident on 46% of stem sections and by 72 hpi on 100%, demonstrating that the secretion of oxalic acid by S. sclerotiorum commences before hyphal penetration. This is the first time CaOx crystals have been reported on B. carinata infected with S. sclerotiorum. The shape of crystals varied as infection progressed. Long tetragonal rods were dominant 12 hpi (68% of crystal-containing samples), but by 72 hpi, 50% of stems displayed bipyramidal crystals, and only 23% had long rods. Scanning electron microscopy from 24 hpi revealed CaOx crystals in all samples, ranging from tiny irregular crystals (< 0.5 μm) to large (up to 40 μm) highly organized arrangements. Crystal morphology encompassed various forms, including tetragonal prisms, oval plates, crystal sand, and druses. Large conglomerates of CaOx crystals were observed in the hyphal mass 72 hpi and these are proposed as a strategy of the fungus to hold and detoxify Ca2+ions. The range of crystal morphologies suggests that S. sclerotiorum growth and infection controls the form taken by CaOx crystals.
A range of materials, including metals, fabrics, woods and plastics, were all effective carriers that maintain the long term viability of conidia and resting hyphae of the northern anthracnose pathogen of Trifolium species, Kabatiella caulivora. Conidia and hyphae became thick walled and melanised with time. There were significant (P<0.001) differences between carrier materials and between temperature regimes in terms of conidia/resting hyphae survival. At 23°C/4°C day/night, conidia and resting hyphae remained viable on steel, corrugated steel, galvanised steel and all tested fabrics, wood and random mixed materials for up to 8 months. At 36°C/14°C day/night, conidia and resting hyphae remained viable for up to 8 months, but only on cotton, denim, fleece, silk, leather, paper, plastic and all the wood materials. At 45°C/15°C day/night, conidia and resting hyphae remained viable up to 8 months, but only on fleece wool, Eucalyptus marginata (jarrah wood) and on paper. There were significant differences between carrier materials in their abilities to retain conidia and resting hyphae after washing (P<0.001). Metabolic activity was confirmed for conidia and resting hyphae recovered after 8 months and K. caulivora colonies successfully re-established on potato dextrose agar. Findings confirmed the critical importance of materials as long-term carriers of viable K. caulivora conidia and resting hyphae. Findings not only highlight the potential for spread of a highly virulent K. caulivora race inside and outside of Australia via farming equipment, clothing and other associated materials, but the wider biosecurity implications from the transportation of fungal-infested carrier materials previously considered as low-risk. This article is protected by copyright. All rights reserved.
The severity of the wheat stem rust problem in North America over-shadowed the effects of wheat leaf rust caused by Puccinia recondita in the early part of the 20th century. However, a major regional epidemic in 1938 throughout much of central United States on winter wheat emphasized its importance. Leaf rust primarily affects the leaf blades, whereas stem rust attacks the stem; thus, there is less time for a leaf rust epidemic development during the grain-filling period. Yield losses are usually less from leaf rust than from stem and stripe rust. Oat stem rust, like wheat stem rust, has been the most severe in the north central states and adjacent Canada. Crown rust is the most serious rust disease of oats in North America. Epidemics are common in the southern states, where the disease overwinters, and again on late seeded oats in Minnesota, the eastern Dakotas, and Manitoba. Crown rust is common in Mexico. Stem rust epidemics on barley develop more slowly than on wheat for a number of reasons that vary in importance with year and location.
Two-thirds of the world's total food supply is comprised of eight major cereal crops: wheat, rice, barley, rye, oats, corn, sorghum, and pearl millet. These crops may include more than one plant species, and the Food and Agriculture Organization (FAO) production statistics are often for total production. The millets are the most diverse group, being made up of several plant genera. In addition to the cereal crops, sugarcane is recognized as a major contributor to the world's food supply. Wheat and barley are grown primarily as temperate crops with a small area sown in the subtropics at present. A diverse virulence spectrum exists for both bread wheat and durum wheat. The leaf rust of wheat consistently causes some production losses but never as severe as the losses that are associated with stem rust. At present, the commercially grown spring bread wheat and durum wheat cultivars have adequate resistance to prevent severe losses. However, shifts in the virulence patterns of the pathogen continue to be of concern. Most winter wheat cultivars are at present susceptible to at least a part of the pathogen population.