Category Archives: Wiley: Plant Pathology

Alternaria brassicicola‐induced ROS accumulation during black spot disease differentially affects antioxidant efficiency, phenolic content and susceptibility of Brassica species

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Alternaria brassicicola-induced ROS accumulation during black spot disease differentially affects antioxidant efficiency, phenolic content and susceptibility of Brassica species

Alternaria brassicicola triggers reactive oxygen species generation, causing black spot disease, following diverse patterns of antioxidative enzyme activity in susceptible Brassica juncea, B. napus and B. oleracea.


Abstract

Early-stage responses of Brassica juncea, B. napus and B. oleracea during black spot disease and the development of Alternaria brassicicola were evaluated. Infection of plant cells by the fungus occurred mainly through direct penetration or by appressoria and, rarely, stomata in B. juncea and B. oleracea; in B. napus, penetration was mostly direct. The process of conidial germination, germ tubes and appressoria formation on a leaf surface was correlated with the post-inoculation time and host species (p < 0.05). Changes in the leaf surface were observed at successful infection sites as bright, wax-deprived areas. Significant differences in progression of infection between Brassica species were observed, with B. oleracea being the most susceptible and B. napus the least. Accumulation of superoxide anion radicals and hydrogen peroxide was not only observed in plant cells, but also in A. brassicicola germ tubes and appressoria at 8 and 12 h post-inoculation (hpi). Enhanced production of reactive oxygen species (ROS) and lipid peroxidation during infection triggered diverse patterns of enzymatic and non-enzymatic antioxidant activities and phenolic compound contents in response to A. brassicicola. In each Brassica species, a different antioxidant was the most active. With their antioxidant properties, phenolic compounds also played an essential role in these interactions. This phenomenon could be related to the disparate levels of susceptibility of the Brassica species to A. brassicicola; for example, the most susceptible, B. oleracea, showed high ROS accumulation with decreasing tendency during disease progression, unchanged phenolics content, and the highest catalase activity, differentiating it from B. juncea and B. napus.

Hunting for sources of durable resistance in crop cultivar evaluation data: The case of wheat yellow rust in France

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Hunting for sources of durable resistance in crop cultivar evaluation data: The case of wheat yellow rust in France

Trajectories of field adult plant resistance ratings to yellow rust in 719 French wheat cultivars between 1963 and 2018 suggest the presence of effector-triggered and/or quantitative resistance.


Abstract

Cultivar resistance is a major asset for the management of crop diseases and can play an important role in agroecological transition. However, the wide deployment of a reduced number of resistance genes can lead to a rapid adaptation of pathogen populations and to a loss of resistance efficiency. The objective of this study was to characterize and discuss different trajectories of adult plant ratings for resistance to yellow rust in French wheat cultivars between 1963 and 2018. Among 719 cultivars assessed for at least 2 years, 590 cultivars showed no variation in their resistance scores, despite a mean of 4.3 years and up to 33 years of assessment. A set of descriptive variables was computed in order to compare the evolution of resistance score of 129 cultivars that experienced resistance variation. We applied a principal component analysis and a hierarchical clustering on principal components to this subdataset to constitute clusters corresponding to different cultivar profiles. Clusters C1 and C2 had small resistance variations (1–2 points on a 1–9 scale); Cluster C3 had long assessment durations and several small drops in resistance score and could be associated with quantitative resistance erosion; Cluster C4 included major drops in resistance score (4–5 points), often associated with known breakdowns of major resistance genes. Cases of limited drops in resistance score as a known resistance gene was broken down suggest the presence of efficient adult plant resistance. We discuss the use of information extracted from this dataset and methods to further explore sources of resistance to yellow rust present in French cultivars.

Ergot of cereals: Toxins, pathogens and management

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Ergot of cereals: Toxins, pathogens and management

This review article focuses on recent progress in understanding the toxins, pathogens and management of ergot, an important disease of cereals that affects food safety.


Abstract

Ergot is a fungal disease of many plants but is perhaps most commonly associated with domesticated grasses or cereals, such as rye, wheat, barley, oat, sorghum, millet, maize and rice. Ergot is of historical significance, having been reported for several millennia, but is also of concern in modern agricultural production systems. Caused by many different species within the genus Claviceps, the fungi cause the production of sclerotia, which are typically dark in colour, in place of healthy grain. The sclerotia contain toxins that can make the grain unsafe for consumption by humans or livestock. Ergot can be managed both preharvest as well as postharvest to minimize the presence of sclerotia and their associated toxins in food and feed systems. In this review, we provide a detailed update on our current knowledge of ergot on cereals, with a focus on recent advances in our understanding of fungal toxins and their regulation, pathogen biology and disease management.

Predicting airborne ascospores of Sclerotinia sclerotiorum through machine learning and statistical methods

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Predicting airborne ascospores of Sclerotinia sclerotiorum through machine learning and statistical methods

Across all statistical and machine learning models, the greatest predictor of ascospores released on a given day was the number of ascospores released on the previous day.


Abstract

A main biological constraint of dry bean (Phaseolus vulgaris) production in Canada is white mould, caused by the fungal pathogen Sclerotinia sclerotiorum. The primary infectious propagules of S. sclerotiorum are airborne ascospores and monitoring the air for inoculum levels could help predict the severity of white mould in bean fields. Daily air samples were collected in commercial dry bean fields in Alberta, Manitoba and Ontario and ascospores were quantified using quantitative PCR. Daily weather data was obtained from in-field weather stations. The number of ascospores on a given day was modelled using 63 different environmental variables and several modelling methods, both regression and classification approaches, were implemented with machine learning (ML) (random forests, logistic regression and support vector machines) and statistical (generalized linear models) approaches. Across all years and provinces, ascospores were most highly correlated with ascospore release from the previous day (r ranged from 0.15 to 0.6). This variable was also the only variable included in all models and had the greatest weight in all models. Models without this variable had much poorer performance than those with it. Correlations of ascospores with other environmental variables varied by province and sometimes by year. A comparison of ML and statistical models revealed that they both performed similarly, but that the statistical models were easier to interpret. However, the precise relationship between airborne ascospore levels and in-field disease severity remains unclear, and spore sampling methods will require further development before they can be deployed as a disease management tool.

Clavibacter tessellarius causing bacterial mosaic of wheat establishes in the Old World

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Clavibacter tessellarius causing bacterial mosaic of wheat establishes in the Old World

Using field surveys and samplings we confirmed widespread occurrence of the wheat pathogen Clavibacter tessellarius in southern Iran and establishment of the bacterium in the Old World.


Abstract

The genus Clavibacter (family Microbacteriaceae) includes gram-positive actinobacterial species infecting diverse agricultural crops such as alfalfa, maize, pepper, potato, tomato and wheat. Clavibacter tessellarius, causing bacterial mosaic of wheat, was reported for the first time in 1976 in Nebraska (United States). Since then, the pathogen was thought to be restricted to North America (Canada and the United States). While bacterial strains suspected to be C. tessellarius have occasionally been isolated from wheat samples outside North America, occurrence of the pathogen in the Old World has not yet been confirmed by the plant protection authorities. In spring 2020 (January to May) dozens of wheat fields with young plants showing leaf chlorosis and mild mosaic symptoms were surveyed and sampled in southern Iran. Among 192 surveyed wheat fields, gram-positive, orange-pigmented actinobacterial strains were isolated from samples of 53 fields. Altogether, 61 bacterial strains were identified as C. tessellarius based on the phenotypic features, PCR-based molecular tests and pathogenicity assays. Multilocus sequence analysis of five housekeeping genes (atpD, dnaK, gyrB, ppk and rpoB) using 10 representative strains from diverse geographic areas in southern Iran confirmed the phylogenetic status of the strains within C. tessellarius. Our data indicate that the bacterial mosaic pathogen occurs in four southern Iranian provinces including Bushehr, Fars, Kerman and Khuzestan. Thus, occurrence of C. tessellarius outside North America is confirmed. Potential risks associated with the emergence of the pathogen in the Old World, and the need for strict quarantine measures in the area, is further discussed.

Survey of Phyllosticta citricarpa mating type in the São Paulo citrus belt and optimization of in vitro ascospore production

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Survey of Phyllosticta citricarpa mating type in the São Paulo citrus belt and optimization of in vitro ascospore production

The two mating types of Phyllosticta citricarpa occurred in similar ratio in the São Paulo citrus belt; ascospores were produced in potato dextrose agar (PDA), ½ PDA and malt extract agar (MEA) at 15, 20 and 25°C, especially in MEA at 25°C.


Abstract

Phyllosticta citricarpa, the citrus black spot causal agent, requires both mating types, designated as MAT1-1 and MAT1-2, to produce ascospores. Mating-type ratio in some citrus-growing areas has been characterized but remains little known in the São Paulo (SP) citrus belt, the largest sweet orange producer worldwide. A protocol for in vitro ascospore production was developed recently; however, there are few studies regarding the optimal conditions for their production. Thus, this study aimed to determine the mating-type ratio in SP and quantify ascospores produced under different conditions in vitro. The mating types were identified by duplex PCR, and ascospore production was assessed in five culture media: potato dextrose agar (PDA), ½ PDA, malt extract agar (MEA), oatmeal agar (OMA) and citrus agar (CA), and at temperatures from 10 to 30°C. The ratio of MAT1-1 and MAT1-2 was similar to 1:1. Ascospore production reached peaks of 8.0, 7.0 and 3.0 × 103 ascospores/mL in MEA, PDA and ½ PDA, respectively. There were no ascospores observed in OMA and CA. P. citricarpa ascospores were observed only at 15, 20 and 25°C in PDA, with peaks of up to 2.0 × 103 ascospores/mL at 42, 35 and 21 days, respectively. There were no ascospores observed at 10 and 30°C. Both mating types are similarly distributed in the SP citrus belt, and in vitro ascospore production may be optimized by using MEA at 25°C. These data provide a better understanding of P. citricarpa sexual reproduction and a background for further studies with ascospores.

Genome‐wide association study of adult plant resistance to spot blotch in an elite Canadian two‐row barley germplasm collection

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Genome-wide association study of adult plant resistance to spot blotch in an elite Canadian two-row barley germplasm collection

Using elite Canadian two-row barley germplasm, GWAS identified several single-nucleotide polymorphism (SNP) molecular markers of multiple chromosomes that were associated with adult-plant resistance to Bipolaris sorokiniana.


Abstract

Spot blotch, caused by Bipolaris sorokiniana, is a growing concern for barley (Hordeum vulgare) production in most humid, temperate growing regions of the world. Under epidemic conditions, this disease can reduce yields significantly. Reduction of kernel plumpness is associated with lower malt extract and consequently grain quality. Enhanced resistance to this disease is a major goal of western Canadian two-row barley breeding programmes; however, two-row barley is considered to be more susceptible than six-row barley. Plant–pathogen interactions observed for Canadian germplasm are polygenic, where quantitative breeding methods could be beneficial for the development of resistant germplasm. A germplasm panel consisting of 200 two-row, spring barley genotypes with differential reaction to spot blotch was evaluated at Brandon, Manitoba (MB), and Melfort, Saskatchewan (SK), over eight site years. Genome-wide association study was conducted using a 50k single-nucleotide polymorphism (SNP) Illumina iSelect genotyping array. The most-resistant germplasm was found to carry Midwest Six-rowed Durable Resistant Haplotype (MSDRH) alleles at the loci located on chromosomes 1H (Rcs-qtl-1H-11_10764), 3H (Rcs-qtl-3H-11_10565) and 7H (Rcs-qtl-7H-11_20162, Rcs5 locus), where the 3H locus was found to be the most under-represented in Canadian germplasm. Additional marker-trait associations within nurseries were identified on chromosomes 1H, 2H and 4H. Several of the SNP markers identified were found to be polymorphic within the Canadian two-row germplasm panel and thus could be useful for enhancing spot blotch resistance in two-row barley for development of resistant cultivars.

Morphology, phylogeny and pathogenicity of fungal species associated with leaf blight and stem canker of Theobroma cacao in Malaysia

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Morphology, phylogeny and pathogenicity of fungal species associated with leaf blight and stem canker of Theobroma cacao in Malaysia

Leaf blight of Theobroma cacao in Malaysia was found to be caused by Diaporthe tulliensis and Neopestalotiopsis clavispora while stem canker was caused by D. tulliensis, Fusarium proliferatum and Fusarium solani.


Abstract

Malaysia stands prominently among Asia's key cocoa-producing countries. In the cocoa season of 2022–2023, Malaysia demonstrated its contribution to the industry, with an estimated production of around 364,000 tonnes of cacao bean grindings. Nonetheless, fungal diseases pose undeniable challenges to the cocoa sector. Extensive sampling conducted between September 2018 and March 2019 across multiple states in Malaysia revealed concerning symptoms of leaf blight and stem canker affecting Theobroma cacao plants. The aim of this study was to identify and characterize fungal species associated with leaf blight and stem canker of T. cacao in Malaysia through morphological, molecular and pathogenicity analyses. Morphological and molecular phylogenetic analyses using multiple DNA regions (rDNA internal transcribed spacer [ITS], TEF1 and TUB2) were performed and identified 40 fungal isolates found in this study as Diaporthe tulliensis (17 isolates), Fusarium solani (seven isolates), Fusarium proliferatum (six isolates) and Neopestalotiopsis clavispora (10 isolates). Pathogenicity tests with mycelial plugs and wound treatments showed that D. tulliensis and N. clavispora were responsible for causing leaf blight whereas D. tulliensis, F. solani and F. proliferatum caused stem canker of T. cacao. The present study provides insights into disease aetiology and symptomatology that may be useful in planning effective disease management for the host plant.

The pathogenic diversity and host range of Colletotrichum spp. causing pepper spot and anthracnose of lychee (Litchi chinensis) in Australia

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The pathogenic diversity and host range of Colletotrichum spp. causing pepper spot and anthracnose of lychee (Litchi chinensis) in Australia

Pathogenicity on lychee and population genomics show that taxa in the gloeosporioides species complex are predominantly clonal, and symptoms and host range are linked to genotype.


Abstract

Lychee pepper spot, a field disease affecting lychee fruit skin, pedicels and petioles, is caused by Colletotrichum siamense, a fungal pathogen within the gloeosporioides species complex. Members of Colletotrichum from the gloeosporioides species complex and occasionally those from the acutatum species complex also cause postharvest anthracnose of lychee. Pepper spot was first described in Australia many years after anthracnose on lychee was first described, giving rise to the hypothesis that a novel species or strain within the gloeosporioides species complex causes pepper spot. In the present study, 19 isolates of Colletotrichum spp., collected from pepper spot and anthracnose symptoms on lychee fruit, representing 13 different genotypes across five species, were inoculated onto lychee fruit in the field or on detached fruit in the laboratory, to understand more about their pathogenic diversity. We found that symptoms were specific to genotype of the pathogen, as three genetically similar isolates of C. siamense consistently caused pepper spot and anthracnose, whilst other isolates caused anthracnose only. Cross-inoculation studies on detached fruit of lychee, banana, avocado and mango also provided some evidence of host specialization in isolates of C. siamense infecting lychee in Australia. Our experiments provided further evidence that detached fruit assays cannot be used as a reliable proxy for field inoculation studies. This research confirms that C. siamense is a causal agent of both lychee pepper spot and lychee anthracnose in Australia, and Colletotrichum alienum and Colletotrichum queenslandicum are reported as causal agents of anthracnose of lychee for the first time.