Diagnostics,genetic diversity and pathogenic variation of ascochyta blight of cool season food and feed legumes |
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Authors: | Paul W J Taylor Rebecca Ford |
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Institution: | (1) Centre for Plant Health/BioMarka, School of Agriculture and Food Systems, Faculty of Land and Food Resources, The University of Melbourne, Parkville, Melbourne, VIC, 3010, Australia |
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Abstract: | Molecular diagnostic techniques have been developed to differentiate the Ascochyta pathogens that infect cool season food and feed legumes, as well as to improve the sensitivity of detecting latent infection
in plant tissues. A seed sampling technique was developed to detect a 1% level of infection by Ascochyta rabiei in commercial chickpea seed. The Ascochyta pathogens were shown to be genetically diverse in countries where the pathogen and host have coexisted for a long time. However,
where the pathogen was recently introduced, such as A. rabiei to Australia, the level of diversity remained relatively low, even as the pathogen spread to all chickpea-growing areas.
Pathogenic variability of A. rabiei and Ascochyta pinodes pathogens in chickpea and field pea respectively, appears to be quantitative, where measures of disease severity were based
on aggressiveness (quantitative level of infection) rather than on true qualitative virulence. In contrast, qualitative differences
in pathogenicity in lentil and faba bean genotypes indicated the existence of pathotypes of Ascochyta lentis and Ascochyta fabae. Therefore, reports of pathotype discrimination based on quantitative differences in pathogenicity in a set of specific genotypes
is questionable for several of the ascochyta-legume pathosystems such as A. rabiei and A. pinodes. This is not surprising since host resistance to these pathogens has been reported to be mainly quantitative, making it difficult
for the pathogen to overcome specific resistance genes and form pathotypes. For robust pathogenicity assessment, there needs
to be consistency in selection of differential host genotypes, screening conditions and disease evaluation techniques for
each of the Ascochyta sp. in legume-growing countries throughout the world. Nevertheless, knowledge of pathotype diversity and aggressiveness within
populations is important in the selection of resistant genotypes. |
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Keywords: | Diagnostics Genetic diversity Pathotypes Ascochyta Cicer Lens Pisum Vicia |
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