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Original Articles

Biological Characteristics and Assessment of Virulence Diversity in Pathosystems of Economically Important Biotrophic Oomycetes

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Abstract

Plant biotrophic oomycetes cause significant production problems and economic losses in modern agriculture and are controlled by fungicide applications and resistance breeding. However, high genetic variability and fast adaptation of the pathogens counteract these measures. As a consequence of the “arms race,” new pathogen phenotypes recurrently occur and may rapidly dominate the population when selected through the pressure of control measures. Intensive monitoring with fast and reliable identification of virulence phenotypes is essential to avoid epidemics and the economic consequences in agriculture. For some of the most important downy mildews and white blister rusts, bioassay-based differentiation has been established to classify infectivity of field isolates or cultivated strains on hosts of defined resistance. However, the testing is laborious, time-consuming, logistically demanding, and prone to impreciseness. Alternatively, host independent classification could overcome these problems and enable fast assessment of the infection risk when monitoring the local pathogen population. The prerequisite would be the identification of pathogen characters correlating with the infection behavior. This review examines the current situation of bioassay-based pathotyping in six of the most important biotrophic oomycetes (Plasmopara viticola, Plasmopara halstedii, Pseudoperonospora cubensis, Peronospora tabacina, Bremia lactucae, and Albugo candida) and gives an overview on attempts and progress to identify genetic markers of the pathogens that correlate with their infection behavior.

Acknowledgements

The authors thank Dr. Yigel Cohen for the critical review of the manuscript before submission. A. Lebeda work was supported by projects MSM 6198959215 (Ministry of Education, Youth and Sports), QH 71254 and QH 71229 (Czech Ministry of Agriculture), and by the Internal Grant Agency of Palacky University in Olomouc (IGA_PrF_2019_04). R. N. Trigiano's contribution was supported by USDA Grant NACA 58-6062-6.