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

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.

Rotating and stacking genes can improve crop resistance durability while potentially selecting highly virulent pathogen strains

“…However, crop resistance can be circumvented by adaptation of the pathogen if the same type of resistance is deployed over several years, as occurs with Leptosphaeria maculans populations (stem phoma canker—Blackleg disease) 20 , 21 . Shifts in pathogen species and virulence diversity 22 , 23 can also lead to resistance breakdown. This also includes the development of new pathogen pathotypes, such as occurs with other Brassicaceae pathogens like Sclerotinia sclerotiorum 24 , Hyaloperonospora brassicae 25 , Albugo candida 26 , Neopseudocercosporella capsellae 27 and, Alternaria spp.…”

Novel synergistic fungicidal mixtures of oxathiapiprolin protect sunflower seeds from downy mildew caused by Plasmopara halstedii

“…Berl. and de Toni is a devastating disease of sunflower ( Helianthus annuus L) worldwide [1–3]. SDM has been reported from over 50 countries [4] except Australia and New Zealand.…”

“…SDM has been reported from over 50 countries [4] except Australia and New Zealand. First epidemics in cultivated sunflower were reported in the US in 1890, nearly 50 years before the first records of the pathogen were reported in Europe [3]. The long distance dispersal of SDM almost certainly occurred through the exchange of oospore-contaminated seeds [5, 6].…”

“…Oospores are the indispensable key element for overwintering in the soil and for long distance dispersal via seed contamination [5–7]. In particular, the uncontrolled exchange of oospore-contaminated seeds is a major reason for the nearly worldwide distribution of the pathogen since the middle of the 20 th century [3].…”

Understanding Host–Pathogen Interactions in Brassica napus in the Omics Era

“…From the pathogen perspective, the availability of the multi-omics data is useful for screening candidate pathogenicity genes in the pathogen. However, this is dependent upon the race classification keeping pace with the omics data of the fungal/oomycete pathogens becoming available; otherwise, an effective application of the pathogenicity genes in field populations cannot be achieved [ 229 ].…”