Disease impact and pathogenicity variation in Czech populations of Pseudoperonospora cubensis

摘要

Monitoring of Pseudoperonospora cubensis distribution and disease impact on cucurbits was conducted during 2001 (106 locations visited) and 2002 (134 locations visited) in the Czech Republic. Natural infection was observed only on cucumbers (Cucumis sativus), with other cucurbits were free of infection. On the majority of cucumber crops (63.2% in 2001, 64.6% in 2002) was observed a serious or very serious degree of infection (DI 3-4). A medium degree of infection was recorded on 25.5% of crops in 2001 and 32.8% in 2002. Other cucumber crops were characterized by low or no infection (11.3% in 2001, 2.6% in 2002). For determination of pathogenic variability were used a total of 96 P. cubensis isolates (42 isolates from 2001, 54 from 2002). Altogether,43 different pathotypes were detected (33 in 2001, 16 in 2002). In both years, a large.proportion of the screened isolates belonged to the group of highly pathogenic pathotypes (47.6% in 2001, 51.9% in 2002) and to the group of pathotypes with medium pathogenicity (47.6% in 2001, 48.1% in 2002). Only 2 isolates collected in the year 2001 expressed low pathogenicity. Race-specific interactions between Cucumis melo-P. cubensis and Cucurbita spp.-P. cubensis were observed.