ARS | Publication request: Application of a new approach for characterization and denomination of races of cucurbit powdery mildews – a case study on the Czech pathogen population

Submitted to: Eucarpia Cucurbitaceae Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 20, 2012
Publication Date: October 15, 2012
Citation: Lebeda, A., Sedláková, B., Krístková, E., Vajdová, M., McCreight, J.D. 2012. Application of a new approach for characterization and denomination of races of cucurbit powdery mildews – a case study on the Czech pathogen population. In:Sari, N., Solmaz, I., Aras, V., editors. Cucurbitaceae 2012, Proceedings of the Xth EUCARPIA meeting on genetics and breeding of Cucurbitaceae, October 15-18, 2012, Antalya, Turkey. p. 172-180.

Technical Abstract: Golovinomyces cichoracearum (Gc) and Podosphaera xanthii (Px) (Ascomycetes, Erysiphaceae) are the most important fungal species causing cucurbit powdery mildew (CPM), a serious disease of field and greenhouse cucurbits. Both species are highly variable, as indicated by the existence of large number of different pathotypes and races (Lebeda et al. 2011; McCreight, 2006). Various independent systems of CPM pathotype and race determinations and denominations have been used worldwide. Lebeda et al. (2008) critically reviewed the current state, gaps, and perspectives in our understanding of pathogenicity variation in these two CPM pathogens at the pathotype and race levels. They proposed two sets of differential cucurbit genotypes for the identification of CPM pathotypes and races, and an objective, efficient, uniform and comprehensive coded system for meaningful, concise designation of CPM pathotypes (sextet code) and races (septet code). Race diversity among and within 18 Czech CPM (6 Gc, 12 Px) isolates collected in 2010 from Cucurbita pepo (56%), Cucurbita maxima (28%), Cucurbita moschata (11%) and Cucumis melo (5%) was characterized using the set of 21 C. melo–CPM race differentials proposed by Lebeda et al. (2008) and previously described experimental procedures (Lebeda and Sedláková, 2010). Development of CPM infection varied substantially among the 21 differentials. Twelve differentials (Iran H, ‘Védrantais’, PI 179901, AR Hales Best Jumbo, ‘PMR 45’, PI 414723, ‘PMR 5’, PI 313970, PI 236355, ‘Amarillo’, ‘Nantais Oblong’, ‘Solartur’) were highly susceptible (78-100% interactions exhibited compatible reactions). Four differentials (WMR 29, ‘Negro’, ‘Edisto 47’, ‘Noy Yizre’el’) expressed intermediate frequencies of compatible reactions (44-67%). In contrast, moderately low frequencies of compatible reactions (22%) were observed on two differentials (PI 124112, MR-1), and low (6%) on two other differentials (PI 234607, ‘PMR 6’). One differential, PI 124111, was 100% resistant to the screened isolates. The 18 CPM isolates were grouped according their level of pathogenicity (i.e. number of susceptible differential genotypes): high (4; 22% of isolates), medium (13; 72%) and low (1; 6%). Seventeen races were identified using the triplet septet code among 18 of the CPM isolates (6 Gc, 12 Px). One race (Gc 55.63.119) occurred twice; the other 16 races (4 Gc and 12 Px) occurred once. Diversity of CPM races among the 17 isolates from 2010 verified previous observations of Czech CPM populations (Lebeda et al., 2007, 2011; Lebeda and Sedláková, 2006), and confirmed that Czech CPM populations are unique, and highly variable in race structure. The new set of 21 differentials and septet code revealed and characterized more completely race variation within and among CPM populations.