First report on the occurrence of a new pathotype, 714, of Plasmopara halstedii (sunflower downy mildew) in Hungary.
Downy mildew of sunflower, caused by Plasmopara halstedii, is an economically important disease in Hungary and much of Europe. There are at least 36 pathotypes of P. halstedii worldwide, but the number of races is increasing rapidly. In 2010, race 704 was identified in Hungary for the first time. Race 704 has been reported to confer virulence on Pl6, a broad spectrum resistance gene that is widely used in sunflower hybrids. This has coincided with a significant increase in disease severity since 2010 in the country. A study was conducted to continuously monitor this pathogen and identify pathotypes of P. halstedii. Because of the unfavourable weather conditions for downy mildew in 2013, samples were collected at a single site (Kunszentmárton, South Hungary) in the beginning of July from NK Neoma sunflower hybrids. Disease incidence (early and late primary infection) was as high as 40%. Systemically mildewed plants showed severe stunting and leaf chlorosis, signs and symptoms consistent with downy mildew. P. halstedii was identified microscopically. Examination of isolates was carried out using a set of sunflower differential lines based on the internationally standardized method for race identification of P. halstedii. Evaluation of a single isolate that caused as high as 100% infection on HA-335, containing resistance gene Pl6, resulted in an aggregate virulence phenotype of 714. This is thought to be the first report of pathotype 714 of P. halstedii in both Hungary and Central Europe.