First Report on the Occurrence of a New Pathotype, 714, of Plasmopara halstedii (Sunflower Downy Mildew) in Hungary

Abstract

Downy mildew of sunflower, caused by Plasmopara halstedii (Farlow) Berlese et de Toni, is an economically important disease in Hungary and much of Europe. The known pathotypes (races) of the pathogen influence the resistance genes (Pl genes) incorporated into new sunflower hybrids to manage the disease. There are at least 36 pathotypes of P. halstedii worldwide (3), but the number of races is increasing rapidly. In 2010, race 704 was identified in Hungary for the first time (2). 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. Our objectives are to continuously monitor this pathogen and identify pathotypes of P. halstedii. Because of the unfavorable 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 (1). Inoculum of the isolates was increased on a susceptible cultivar (cv. Iregi szürke csíkos) and tested by inoculating 3-day-old seedlings of sunflower differential lines. Inoculated seedlings were planted in trays in glasshouse. After 8 to 9 days, seedlings were sprayed with distilled water, covered with black plastic bags, and left overnight to induce sporulation. Disease incidence was determined by examining cotyledons at 9 days after inoculation for sporulation and true leaves on 12 to 13 days after inoculation for secondary symptoms, such as leaf chlorosis and stunting (1). While several differential lines showed no typical susceptible/resistant reactions, i.e., the infection was much lower than 100%, it was concluded that the isolates were mixtures of different P. halstedii pathotypes. To obtain single isolates, we collected zoosporangia from the differential lines in question separately, and then inoculated the seedlings of the same genotype and a uniformly susceptible line. A single isolate caused as high as 100% infection on HA-335, containing resistance gene Pl6. Subsequent evaluation of this isolate with the entire differential set resulted in an aggregate virulence phenotype of 714. As resistance gene Pl6 is incorporated to the majority of sunflower hybrids grown in Hungary, pathotypes virulent on this gene, such as 704 and 714, are likely to spread. This underscores the need to prove the resistance to these races in the newly registered hybrids and for further research to identify P. halstedii pathotypes. It is also important to establish the identity of this new pathotype by already discovered 714 pathotypes in other countries like France and Italy and to discover the real conditions of local evolving of new pathogens. To our knowledge, this is the first report of pathotype 714 of P. halstedii in both Hungary and Central Europe. References: (1) T. J. Gulya et al. Helia 14:11, 1991. (2) K. Rudolf et al. Növényvédelem 47:279, 2011. (3) F. Virányi and O. Spring. Eur. J. Plant Pathol. 129:207, 2011.

Pathogenic variability of Plasmopara halstedii infecting sunflower in the Czech Republic

“…In the last years of the survey, four races, 70471, 71461, 70571 and 71571, were detected with high virulence complexity which overcome Pl 6 and even Pl 15 genes. Beside these results, new occurrences of races 704 and 714 have been reported from Hungary (Bán et al ., ,) as well as a recent prevalence of race 714 in France (Virányi et al ., ).…”

“…In 2007 the global number of P. halstedii races reached 36 (Gulya, ), 24 of which were reported in North America, 20 in Europe, 10 in Africa, and 5 races in both South America and Asia. In the following years, new races were found in Europe; 721 and 731 that were discovered in Bulgaria during 2007/8 (Shindrova, ), race 704 (Bán et al ., ) and 714 (Bán et al ., ) in Hungary and race 774 in France (Gascuel et al ., ). Recently, Virányi et al .…”

New and High Virulent Pathotypes of Sunflower Downy Mildew (Plasmopara halstedii) in Seven Countries in Europe

“…The first high virulent pathotype (704) was isolated in 2010 by Rudolf et al [ 22 ] from two sunflower fields in Hungary. In the following years, our research team confirmed the increased distribution of pathotype 704 in the country [ 27 ] and the emergence of three new P. halstedii pathotypes, 714, 724, and 734 [ 13 , 14 , 28 ] (New records are separated from previously published records by bold isolate numbers in Table 3 .). Previously, pathotype 724 was only identified from Hungary, but according to our present results, it was also detected in Romanian samples in 2019.…”

Methodology of virulence screening and race characterization of Plasmopara halstedii, and resistance evaluation in sunflower – a review

“…Downy mildew on cultivated sunflowers was first recorded in the USA in the 1920s (Young & Morris, ). Cultivation of open‐pollinated sunflower varieties that were highly susceptible to Ph, both in Europe and North America, helped the rapid spread of the disease (Virányi, ; Sedlářová et al ., , ; Bán et al ., ; Anonymous, ; Virányi et al ., ) and caused several severe outbreaks (Zimmer, ; Göre, ). Therefore sunflower downy mildew has been declared a quarantine pathogen in the European Union since 1992 (Delmotte et al ., ).…”