First Report on the Increased Distribution of Pathotype 704 of Plasmopara halstedii in Hungary

Abstract

Downy mildew of sunflower caused by Plasmopara halstedii (Farlow) Berlese et de Toni is a devastating disease worldwide. The treatment of seeds with fungicides and the use of resistant cultivars are widely employed control measures against this oomycete. Effective protection, however, may be hindered by the high genetic variability of the pathogen. There are 14 pathotypes of P. halstedii in Europe and as many as six of these were identified in Hungary before 2010 (1,4). In 2010, a new race, 704, was isolated in the eastern region of Hungary (3). Although the new pathotype was identified in two sunflower fields (near Vészto and Kondoros), it was expected to spread all over the country because of a lack of resistance against this race. The aim of our study, therefore, was to monitor the distribution of pathotype 704 in Hungary. Infected sunflower plants (2 to 5 samples/site) showing typical symptoms of downy mildew (leaf chlorosis, severe stunting) from four different sites (Árpádhalom, Rákóczifalva, Tiszasüly, and Újiráz) in the eastern region of the country were collected in mid-June 2012. 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 (2). Inoculum of 17 isolates was increased on a susceptible cultivar (cv. Iregi Szürke Csíkos). Leaves containing zoosporangia were washed off in distilled water. The concentration of spore suspension for each isolate was adjusted to 20,000 to 30,000 viable zoosporangia per ml using a hemacytometer. Pre-germinated seeds of sunflower differential lines (20 seeds/line) with an optimal radicle length were selected and placed in separate petri dishes. They were filled with freshly prepared zoosporangial suspension of the isolates and incubated in the dark at 16°C for 6 h. Inoculated seeds were planted in trays. After 8 to 9 days when the first true leaves were ~0.5 to 1 cm long, the trays containing the plants were covered with transparent plastic bags overnight. Distilled water was sprayed into the bags to ensure a humid environment for stimulating sporulation. First disease assessment was performed immediately after incubation based on the appearance of characteristic white sporulation on cotyledons. A second evaluation was made of true leaves of 21-day-old plants. Twelve out of 17 isolates were pathotype 704, infecting either one of two commercial sunflower hybrids (NK Neoma and NK Brio) or volunteer sunflower plants. The remaining five isolates were races 700, 710, and 730, which are known to be widespread in Hungary (1). The presence of race 704 was proven in all sampling sites representing the eastern part of the country. This finding underscores the need to develop and grow improved sunflower hybrids with effective genes against this pathotype. To our knowledge, this is the first report of the wider distribution of pathotype 704 of P. halstedii in both Hungary and Central Europe. References: (1) T. J. Gulya. Adv. Downy Mildew Res. 3:121, 2007. (2) T. J. Gulya et al. Helia 14:11, 1991. (3) K. Rudolf et al. Növényvédelem 47:279, 2011. (4) F. Virányi and S. Maširević. Helia 14:7, 1991.

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 .…”

“…Over the years, 17 races have been determined in French populations (Gascuel et al ., ). Pathogen variability has also been intensively studied in Hungary (Bán et al ., ,), Spain (Molinero‐Ruiz et al ., ), Bulgaria (Shindrova, ), Germany (Rozynek & Spring, ), Italy (Tosi & Beccari, ) and Russia (Ivebor & Antonova, ).…”

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.…”

New data on pathotype distribution and mefenoxam tolerance of Plasmopara halstedii in Hungary

“…With the increase in the cultivation area of sunflower production in the 2000s in Hungary, downy mildew became more widespread and has recently been considered as one of the most important pathogens of sunflowers. One of the reasons for the increased significance of the disease is the occurrence of new pathotypes in some regions in Europe (and in Hungary, too) after 2010 (Bán et al 2014a(Bán et al , b, 2018Trojanová et al 2018). Another reason may be the decreasing sensitivity of the P. halstedii strains to mefenoxam.…”