Investigation on the race composition of downy mildew (Plasmopara halstedii Farl. Berlese et de Tony) in Bulgaria during 2007-2008

Abstract

SUMMARY The climatic changes during the recent years and the general usage in the agricultural practice of resistant varieties and hybrids are the main reasons for the limited distribution of downy mildew on sunflower ( Plasmopara halstedii Farl. Berlese ét de Toni) in Bulgaria. The disease has occurrence only in separate locations, with a low percentage of attack - up to 10%. Our investigations showed that the current situation stimulated the pathogen to develop new races. Thus, for example, during 1988-2000, i.e ., over a period of 12 years, only two downy mildew races were identified in Bulgaria. Now, however, there are five: 300, 330, 700, 721, and 731. Race 700 has the largest area of occurrence. This race has been isolated from 20 samples with origin from northern Bulgaria during the years of investigation. Its percentage in the downy mildew population was 45.5%, and it is of the greatest economic significance for sunflower production in this part of the country. Races 721 and 731 were isolated in the last two years. They had equal percentages in the population - 15.9% each, but their area of occurrence was quite different. Race 721 was distributed in south-east Bulgaria, its range of occurrence was large, and it is the most significant race in this region in economic terms. The other new race, 731, was localized only in the region of the Dobroudja Agricultural Institute (DAI) and has currently no economic significance for sunflower production. Race 330 is also a new one for Bulgaria. It was isolated in 2006 in single fields in north Bulgaria and its percentage in the population was 13.6%. Race 300 had the most limited distribution during the last two years - 9.1%. This tendency has been observed for the last few years and most probably race 300 will soon disappear from the downy mildew population.