Dobroudja Agricultural Institute, BG-9250 General Toshevo, Bulgaria
ENTCHEVA, V., 2002. Variation in the aggressiveness of isolates from Phomopsis/Diaporthe helianthi Munt.-Cvet. et al. in sunflower. Bulg. J. Agric. Sci., 8: 349–352
Phomopsis/Diaporthe helianthi Munt.-Cvet. et al. is a pathogen causing gray spots on sunflower (Helianthus annuus L.) and leads to considerable yield decrease. The use of resistant hybrids and varieties is the most efficient economically justifiable means for control of the pathogen. The existing variation in the aggressiveness of the pathogen isolates, however, impedes the selection of resistant plasma. This paper presents data on the response of nine sunflower hybrids to eight isolates of Phomopsis/Diaporthe helianthi Munt.-Cvet. et al. collected from different regions of Bulgaria. Plants were inoculated at stage beginning of flowering by the straw-method. Results were read ten days after infection. The area of the lesions on the plant stems was measured. Among the eight isolates studied, isolate DZI had the highest aggressiveness. The least aggressive was isolate Bogorovo. The other six isolates showed moderate aggressiveness. The response of the hybrids was closely related to the aggressiveness of the isolates. A statistically significant interrelation of genotype x isolate was established.