Study on aggressiveness to isolates of Phomopsis/Diaporthe helianthi Munt. Cvet. et al. on sunflower under field conditions

Mariya Petrova, Nina Nenova, Valentina Encheva

Abstract: Phomopsis or Sunflower gray spot with telemorph Diaporthe helianthi and anamorph Phomopsis helianthi is one of the economically important diseases of sunflowers worldwide. Losses caused by the pathogen reach 40% of productivity, and in oil content - 15-20%. The use of resistant hybrids is considered the most effective measure to control the disease. The established aggressive variation in pathogen populations creates significant difficulties in the breeding process. Therefore, the aim of the present study was to determine the aggressiveness of Diaporthe helianthi isolates with a view to their further use as markers in the breeding of resistance to the fungus. The study included 30 isolates of the fungus from four agro-ecological areas in Bulgaria. The aggressiveness of the isolates was established under field conditions, by artificial inoculation of the Deveda hybrid and the Favorit variety using the Straw-method. The inoculation was carried out at the beginning of flowering, and the results were reported after 14 days on a 9-point scale. Based on the score, the Area Under Disease Progress Curve (AUDPC) for each genotype was calculated, as well as the Avarage Area Under Disease Progress Curve for both genotypes (AAUDPC). A highly significant influence of genotype and isolate, as well as their interaction (P<0.0001), was found. Six of the studied isolates showed high aggressiveness towards the Deveda hybrid. Nine of the studied isolates showed high aggressiveness in relation to the Favorit variety. Isolate 29 (21-211) (AAUDPC=52.0), followed by isolate 6 (21-6212) are characterized by the highest aggressiveness compared to the studied genotypes, and the differences in values are not significant. Variation in the aggressiveness of the isolates was observed in each of the production areas, with the aggressiveness of the isolates of Karnobat origin being below the average of all studied.

Keywords: aggressiveness; Diaporthe; Phomopsis, isolates; sunflower

Date published: 2023-08-24