Independent and Combined Effect of Genotype and Some Agronomy Factors on Yield and Phomopsis helianthi Infection in Sunflower
II. Effect on Phomopsis helianthi Infection

Dobroudja Agricultural Institute, BG-9520 General Toshevo, Bulgaria


ENCHEVA, V., T. K. TONEV and P. YANKOV, 2003. Independent and combined effect of Genotype and some agronomy factors on yield and Phomopsis helianthi infection in Sunflower. II. Effect on Phomopsis helianthi infection. Bulg. J. Agric. Sci., 9: 615–620

The response of three sunflower hybrids (Albena, Santa Fe and Diamant) to the attack by the cause agent of gray spots Diaporthe/Phomopsis helianthi Munt-Cvet. et al., was studied by investigating the effect of the following agronomy factors: Main type of soil tillage (ploughing at 20–22 cm and disking at 10 cm); Nitrogen fertilization (N0 and N60 against background of P60K0); Density of growing (45 000, 55 000 and 65 000 plants/ha). It was established that the Phomopsis severity was strongly affected by the genotype of the sunflower plant. Hybrid Santa Fe was attacked with less severity than hybrid Albena both after ploughing and disking. Hybrid Diamant showed considerably higher susceptibility to the cause agent of grey spots with regard both to the other hybrids and the type of soil tillage. The main soil tillage type specifically affected the number of plants attacked by increasing or restricting the effect of the other agronomy factors. Nitrogen fertilization of sunflower increased the susceptibility of the crop to Phomopsis helianthi. The increased crop density lead to increasing the number of the infected plants; this was most evident in hybrid Albena.

Key words: Phomopsis helianthi, genotype, soil tillage, nitrogen rate, crop density