Growth Analysis for Studying the Effect of the Fungal Pathogen Diaporthe helianthi on the Achene Dry Matter Accumulation per Head in Sunflower Hybrids

Diaporthe helianthi Munt. Cvet. et al. (anamorph: Phomopsis) is a dangerous pathogen of sunflower, causing important yield losses. No information is as yet available, however, on the changes taking place in the achene yield-forming process, which eventually lead to the reduction in yield. The basic assumption was that by tracing the growth of the achene yield - using the growth analysis method - it would be possible to determine how the pathogenic fungus Diaporthe (=D.) helianthi - affected the dry matter accumulation process. The achene dry matter mass per head (ADM) was recorded at nine sampling dates during the achene filling period in five sunflower hybrids, in plants inoculated with the pathogen or treated with fungicide. Simultaneously with sampling, scoring was carried out for symptom dynamics. The results proved that, as the result of inoculation with D. helianthi, considerable changes took place in the achene dry matter accumulation process. The estimated growth characteristics of a second-order polynomial fitted to the ADM mass data: maximum yield per head (YMAX), average of absolute growth rate (AGRAVG), maximum of absolute growth rate (AGRMAX), maximum point of the absolute growth rate (XAGRMAX) and average of relative growth rate (RGRAVG), were considerably smaller in the inoculated treatment than in the sprayed treatment