THE EFFECTS OF HEAD ROT DISEASE (Rhizopus stolonifer) ON SUNFLOWER GENOTYPES AT TWO DIFFERENT GROWTH STAGES

Head rot caused by Rhizopus stolonifer reduces sunflower seed yield and quality. The objective of this study was to determine the effects of head rot disease on seed yield in eight sunflower cultivars. The sunflower cultivars were inoculated by R. stolonifer at two different growth stages (R5.7 and R6.0) of sunflower. The results revealed that mechanical or physical damage on back of sunflower head results in infection of the head rot disease and significantly reduced the seed yield. The differences among the cultivars were significant for disease severity. The results also significantly varied with growth stages for seed yield of the cultivars. In addition, the cultivars showed significant differences in terms of their responses to R. stolonifer at both two growing stages. As a result, mechanical damages on back side of the plant head cause significant increase in disease severity and yield losses in sunflower.