Molecular and biological investigations of damping-off and charcoal-rot diseases in sunflower

Official URL: http://192.168.1.20/record=b1302949 (Table of Contents)

Sunflower (Helianthus annuus L.), is a major oilseed in both Turkey and Egypt as well as worldwide, two of the most important diseases of sunflower are damping-off and charcoal-rot. Damping-off is caused by the following pathogenic fungi: Fusarium oxysporum, Fusarium verticillioides, Rhizoctonia solani and Macrophomina phaseolina. Charcoal-rot, on the other hand, is incited by the soil inhabiting fungus Macrophomina phaseolina. Damping-off as well as charcoal-rot causes important economic loss in the main production areas of sunflower around the world. In this study we selected certain sunflower fields from Egypt and Turkey to collect the fungi associated with the roots of sunflower plants so as to isolate the causal pathogens of damping-off and charcoal-rot. The isolated fungi were able to infect sunflower plants under artificial infection and cause the symptoms of pre- and post- emergence damping-off as well as charcoal-rot. To our knowledge, this is the first report of M. phaseolina in sunflower in Turkey. We performed the first study with sequence related amplified polymorphism (SRAP) for an overview of genetic diversity and phenetic relationships present among the isolates of Macrophomina and Fusarium. Results showed that Turkish and Egyptian isolates of M. phaseolina were clustered together with a genetic similarity of 60%; similarly, Turkish and Egyptian isolates of F. oxysporum were clustered together with a genetic similarity of 75%. Infection reactions of 41 sunflower cultivars for infection with charcoal-rot disease were also evaluated. Results indicated that certain sunflower cultivars are resistant to charcoal-rot, but the most cultivars are susceptible. A relationship between root exudates and the mechanism of sunflower plant resistance to charcoal-rot and damping-off was found. The application of biological control agents, under greenhouse conditions, significantly reduced plant mortality and increased surviving plants. These agents can readily be used to gain more resistance to charcoal-rot disease in sunflower.