Effect of virulence and methods of inoculation on the incidence of Alternaria helianthi leaf blight in Sunflower

An intensive survey conducted in different parts of sunflower growing areas of Tamilnadu showed a maximum incidence of 72 percent disease index (PDI) in Narnapuram of Tirunelveli district. Therefore, in the present study, the influence factors such as, effects of virulence, methods of inoculation, age and susceptibility of the plants on the disease incidence was evaluated. Virulence of different isolates collected from different parts of Tamilnadu during the survey was confirmed by artificial inoculation. Narnapuram isolate I₃ was found to be the most virulent with 70.22% disease incidences. Best results were obtained in the expression of typical symptom with spore injection method (74.22 PDI) as compared to the pinpricking coupled with spore spray method (46.67 PDI). In the case of age and susceptibility of sunflower plants, 70 day old plants were highly susceptible which showed a significantly high PDI (72.22%), while a minimum PDI (13.00%) was recorded in 20 day old plants