S.38. Epidemiology of sunflower necrosis disease in Northern Karnataka

The necrosis virus disease is an important emerging constraint for successful sunflower production for the past five years in southern peninsular India and is caused by Tobacco streak virus (TSV). The disease is characterized by appearance of typical bud necrosis, chlorosis on leaves, stunted growth twisting of stem and appearance of necrotic lesions on petioles, stem and flower bracts and malformation of ear head with few or no seed development depending on the growth stage of crop at infection. The dates of sowing studies indicate least disease incidence was noticed during October to December sowing. The crop was free from the disease during October sowing. The progress of the disease during the cropping period was observed that the incidence was more at 60 days after planting and reached maximum at 80 days on crop growth. The maximum incidence of disease was correlated with weather factors indicating that the higher the temperature (31–33ºC) and decrease in relative humidity (77%) during the cropping period the higher incidence of the disease was noticed. The results were also indicated a higher negative correlation between minimum temperature (0.75**), morning relative humidity (0.75**) and evening relative humidity (0.52*). Multiple linear regression equation revealed that with every increase in one unit of maximum temperature the percent disease incidence was increased by 4.55 units. The weather factors influence up to 90% (r²= 0.9016). Step-down multiple linear regression equation indicated that with every increase in one units of minimum temperature the pre cent necrosis disease incidence was decreased by 21.63 units. The plot of percent disease incidence across days indicated a curvilinear response (Polynomial 3^rd order) with r² = 0.9577.