BYADGI, A SHALAKERI, ANAND V2019-10-172019-10-171999No . of references 72http://krishikosh.egranth.ac.in/handle/1/5810131718Sunflower necrosis disease, causing considerable damage to the crops, is a serious disease and present in almost all parts of Northern Karnataka wherever sunflower in grown. Affected plants were characterized by production of mosaic and chlorotic ringspots. In extreme cases the affected leaves developed marginal necrosis with reduction in leaf size. In later stage of disease development, affected plants produced mgdformed head and seeds of poor quality. The virus causing necrosis disease in sunflower was sap transmissible but not with ease. It was not transmitted through seeds and dodder. The virus was transmitted by thrips (Thrips fabad) vector from sunflower to sunflower and to tomato. But not by aphids, jassids and whiteflies. The virus had a narrow host range and infected only 3 plant species among 15 different hosts tested belonging to 6 families. The virus had DEP between 10 ^ to 10^, TIP between 35° to 40°C and retained infectivity upto 2 hours at room temperature. Based on symptoms, host range, transmission and physical properties, it was concluded that the sunflower necrosis disease in this area, is probably caused by member of Tomato spotted wilt virus (Tospovirus) group. In early infected crop (15 days after sowing) the disease had a severe effect on yield and yield parameters. The disease reduced yield of sunflower to a tune of 90.86 percent when appeared in early stage of the crop growth as compared to 31.69 percent when appeared late. Field trials indicated that the spread of the disease could be minimized by spraying Imidacloprid (0.025%) insecticide. None of the 56 sunflower hybrids screened were resistant to virus infection, but hybrid UH-32 and 7 others exhibited some tolerant properties.ennullThesis