P.30. Investigations on papaya ringspot disease occurring in Tamil Nadu
Abstract
Papaya ringspot virus (PRSV), which was hitherto not prevalent in Tamil Nadu, has become a threat to papaya cultivation around Coimbatore. When healthy papaya seedlings of variety Co 2 raised in insect-proof conditions at glasshouse were mechanically inoculated at 4-leaf stage with the virus infected sap, typical symptoms of papaya ringspot disease viz., mottling and filiformity leaves were observed in 15- 20 days. Symptoms could be reproduced on papaya after back inoculation fulfilling Koch's postulates. The dilution end point of the virus was observed to be 10−4. Typical symptoms of oily streaks on upper parts of stem were observed after 50 – 60 days of inoculation. The virus produced chlorotic local lesions on Chenopodium quinoa. Leaf dip preparations from infected papaya samples revealed the presence of flexuous particles. Inoculations made at monthly intervals on healthy seedlings from December to October revealed that the symptom expression was dependent on environment and foliage symptom was favored by cloudy and cool weather. During fixed plot surveys the severity of the disease was found to be more on trees at the periphery of the orchard and less towards the centre. However, no aphid vector could be observed during monitoring. A scoring system, which takes into consideration the symptoms viz., chlorotic lesions, mosaic, filiformity of leaves and oily streaks on stem, has been developed in a 1- 3 scale to assess the severity of the disease in papaya germplasm, to locate sources of resistance.
