RESPONSE OF SOME POPULAR CASSAVA VARIETIES TO MOSAIC VIRUS AND TWO MAJOR SUCKING PESTS UNDER FIELD CONDITIONS IN TAMIL NADU, INDIA
Surveys were undertaken in intensive cassava growing areas of Salem, Namakkal and Dharmapuri districts of Tamil Nadu adopting fixed plot survey method for five consecutive years (2010-15) to observe the response of some popular cassava varieties to cassava mosaic disease (CMD) and two important sucking pests namely spiralling whitefly (Aleurodicus dispersus Russell) and papaya mealybug (Paracoccus marginatus). Significant differences in the incidence of CMD were noticed among different varieties. Kunguma rose was found to have highest incidence of 95.68 % @ ten months after plantation (10 MAP) followed by H226 (91.20%), MVD1 (85.69%), H165 (47.51%) and CO(TP)4 (37.73%). Lowest incidence of 27.09 & 28.52 % was observed in CO2 and CO3 and thus exhibited tolerance to the disease. Infestation of spiralling whitefly started during the months of April-May i.e. @ 4-5 MAP and the population increased in relation to increase in plant age leading to severe incidence @ 10 MAP in October. Highest population per leaf (17.08) @ 10 MAP was recorded on MVD1 followed by H226 (15.37) and Kunguma Rose (13.98). The lowest population (8.12) was recorded on CO2 variety. The incidence of papaya mealybug was started @ 1 MAP and the severity in population build up increased with plant maturity. Highest population per leaf (97.95) was recorded on H226 followed by MVD1 (96.62), H165 (93.51), Kunguma Rose (92.60), CO3 (89.08), CO(TP)4 (85.42) and CO2 (81.15) @ 10 MAP. Based on the survey results it can be concluded that the cassava varieties resistant to CMD, spiralling whitefly and papaya mealybug should be preferred for cultivation to avoid the frequent damage and losses. Further, information generated under this study could help to pay more attention to set up timely management strategies.
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