The contribution of tomato and alternative host plants to tomato leaf curlvirus inoculum pressure in different areas of South India

Indian tomato leaf curl virus (ToLCV) (Geminiviridae: Sub-group III) was de tected both in field-collected and laboratory-reared B. tabaci using a trip le-antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA). ToLCV w as detected in six of the 10 group samples of field collected B. tabaci. To LCV was also identified in 13 weed species commonly found in Karnataka, bot h by symptom expression and TAS-ELISA. ToLCV from c. 61% of infected plants was transmitted successfully to tomato by B, tabaci. Tomato plots were planted at three locations on the University of Agricultu ral Sciences Campus, Bangalore. Indian tomato leaf curl virus disease (ToLC VD) incidence increased most rapidly when the tomato plot was situated adja cent to an older ToLCVD-infected tomato field. When the plots were position ed in a dryland or a wetland area, at least 500 m away from any infected to mato fields, the ToLCVD incidence increased less rapidly, although in all s ites it was 100% by 11 wk after transplanting. The numbers of B. tabaci cau ght on yellow traps in all sites increased during weeks 1-3 after transplan ting and thereafter remained at between 10-15 adults trap(-1) 24 h(-1). Adu lt numbers recorded on tomato plants by direct counts remained approximatel y constant at 2-4 adults plant(-1). Tomato fields were planted in three taluks (administrative areas) of Karnat aka, that had different current and previous histories of tomato production . ToLCVD incidence increased most and least rapidly, respectively, in Kolar taluk where tomato is grown continuously and Doddaballapur tuluk where tom ato was grown in the area for the first time. In Malur tuluk, where tomato was grown discontinuously (once a year), the incidence of ToLCVD increased at an intermediate rate. Weed host-plant species growing near the experimental sites had averages of between 1.5-10.0 B. tabaci nymphs per plant, whereas the tomato plants had only 0.3 nymphs per plant. The percentage parasitism of B. tabaci nymphs o n tomato and weed species, respectively, was 0.7% and 2-6%. Nymphs and pupa e were parasitised by an Encarsia sp. and Eretmocerus mundus Mercer. The relevance and implications of these findings for the epidemiology and m anagement of ToLCVD in Karnataka State, South India is discussed.