Viruses infecting winter tomato crops in the North West Frontier Province of Pakistan

Abstract

Malakand Agency is a unique production area in the North West Frontier Province (NWFP) of Pakistan that is frost-free and in which tomato is grown as a winter crop. Tomato production in this area has been affected by virus-like diseases for the last 10 years. Tomato nurseries and fields at 11 locations in Malakand Agency were surveyed for tomato viruses during 1994–95. A total of 1071 samples from nurseries and 5083 samples from 142 fields were tested by indirect enzyme-linked immunosorbent assay (ELISA). In nurseries, 3 viruses, Potato virus X (PVX), Potato virus Y (PVY), and Tomato mosaic virus (ToMV), were detected with an incidence range of 9.8–22.3, 0–36.6, and 16.5–51.3%, respectively. In the field, 5 viruses [Cucumber mosaic virus (CMV), PVX, PVY, ToMV, and Tomato yellow top virus (TYTV)] were frequently found with an incidence range of 0–13.3%, 2.6–16.7%, 0.4–13.8%, 26.1–41.3%, and 1.7–11.3%, respectively. All 5 viruses except TYTV were also detected from weed species in tomato fields or in the nearby vicinity. Of 12 commercial tomato varieties screened against CMV, PVX, PVY, and ToMV, 2 varieties (Florist and Forset) were resistant to 4 of the viruses including ToMV, for which the highest incidence was recorded in nurseries and field. These 2 varieties represent a previously undescribed and potentially useful source of resistance to the 4 inoculated viruses.