This study was carried out to determine the incidence, prevalence, and variability of tomato viruses in tomato growing areas of Khyberpakhtunkhwa (KP) province and their management through host resistance. In summer tomato crop, the highest incidence of viral diseases of 60.7 percent was found in Malakand Agency followed by Peshawar with 49.04 percent, Charsadda with 46.1 percent, Mohmand Agency with 42.5 percent and Shabqadar with 41.3 percent incidence. The different viruses detected were Tomato mosaic virus ( ToMV), Potato virus X (PVX), Potato virus Y( PVY), Cucumber mosaic virus (CMV),Potato leaf roll virus ( PLRV), Tomato yellow top virus (TYTV) and Tomato yellow leaf curl virus (TYLCV). In winter tomato crop, the highest incidence of 52.74 percent was found in Charsadda, followed by Malakand Agency with 34.69 percent, and Mohmand Agency with 32.48 percent incidence. The different viruses detected were ToMV, CMV, PVX, PVY, PLRV, TYTV and TYLCV. In the third survey, the highest incidence of 36.0 percent was found in Shabqadar, followed by Peshawar with 28.0 percent, Charsadda with 27.0 percent, Mohmand Agency with 21.0 percent and Malakand Agency with 19.4 percent on the basis of symptomalogy. On the basis of ELISA, the highest incidence of 24.2 percent was found in Shabqadar, followed by Peshawar with 19.3 percent, Charsadda with 19.0 percent, Mohmand Agency with 15.2 percent and Malakand Agency with 14.6 percent.The incidence of tomato viruses infecting winter tomato crop in Mohmand Agency and Malakand Agency was 82.71 and 85.2 percent on the basis of symptomatology and 72.85 and 64.2 percent on the basis of ELISA. The different viruses detected were ToMV, PVX, PVY, CMV, PLRV, TYTV and TYLCV.For studying the characterization of prevalent isolates of ToMV, CMV and TYLCV, 25 isolates of ToMV and 20 isolates each of CMV and TYLCV were collected from the six major tomato growing areas of KPK and their biological properties were studied. The study revealed that ToMV population in KPK consisted of three pathological groups, the isolates in group-I caused severe symptoms on the test plants, the isolates in group-II caused mild symptoms and the isolates in group-III caused moderate symptoms in the host plants. The group-I isolate from tomato infected all hosts but the group-II isolate from okra did not infect tomato and tobacco, showing a difference in the host plants tested. Similarly, the CMV isolates comprised two pathological groups, the isolates in group-I were severe, whereas the isolates in group-II were mild. They also showed difference in the host plants infected. The tomato isolates in group-I infected all host plants but the onion isolates in group-II did not infect tomato. The isolates of TYLCV belonged to two pathological groups, group-I comprising severe isolates and group-II comprising mild isolates. The group-I isolates from tomato was transmissible to tomato but the pea isolates from group-II was transmissible to tomato and sarson only. Among the weather factors, temperature upto 25oC increased the population of whiteflies, whereas increase in relative humidity and precipitation decreased their population. Similarly increase in whiteflies population and their activities increased the incidence of TYLCV.Transmission properties of one aphid transmitted virus, CMV, and one whitefly transmitted virus, TYLCV, were investigated. The minimum time required for the acquisition and transmission of CMV were 10 minutes, the latent period was 20 minutes and the virus persisted in its vector, Myzus persicae, for a maximum of two hours, showing a non persistent type of transmission. Studies on the transmission properties of TYLCV revealed that, given an AAP of 24 hours, a single viruliferous whitefly had the capacity to transmit the virus, but for 100 percent transmission a minimum of five whiteflies per seedling were required. The minimum AAP and IAP were both 20 minutes.For 100 percent acquisition and transmission, a minimum of 10 hours were required. The latent period was five to seven hours. The virus persisted in its vector, Bemisia tabaci, upto 10 days after which the whiteflies were dead, indicating a persistent type of transmission. The effect of host plant resistance on the acquisition and transmission of the virus, using TYLCV-resistant tomato hybrid, T-1359, were investigated which revealed that host plant resistance decreased the time required for the acquisition and transmission of the virus. The AAP and IAP for resistant hybrid were both 48 hours, compared to AAP and IAP of 20 minutes for susceptible variety, Roma-VF. Among the thirty tomato varieties and germplasm hybrids studied for their resistance to ToMV and TYLCV, the hybrid, T-1359, was found to be highly resistant to both viruses. Two hybrids showed resistance, seven hybrids showed moderate resistance, one variety was susceptible and 19 varieties were highly susceptible to ToMV. Resistance to TYLCV was shown by five hybrids, moderate resistance by six hybrids and one variety, five varieties were susceptible and 12 varieties were highly susceptible.