Tomato Breeders Roundtable 2001 1

Introduction The whitefly Bemisia tabaci Genn. (Homoptera:Aleyrodidae) has caused millions of dollars worth of crop losses in tropical and subtropical agricultural regions in the five continents of the world (Brown, 1994). Besides the direct damage caused by B. tabaci (plant nutrient loss; physiological disorders; honey dew excretions, etc), the sweet potato or cotton whitefly is an efficient vector of numerous geminiviruses (plant viruses consisting of two ‘twined’ or ‘geminate’ particles, encapsidating one or two single -stranded DNA genomes). The geminiviruses transmitted by B. tabaci belong to the genus Begomovirus (sigla for the type species, Bean golden mosaic virus), according to current taxonomic classification (Regenmortel et al., 2000). These viruses infect a large number of cultivated plant species, following their transmission by B. tabaci from wild or other cultivated hosts (Padidam et al., 1999). Currently, over 100 begomoviruses are transmitted by at least two biotypes of the whitefly B. tabaci, to more than 20 different cultivated species of socioeconomic importance. The main food crops affected by whitefly-transmitted geminiviruses are: common bean, mung bean, blackgram, lima bean, soybean, cowpea, tomato, potato, eggplant, pepper, chili peppers, melon, watermelon, squash, okra and cassava (Muniyapa, 1980; Brown, 1994). The extreme pathogenicity and severe yield losses induced by begomoviruses, and absence of immune genotypes in most of the plant species attacked, has led to considerable pesticide abuse in order to control the whitefly vector. As a result, B. tabaci has developed resistance to most of the insecticides used in the past.