Resistance Components to Bacterial Spot Race T2 (Xanthomonas vesicatoria) in Tomato Genotypes Under Greenhouse and Growth Chamber Conditions

Abstract

Bacterial leaf spot is one of the main diseases affecting tomato crops. The causative agents are four species of the Xanthomo-nas genus. In Uruguay, the prevalent species is Xanthomonas vesicatoria race T2. Due to the lack of effective control measures, genetic resistance acquires great interest to improve disease management. This research was conducted in order to identify resistance sources to bacterial leaf spot race T2 in tomatoes based on resistance components under greenhouse and growth chamber conditions. Latent period, number of spots in the terminal leaflet, and the bacterial population in the tissue were the components were evaluated. In addition, leaf spot severity was determined by a diagrammatic scale. Cultivars Hawaii 7981 and Loica, as well as the lines LB 76 and LB 97 were the most resistant genotypes displaying the lowest leaf severity, number of leaf lesions, and bacterial population. The leaf spot number, as well as the bacterial population, allowed differentiating genotypes by bacterial spot resistance under controlled conditions. However, latency period did not differ significantly between genotypes. The cultivars Loica and Hawaii 7981 were identified as new sources of partial resistance to race T2.