Evaluation of Tomato (Lycopersicon Esculentum Mill.) Genotypes for resistance to the Tomato Yellow Leaf Curl Tanzania Virus

Abstract

Field experiments were conducted for two seasons (2001 and 2002) to determine the reaction of tomato genotypes to Tomato yellow leaf curl Tanzania virus. Tomato plants at the first leaf stage were inoculated with the virus in insect-proof cages in the screenhouse following 48-h and 72-h acquisition and inoculation feeding times by Bemisia tabaci, respectively. After inoculation, the whiteflies were killed with Karate 5EC (a.i 50 g/l λ-cylohalothrin). Test plants were transplanted to the field 4 weeks after inoculation in paired inoculated and non-inoculated plots replicated three times. The plants were maintained insect-free for the duration of the experiment by spraying weekly with Karate 5EC. Disease severity was scored weekly on a scale of 0 – 4 (0 = no symptoms and 4 = very severe symptoms). Average fresh plant weight after harvest (without roots), fruit number per plant, fruit weight and average total yield were recorded. There were significant differences in the effect of disease on yield components between genotypes compared with uninfected controls, except for genotype TY172, which produced insignificant differences (P = 0.5) in all the parameters assessed between the inoculated and uninoculated control plants. The susceptible cultivar Moneymaker had the most severe symptoms of TYLCTZV of all the cultivars tested, while no symptoms were observed on the resistant tomato line TY172. The line TY172 consistently performed better than the rest of the tomato genotypes, followed by Tengeru 97. Tengeru 97 produced the highest mean plant fresh weight and yielded more than the rest of the tomato genotypes tested. It is therefore, suggested that the resistance found in TY172 should be introgressed into Tengeru 97, Cal-J and Moneymaker, which are local tomato varieties preferred by growers in Tanzania. Such efforts will increase and improve the yield and quality of these varieties.