Diallel analysis involving heat-tolerant lines of tomato.

Abstract

The critical factor in setting of tomato fruits is night time temperature, the optimum range being 15- 21°C. Fruit set in tomato is reduced markedly when average maximum day time and minimum night time tem- peratures go above 32 and 21°C, respectively. In the northwestern plains of India, temperature crosses the favor- able limit from the fourth week of April onwards, thereby reducing yield, lowering quality and shortening the fruit harvest span. The situation has forced tomato breeders to develop heat-tolerant cultivars and, therefore, the present study was conducted to determine the nature of gene action controlling various characters and to iden- tify a few good combiner genotypes that may be used in further breeding programmes for high temperature tol- erance. Highly significant general combining ability (gca) and specific combining ability (sea) variances indicat- ed the importance of both additive and non-additive gene action in the expression of all the characters. Howev- er, the ratio of components of genetic variance revealed the predominant role of non-additive gene actions in con- trolling total yield, marketable yield, number of fruits per plant, average fruit weight, days from fruit setting to turning stage, endosperm utilization efficiency, harvesting span, pericarp thickness, number of locules, lycopene content and titratable acidity. Therefore, heterosis breeding may be used to bring improvement in these traits. However, additive gene action played a major role in controlling days to anthesis, number of flowers per cluster and setting percentage per cluster. Hence, lines having good gca for these traits (LST-6, LCT-9, LST-42-1 and LST-65-2) may be hybridized and selection may be practiced in segregating generations to develop advanced gen- eration lines having high heat-tolerance ability.