SELECTION FOR HEAT TOLERANCE IN TOMATO Ex situ GERMPLASM

Abstract

In Egypt, the impact of high temperatures on tomato production during summer season has become an urgent issue. Where the day/night temperature rising above the optimal for flowering and fruit set, consequently, the fresh market tomato prices increase about 400 to 500% during this period with inferior quality of fruits. The objective of this work was to assay new genetic resources of a set of ex situ lines and cultivars for heat-tolerant. Furthermore, selection for promising parents that would be used in developing more adaptive cultivars to heat stress. All experiments were carried out during 2013 to 2015. Fifty tomato genotypes (Lycopersicon esculentum, Mill.) were evaluated in a randomized complete blocks design under the natural heat stress conditions. The following traits; plant height, number of branches, leave area, fruit set %, total chlorophyll, chl a/b ratio, chl T/carotenoid, in addition to yield and some fruit quality traits were estimated. Based on the phenotypic performance and the genetic divergence of these genotypes, 10 parental varieties were selected for a factorial mating design using 6 as males and 4 as females. High genetic variability was observed among the genotypes for all studied traits. Mean of fruit set % ranged from 12.7 % to 66.5%. Twelve genotypes gave more than 50kg/plot where the genotypes LA0535 and BGH-0226 recorded the highest mean values of 63.15 and 61.88 kg/plot, respectively. The mean squares of GCA as well as SCA were significant for the majority of studied traits indicting the importance of both additive and non-additive types of variation for all studied traits. Among the female lines, BGH-2004 exhibited maximum positive gi effect, while among the male lines, BGH-0226 displayed highest gi effect for plant height. The cross resulted from BGH-3474 x BGH-0226 gave the highest Sij effect for fruit set % indicating that the female line BGH3474 and tester BGH-0226 produced promising progenies for vegetative traits and fruit set improvement. While the female line BGH-3474 and male line BGH-7466 gave the highest gi effects for total yield per plot. According to the variation and diversity analysis, the genotype LA0535 from group I showed stable high yield across the two summer seasons 2014 and 2015 and was a good donor for fruit set, TSS and firmness however its poor fruit in lycopene. The hybrid 2x5 showed high adaptation against heat stress under field condition in 2015 with high total yield, leave area number of branches per plant, average fruit weight and fruit firmness but low lycopene. Therefore, for hybridization program, crosses among LA0535, BGH-0025, BGH-7466 for heat tolerance and yield could be effective and promising.