Estimates of Genetic Variance for Drought Tolerance Traits in Tomato

Tomato (Solanum lycopersicum L.) is an economically important vegetable crop worldwide and like many other crops, its productivity is severely impacted by environmental stresses such as drought. Genetic improvement through hybridization with wild relatives of the tomato is one approach of introducing important drought tolerant traits into cultivated varieties. Shoot and root morphological characteristics such as root mass/length, leaf size, root-to-shoot ratio, stomatal density and physiological properties such as stomatal conductance are important for drought tolerance. However, heritability of some of these tolerance traits is uncertain. In the current study, genetic variability and broad-sense heritability of an F2 population derived from a cross between a wild species Solanum cheesmaniae (with drought tolerance traits) and an advanced breeding line RVT1 were investigated. The F2 population, F1 and both parents were planted in sand media and morphological parameters: plant height, shoot fresh weight (SFW) and root length were measured after eight weeks. Significant phenotypic variation for all the traits was recorded among the F2 generation. Broad sense heritability in plant height, SFW, and root length were 0.90, 0.74 and 0.28 respectively, indicating strong genetic effects on plant height and SFW, compared to root properties. The unexpected amount of variation for root length among the F1 and parent plants may be an indicator of residual heterozygosity for underlying gene loci, as well as environmental effects. The occurrence of F2 progeny with root length and area greater than either parent demonstrates the potential of this approach for genetic improvement of drought stress tolerance.