GENOTYPIC AND ENVIRONMENTAL VARIATION IN A BC₂ OF L. ESCULENTUM X L. CHEESMANII FOR SOLUBLE SOLIDS AND FOR YIELD CHARACTERS

Soluble solids content (SSC) is one of the most important quality characters in processing tomatoes. It is a polygenic (quantitative) character largely influenced by water application and other environmental factors. Yield has also an important environmental influence. The environmental influence difficults the selection for soluble solids content and yield in segregating generations when every plant is genotypically different from the others. A method to measure and control environmental influence could be to grow a number of replicates of each genotype. In this work, fifty-four seeds from a BC₂ of Lycopersicon esculentum x L. cheesmanii f.minor to L esculentum were in vitro propagated to obtain at least nine genetically identical plants per seed. From every set of nine plants, three of them were cultivated by drip irrigation without water stress. three by gravity irrigation without water stress, and three by gravity irrigation with water stress. Marketable fruit production, average fruit weight, SSC (°Brix) and pH were measured on every plant.

Marketable yield and average fruit weight with drip irrigation (5270 g/plant and 51.9 g) were significantly higher than with gravity irrigation without stress (3699 g/plant and 43.7 g) or with gravity irrigation with water stress (3610 g/plant and 43.1 g). Although water stress showed no influence in yield, it significantly increased soluble solids from 5.5 °Brix in drip irrigation and in gravity irrigation without stress to 6.1 in gravity irrigation with water stress. Genotypic variance with respect to the total variance was 56% for average fruit weight, 40% for SSC and about 26% for yield and pH. Variance due to the irrigation systems used was lower than genotypic variance: 18% for yield, 12% for average fruit weight and 22% for SSC and pH, while the variance of the interaction was 18% for yield. 5% for average fruit weight, 8% for SSC, and 2% for pH. The low value of the genotype x irrigation system interaction for fruit weight and SSC indicates that selection for these characters could be carried out in any of the three irrigation systems used independently of the irrigation system usually employed by growers. The relatively high heritabilities in broad sense found for fruit weight (0.63) and for SSC (0.52) indicate that environmental influence can be effectively controlled by phenotipical estimation of those characters in several copies (9 in our experiment) of the same genotype.