The inheritance and genetic expression of the ripening inhibitor (rin) gene in tomato

English: 1. The objective of this study was to determine the combining ability of several tomato genotypes, the correlation and heritability between several yield and quality characteristics and the expression of heterosis in the hybrids. 2. Six parental lines and three testers were used in a Line x Tester analysis. Crosses were made in glasshouses at the University of the Free State (UFS). The F1 hybrids and their parental lines were planted in glasshouses at the UFS with three replications. Several yield and quality characteristics were measured ,§lndanalysed. 3. Significant differences were found between the parents for all characteristics measured. Significant differences were recorded between crosses, except for unmarketable yield. KOM 1 x RIN 1 ranked first for total and marketable yield, while the parental line, RIN 3, ranked first for shelf life. Significant differences were found between the lines, except for unmarketable yield, average fruit size and sugar-content (day 16). Significant differences were found among the line x testers, except for unmarketable yield, fruit pH (day 1,4 and day 12) and sugar-content (day 1, 8 and day 20). 4. The parental line KOM 1 proved to be the best general combiner for both total and marketable yield, while F1B was the best general combiner for average fruit mass, average fruit size and shelf life. Parental line R 1 was the best general combiner for fruit pH and sugar-content over the different days. 5. Crosses F1B x RIN 1, RDP 1 x RIN 2 and KOM 2 x RIN 3 were the best specific combiners for total and marketable yield, while RDP 1 x RIN 2 was also the best specific combiner for average fruit mass and average fruit size. KOM 2 x RIN 2 proved to the best specific combiner for the quality characteristics as it had the most positive effects followed by KOM 1 x RIN 1. 6. The specific combining ability (SCA) variance of the study was found higher than the general combining ability (GCA) variance for all the traits except for sugar-content. This means that a large part of the total genetic variability sugar-content. This means that a large part of the total genetic variability was the result of non-additive gene action. 7. Marketable yield showed a significant positive genetic correlation with total yield and average fruit size with fruit mass. Shelf life showed negative genetic correlations for all the traits, except for average fruit size. 8. All the traits had low broad-sense and very low narrow-sense heritabilities. Marketable yield (h²n = 0.06) had the highest narrow-sense heritability for the yield characteristics and fruit pH (h²n = 0.08) the highest for the quality characteristics. 9 Eleven hybrids expressed positive mid-parent (MP) heterosis and five hybrids expressed positive high-parent (HP) heterosis for total yield. KOM 1 x RIN 1 expressed the highest mid-parent and high-parent heterosis for total yield and marketable yield. Fruit pH had the most hybrids with positive midparent (16) and high-parent (12) heterosis. Heterosis was mostly negative for all the quality characteristics measured, thus indicating the effect of the environment.