Inheritance of yield and quality characteristics in processing tomatoes

English: The main objective of this study was to determine the combining ability of several tomato genotypes, the heritability of various yield and quality characteristics and the expression of heterosis in the F1 hybrids. 2. Six inbred tomato genotypes were used as parental lines in the diallel cross. Crosses were made in glasshouses at the University of the Orange Free State. The F1 hybrids and their parental lines were planted at the ARC - Roodeplaat Vegetable and Ornamental Plant Institute. Various yield and quality characteristics were analysed. 3. Significant differences among the six parental lines were recorded for total yield, marketable yield, green yield and average fruit mass. The 15 F1 hybrids showed significant differences for total yield, marketable yield, unmarketable yield, green yield and average fruit mass. 4. Significant genetic variation among the SIX parental genotypes was recorded for fruit pH. The 15 F1 hybrids show no significant differences for soluble solid content and fruit pH. 5. A significant positive phenotypic correlation (r=0.95) was found between total yield and marketable yield. 6. Inbred line p88/120 was the best general combiner for most of the yield characteristics while p88/120 and p88/192 is the best general combiners for most of the quality characteristics. Crosses p881l40 x UC82B, P881l20 x p88/192 and p881l40 x p881l92 were the best specific combiners for total and marketable yield. The best specific combination was the cross between p88/164 and UC82B, which had 7 positive SCA values. 8. A GCA:SCA ratio of 85:1 was recorded for average fruit mass indicating that additive genes are involved. 9. Narrow sense heritability were relatively high for average fruit mass (H2n= 74.38%), green yield (H2n=55.01 %) and fruit colour (H2n= 50.04%). The breeder can select effectively for larger fruited genotypes as well as selecting against green yield to increase the total yield. 10. The average level of heterosis over the best parent exceeds 10% for total and marketable yield between all the F1 hybrids. Heterosis of the F1 hybrids over mid-parent value (Hmp), heterosis over the better parent (Hbp) and superiority over the best parent (Scm) was mostly negative for all the quality characteristics.