Firmness of tomato fruits depends on trait accumulation and incorporation of the ripening inhibitor gene

Nowadays tomato selection includes firmness and shelf-life of fruits. Tomato selection for these traits has to include selection for pericarp thickness, firmness of epidermis and firmness of flesh. Fruit firmness is a polygenic trait and depends on firmness components. Fruit firmness can be increased by accumulating favourable traits of each component. This paper deals with aspects of increasing fruit firmness by increasing firmness of the epidermis and thickness of the pericarp. By using genotypes with the rin (ripening inhibitor) gene, we were able to accomplish high fruit firmness, especially firmness of flesh. The expression of these traits causes asynchronization of the maturing process so the fruits do not over-mature or soften. Genetic effects have been evaluated by researching the average values of fruit firmness in six diallel parent lines (D-150, S-49, S-35, H-52, Kg-z and SP-109) and progeny (P-1, P-2, F-1, F-2, BC1, and BC2) by applying an additive dominant model with three and six parameters. Mean values of fruit firmness for parents and progeny were significantly different. Firmness of fruits was influenced primarily by additive genes. Dominant gene effects appeared in certain cross combinations. Epistatic gene effects were important in inheritance for all three two-gene interactions. The stable duplicate type of epistasis was found, which in this case reduces the unfavourable effects of dominant parent genes.