Genetic studies on the inheritance of disease resistance, fruit yield and quality in tomatoes (Lycopersicon esculentum Mill)
Interspercific crosses involving the wild tomato variety Cherry, Lycopersicon esculentum var. cerasiforme and the commercial cultivars; NR1, NR 2, NR 44 and NR 46 were made. Vegetative characteristics, disease resistance and fruit qualities of the F1, F2, B1 and B2 generations were studied. Days to visible bud stage, number of branches per plant at anthesis, plant height, number of flowers per truss, number of fruits per truss, days to maturity, average fruit diameter, average fruit weight, total fruit weight, number of fruits per plant, total fruit yield, disease reaction were the characters studied. Diseases encountered in the field included damping-off, seedling blight, wilt, die back and viral diseases. In general, Cherry was found to be highly tolerant to many diseases and to drought when compared to the commercial parents. With the exception of seedling blight, which was observed to be controlled by duplicate dominant epistatic genes since the F2 ratio of healthy to diseased plants was 15:1, other fungal diseases were observed to be controlled by a single dominant gene since the F2 ratio of healthy to diseased plants was 3:1. F, hybrids were observed to be as good as the Cherry in disease tolerance and vigour. Cherry had higher mean values than the NR-lines for all the characters except average fruit diameter, average fruit weight and total fruit weight per plant. The hybrids especially F1, B1, B2 and some F2 were observed to be close to the wild Cherry in most of the characters. The major problem with the use of Cherry in these crosses was on the size of the fruits which was below marketable size. However, fruit size of F1s was improved through the use of commercial cultivars as donor parents (males) in a backcross to produce B2 progenies. Fresh fruits picked at colour break and stored in the laboratory to fully ripen stage were analysed for pH, soluble solids contents, citric acid, total sugars, vitamin C and colour. Cherry had higher soluble solids content, total sugars, citric acids and vitamin C than the commercial cultivars and its colour was as good as the other genotypes. All these qualities were passed on to the progenies. Heritability (in narrow sense) estimates for the vegetative, yield and fruit quality traits were high indicating that all these traits influenced by additive genes and as such progress can be made through selection for such traits. In order to develop stable varieties with high disease tolerance, acceptable fruit sizes and good fruit quality, it is suggested that single plant selection followed by backcrosses using the commercial varieties as recurrent parents may be followed.
A thesis submitted to the Crop Science Department, College of Agriculture and Natural Resources, Kwame Nkrumah University Of Science & Technology, Kumasi, in partial fulfilment of the requirements for the Master of Philosophy Degree in Plant Breeding, 2000