Heterosis for fruit yield, yield components and bacterial wilt resistance of tomatoes genotypes in Kenya

Yields of tomato (Solanum lycopersicum) in Kenya has continued to decrease due to biotic stresses especially bacterial wilt (Ralstonia solanacearum), fungal diseases, nematodes, tomato yellow leaf curl and overreliance on low yielding varieties such as UC82, Roma VF, Cal J and Riogrande. These problems stem from lack of a local breeding programme to develop new varieties suitable for fresh market and processing. The objectives of this study were to: i) determine heterosis for fruit yield, yield components and bacterial wilt in ten tomato lines; ii) select F1 hybrids combining resistance to bacterial wilt, high fruit yield, better shelf life and other market demanded traits, and iii) develop segregating F2 populations for further breeding. The parental lines included three elite breeding lines with resistance genes to bacterial wilt obtained from AVRDC-Taiwan, four local open pollinated commercial lines and three lines selected from tomato growers in central Kenya. The ten parental lines were crossed in a half diallele at Kabete Field Station, University of Nairobi in 2017. The 45 F1 and their parents were evaluated in the field at Kabete Field Station, Mwea Research Station, and in a bacterial wilt infested sick plot in Kanyei location, Kirinyaga County in 2018. Data were recorded on days to flowering, days to maturity, fruits per truss, fruits diameter, fruit length, fruits per plant, number of locules per fruit, average weight of fruit, resistance to bacterial wilt diseases. Bacterial wilt disease severity was scored on 0 to 5 scale (0=no disease symptoms, 1=one leaf wilted, 2=two leaves wilted, 3=three leaves wilted, 4=all leaves wilted except the tip, 5=entire plant dead) for two seasons in wilt infested sick plot in a farmer’s field in Kanyei location, Kirinyaga County and in a greenhouse at Kabete Field Station, both in Kenya. Results showed significant differences (P<0.05) for duration to 50% flowering, maturity, fruit diameter, fruit length, average fruit weight, number of fruits per plant, number of trusses per plant and fruit yield among the F1s and their parents. High parent heterosis -9% recorded on days to flowering (AVTO1429 x Cal J VF), -5% heterosis to maturity days (Roma VF x AVTO1314), 20% heterosis to plant height (AVTO1424 x UC82), 50% heterosis on vigour (AVTO1314 x Valoria select, AVTO1314 x Riogrande).