Heterosis and Combining Ability for Bacterial Wilt Resistance, Fruit Yield and Shelflife of Tomato in Kenya

Abstract

Tomato accounts for 7% of total horticulture production and 14% of vegetables produced in Kenya. Despite its importance, tomato has not received much research attention. Unlike the leading tomato producers, Kenya has no tomato breeding program, hence the reliance on imported seeds. In addition, strategies for management of major diseases such as bacterial wilt that cause up to 100% yield loss are limited. The specific objectives of this study were to: (i) identify suitable parental lines for population development from new accessions and local genotypes; (ii) screen parental lines and their F1 hybrids for resistance to bacterial wilt; iii) determine the inheritance for agronomic, bacterial wilt resistance, and fruit yield traits.; iv) determine the heterosis and combining ability for agronomic traits and fruit yield, and v) determine the shelf-life of parental lines and their F1 hybrids. Objective 1 trials were conducted in a randomized complete block design with three replicates in two seasons starting 2017. Study materials were AVTO1429, AVTO1424, AVTO1314, four commercial varieties and three farmer selections. Genotypic effects, genotypic x environment interactions and location effects for days to flowering, plant height, maturity, fruit yield and related traits were highly significant (P<0.01). Duration to flowering varied from 36 to 42 days; plant height from 66.37 to 182.57cm, duration to maturity from 85 to 100 days, and fruit yield from 18.3 to 55.7 t ha-1. All the genotypes showed determinate growth habit except AVTO1314 with indeterminate. AVTO1429, AVTO1424 and AVTO1314 had green stem while the commercial varieties and farmers’ selection had purple stem. Trials for objective 2 were conducted at field and greenhouse conditions for two seasons from 2017. The potted media in the greenhouse was inoculated with 107 CFU/ml Ralstonia solanacearum suspension. Results showed wilt incidence varied from 11.87% for AVTO1424 to 89.87% for Roma VF. Lowest wilt incidence of 11.87, 12.29 and 13.53% were recorded in lines AVTO1424, AVTO1429, and AVTO1314, respectively. Wilt incidence among the 45F1 hybrids varied from 7% in cross AVTO1429 x AVTO1314 to 90% in cross Eden Select x Rio Grande suggesting that resistance to wilt was dominant. Generation mean analysis of six generations (P1, P2, F1, F2, BC1F1P1 and BC1F1P2) trials were conducted at two locations for two seasons in 2019. Significant location, generation differences and location x genotype interactions for all traits evaluated were detected across the four-cross combinations. The six generations of each of the four crosses performed better at Kabete...........................................................................