Estimate of General and Specific Combination Ability in Tomato for Production of Hybrids Resistant to Bacterial Wilt

To estimate the combining ability, two groups of tomato genotypes for the production of resistant hybrids to bacterial wilt were evaluated. The experiments were carried out in phyto bacteriology laboratory and in greenhouse facility of the department of agronomy at Federal Rural University of Pernambuco, between June and September 2016. A parental group with wilt resistant cultivars Yoshimatsu and Hawaii 7996 as testers and the second group consisted of 10 lines and the two susceptible cultivars IPA-6 and Santa Clara. The diallel analysis was according to the method of Geraldi and Miranda Filho, type G2, employed in estimating the general (GCA) and specific (SCA) combining ability and other genetic parameters. The crosses that showed the highest performance for resistance were the hybrids of Yoshimatsu with the line L04 and Hawaii 7996 with the L125, because they were observed with a positive SCA for the period of latency (LP-50) and negative for the other characters studied. It was observed that additive effects were involved for bacterial wilt index (BWI), incidence (INC) and area under the disease progress curve (AUDPC) and non-additive effects were involved for all the four resistance components (BWI, INC, LP-50 and AUDPC) studied. The genetic parameters of BWI and LP-50 for the isolate CRM 74 and AUDPC for the isolates CRM 74 and CRM 77 had coefficients of genotype variation above the coefficient of environmental variation, with a CVg/CVe above 1.0 and a high genetic variance. The highest heritability was in AUDPC for both isolates with 88.24% and 75.90% respectively. The L125 line presented greater GCA to main resistance components for the main resistance components for CRM 74 and CRM77 isolated. The hybrid Yoshimatsu x L04 combination stood out with a higher SCA.