Diversity and heritability of tomato resistance to Ralstonia solanacearum

Abstract

Bacterial wilt (BW) incited by Ralstonia solanacearum, known to attack over 450 plant species in the tropics and subtropics, is a devastating disease limiting tomato production in Uganda and worldwide. This study aimed to determine the heritability of resistance to bacterial wilt in tomatoes and the genetic diversity of selected tomato genotypes. Two bacterial wilt-resistant (MT56 and BL333) and three susceptible commercially-desired (Assila, Rambo, and Heinz) tomato varieties were crossed in a North Carolina Design II in a screen house at Makerere University Agricultural Research Institute Kabanyolo to create a breeding population. The F1s were selfed and advanced to F2. Parents, F1s, and F2s were inoculated 18 days after planting, with Phylotype 3 (Ralstonia pseudosolanacearum) using the soil drench method and data collected on bacterial wilt intensity at 3-day intervals for 30 days after inoculation and analyzed for bacterial wilt reactions. At the same time, AVTO 1219 and AVTO 9802 were screened for resistance to bacterial wilt. The Area Under Disease Progress Curve was significant (F20,40 =3.14, p < 0.001), suggesting that cumulative disease progress was less in resistant genotypes of segregating generations. Disease severity increased with Days After Inoculation (DAI), with Heinz having the highest curve indicating the highest level of susceptibility to BW. In contrast, AVTO 1219 had the flattest curve showing the highest resistance level to the disease. Combining ability results indicated that the General Combining Ability for male parent (GCAm) was highly significant and Specific Combining Ability (SCAf×m) and GCAf were significant for the F2 generation at F2,10=7.56, p≤0.01. In both F1 and F2 generations, broad-sense heritability was higher than narrow-sense heritability, indicating that non-additive gene action predominantly controlled tomato resistance to bacterial wilt. The genetic diversity of 19 tomato genotypes was examined using fourteen SSR markers. The genetic diversity was between 0.5 and 0.6759, with a mean of 0.5787. The Polymorphism Information Content (PIC) ranged from 0.375 to 0.6357, with a mean of 0.4888, indicating a relatively high degree of diversity among these tomato genotypes. SLM 12-2 was the most polymorphic marker, with a PIC of 0.6357. Based on the cluster analysis using the Unweighted Pair-Group Method with Arithmetic Average (UPGMA), all the tomato genotypes fell into 6 clusters. The factorial component analysis (FCA) supported the clustering results. It is recommended that tomato breeding programs use AVTO 1219 and AVTO 9802.