Relationship between root diameter and resistance of tropical chilli pepper genotypes to Ralstonia pseudosolanacearum

Ralstonia pseudosolanacearum is an important plant pathogenic bacterium that causes wilt disease in pepper plants. To manage this disease, one approach is to breed cultivars that are resistant to bacterial wilt through resistance development. The objective of this study is to investigate the potential correlation between the root xylem vessel diameter (XD) and resistance to R. pseudosolanacearum bacterial wilt in 50 tropical chili pepper genotypes. The experiment was performed by inoculating chili pepper seedlings with a mixture of nine isolates of R. pseudosolanacearum and using an alpha design with four replications. Furthermore, the seedlings of each genotype were sampled for the observation of XD. The results showed that 5, 4, 11, and 30 of the 50 genotypes were resistant, moderately resistant, moderately susceptible, and susceptible. Genotype resistance was unaffected by root morphology but was affected by XD. Meanwhile, significant relationships (P < 0.001) were found between XD and disease incidence, disease severity, and area under the disease progress curve. The XD of resistant and susceptible genotypes ranged from 201.70 µm to 469.33 µm and 25.62 µm to 97.25 µm, respectively. It was suggested as a marker phenotype for resistance to R. pseudosolanacearum, which was higher in genotypes with thick root xylem.