Phenotypic and genotypic screening for root-knot nematode (Meloidogyne incognita) resistance in tomato

Tomato ( Solanum lycopersicum L.) productivity is severely constrained by the root-knot nematode Meloidogyne incognita , which can reduce yields by 20–40% and, under heavy infestation, by more than 50%. To identify consistent sources of host resistance, 137 diverse tomato genotypes (exotic and indigenous cultivated lines, wild Solanum accessions, cherry types and released varieties) were evaluated under controlled artificial inoculation (2 J2 g –1 soil) across two contrasting seasons at ICAR-IARI, New Delhi. The inoculum, maintained as M. incognita race 1, was confirmed as M. incognita by perineal-pattern morphology and species-specific PCR. Phenotypic screening using the standardized root-knot gall index identified four Solanum peruvianum accessions (LA-1481, LA-1481-2, LA-2862 and LA-2802) that remained within the combined highly resistant/resistant group in both seasons, LA-1481 being highly resistant in both trials and LA-2862 shifting from resistant to highly resistant, whereas more than 70% of cultivated backgrounds were susceptible or highly susceptible, indicating a narrow resistance base. Pooled analysis of square-root-transformed gall counts under a completely randomized design showed a highly significant genotype effect, whereas neither the season effect nor the genotype × season interaction was significant. Of eighteen Mi -linked SCAR/CAPS primer pairs attempted, sixteen were scored across the panel and eight of these recorded resistance-associated calls, which were concentrated in the wild accessions but also occurred in a few cultivated lines; the Mi-3 -linked marker TG-263 showed the highest recorded concordance with the phenotypic classes (κ = 0.853), detecting resistance-associated alleles in LA-2862, LA-2802 and LA-1481. These accessions are promising donors, and the recorded marker profiles support their prioritisation, meriting confirmation through reproduction-based assays and multi-environment field evaluation.