Nematode Resistance Mechanisms in Wild Solanum Species and Their Translational Value for Improving Tomato Production in Nigeria’s Irrigated Zones

Root-knot nematodes (Meloidogyne spp.), particularly M. incognita, M. javanica, and M. arenaria, cause severe losses in irrigated tomato production across Nigeria's North West and North Central zones, and the durability of the Mi-1.2 gene deployed in commercial resistant varieties is threatened by emerging virulent populations. Wild Solanum species represent a largely untapped reservoir of alternative nematode resistance mechanisms, including novel resistance genes, physical barriers, and biochemical defences. This doctoral research systematically characterises nematode resistance mechanisms in eight wild Solanum species, including S. torvum, S. sisymbriifolium, S. peruvianum, S. habrochaites, and four endemic African Solanum species, through morphological, physiological, biochemical, and molecular investigation. The research design includes: controlled inoculation assays with five Nigerian Meloidogyne isolates representing the three major species; microscopic characterisation of hypersensitive response, cell wall reinforcement, and nematode penetration and development inhibition; proteomic profiling of resistant and susceptible interactions at 24 and 72 hours post-inoculation; and QTL mapping in an interspecific cross between S. torvum and susceptible tomato using a 150-member population. The research generates the first QTL map for S. torvum nematode resistance using markers relevant to tomato breeding programmes active in Nigeria. An original theoretical contribution is a multi-mechanism resistance model integrating physical, biochemical, and molecular components of wild Solanum nematode resistance applicable to crop improvement in tropical irrigated systems. Keywords: root-knot nematodes, Solanum, resistance mechanisms, QTL mapping, Nigeria.