Development of interspecific hybrids through embryo rescue for heat-stable nematode resistance ( Mi-9 gene) from Solanum arcanum in tomato

Tomato ( Solanum lycopersicum L.) is the most important vegetable crop grown in India after potato. Root-knot nematodes (RKNs) ( Meloidogyne spp.) cause yield loss between 11 and 35% in tomato. RKNs are also known to be involved in the tomato wilt disease complex in association with Fusarium oxysporum sp. lycopersici and Ralstonia solanacearum . The nematode resistance gene, Mi1 from Solanum peruvianum, is currently the only source of RKN resistance in modern tomato cultivars. Mi1 mediated resistance is temperature sensitive and ineffective above 28 °C soil temperature. Nematode resistance gene, Mi-9 found in S. arcanum accession LA2157 is heat-stable and is located on the short arm of chromosome 6. In our study, LA2157 was crossed with tomato cultivar Kashi Amrit. The inter-specific hybrid was successfully developed through embryo rescue. The hybridity of embryo rescued plants was confirmed by morphological features and molecular marker assay. LA2157 and F 1 hybrid showed immune reaction to M. incognita under the high inoculation pressure of 2000s stage infective juveniles per plant, while cv. Kashi Amrit exhibited a highly susceptible reaction. Among hundred F 3 plants from ten F 2 s, ten F 3 plants each of two separate F 3 families (43 and 119) have shown resistance and no segregation was observed within the family for resistance during April–May, 2020 (high temperature). All F 4 plants derived from 43F 3 also gave an immune reaction to M. incognita indicating homozygous nature of 43F 2 plant for Mi-9 gene. We believe that this set of resistant plants can be utilized to transfer heat-stable nematode resistance in the background of cultivated tomatoes.