Development of interspecific hybrids between Solanum lycopersicum L. and S. sisymbriifolium Lam. via embryo calli

Solanum sisymbriifolium, a wild relative of the S. lycopersicum species, has been found to be resistant to numerous pathogens which cause severe diseases in Solanaceae crops. It would be highly desirable for species strongly affected by diseases (e.g. tomato) to contain the resistant genes found in their wild relatives. Solanum sisymbriifolium has been considered of potential interest for S. melongena L. breeding, as the former is resistant to several pathogens and resistant interspecific hybrids have been obtained. Additionally, several reports indicate that S. sisymbriifolium is useful for tomato gynogenic haploid production. It is still not quite clear whether S. sisymbriifolium can be crossed with S. lycopersicum and the development of hybrid progeny is possible. In our preliminary in vivo crossing, S. lycopersicum × S. sisymbriifolium diploid embryos were formed inside fruits, but their development was inhibited at the globular stage. To obtain F1 hybrids the embryo-rescue method was implemented. Globular embryos isolated 14–35 dap were cultured on various media showing varied morphogenic potencies. Most of the embryos did not develop on the used media but calli formed from the embryogenic cells in > 17% of the embryos, allowing hybrid plants to be obtained. Ten regenerants, which were adapted in pots containing soil, had morphological traits similar to the S. sisymbriifolium parent, including the plant habit, presence of prickles on shoots or white colour of flowers. The hybrid origin of the regenerants was confirmed by flow cytometry analysis of DNA content and KASP genotyping. The results indicated that S. lycopersicum can be hybridized with S. sisymbriifolium through interspecific hybridization to introduce novel traits for use in tomato-breeding programmes.