Somatic hybrids between Solanum melongena and S. sisymbrifolium, as a useful source of resistance against bacterial and fungal wilts

Abstract By using electrofusion of mesophyll protoplasts, 4 clones of somatic hybrids were produced between Solanum melongena cv. Pusa purple cluster and Solanum sisymbrifolium, a sexually incompatible wild relative resistant to bacterial ( Ralstonia solanacearum ) and fungal ( Verticillium dahliae ) wilts. All hybrids were morphologically homogeneous, normal and intermediate between the parents. They set flowers and produced fruits with empty seeds. Their hybrid status was confirmed by examining isoenzymes and random amplified polymorphism DNA analysis. Chloroplast-specific-cleaved amplified polymorphism sequence markers provided evidence that the 4 somatic hybrids possessed chloroplast genome from S. sisymbrifolium . Flow cytometry and chromosome countings revealed that all selected hybrids were tetraploids (2n=4x=48 chromosomes). The parental origin of the hybrid chromosomes was determined by using the techniques of genomic in situ hybridisation. Each hybrid contained one complete set of chromosomes from both parents. Neither spatial separation and recombinant chromosomes nor translocation could be demonstrated during mitotic metaphase. In vitro tests for resistance, using suspensions of two strains of R. solanacearum (race 1 and race 3) and the filtrate of culture medium of one strain of V. dahliae revealed that S. melongena was highly susceptible, whereas S. sisymbrifolium had variable levels of resistance. All somatic hybrids tested showed good levels of resistance, intermediate between those of the parents.