Restriction fragment length polymorphism analysis of somatic hybrids between Lycopersicon esculentum and irradiated L. peruvianum: evidence for limited donor genome elimination and extensive chromosome rearrangements.

The genome composition of asymmetric somatic hybrids, obtained by fusion of leaf protoplasts from Lycopersicon esculentum and gamma-irradiated leaf protoplasts from L. peruvianum, was characterised by Southern blot analysis using 29 restriction fragment length polymorphism markers. Eight "low dose hybrids" and seven "high dose hybrids" (irradiation dose 50 Gray and 300 Gray, respectively) were analysed. By densitometric scanning of the autoradiographs, the number of alleles for each locus of the component species was established. In general, elimination of alleles from the irradiated L. peruvianum donor genome was limited and ranged from 17%-69%. Three L. peruvianum loci, located on chromosomes 2, 4 and 7, were present in all asymmetric hybrids, suggesting linkage to the regeneration capacity trait which was used in selecting them. The loss of donor genome was dose-dependent. Low dose hybrids contained more alleles, loci and complete chromosomes from L. peruvianum than high dose hybrids, whereas the high dose hybrids contained more incomplete chromosomes. In most hybrids some L. esculentum alleles were lost. The possible implications of these results for the use of asymmetric hybrids in plant breeding are discussed.