Sexual hybridization of Lycopersicon esculentum and Solanum rickii by means of a sesquidiploid bridging hybrid.

A sesquidiploid hybrid having two genomes of Lycopersicon esculentum and one of Solanum lycopersicoides served as a pistillate bridging parent in crosses with Solanum rickii to produce L. esculentum x S. rickii hybrid progeny. Of the four progeny obtained, one (GH2754) was diploid and three were aneuploid with extra S. lycopersicoides chromosomes. The hybrids had morphological features of both parents, but attributes of the wild parent dominated. The hybrid nature of the four progeny was confirmed by isozyme, restriction fragment length polymorphism, and cytological analyses. A mean of 9.15 bivalents was observed in pollen mother cells of GH2754. A high level of pollen abortion was seen in all hybrids. Crosses of the hybrids with staminate S. rickii yielded one backcross individual, revealing a very low, but certain level of female fertility. Colchicine treatment of GH2754 generated one promising amphidiploid hybrid, which exhibited strong preferential chromosome pairing (94% of the examined cells had 24 bivalents) and appreciable pollen fertility (43% stainable). Chromosome pairing, isozyme, and restriction fragment length polymorphism data support a very close relationship between the two Solanum spp. and a much greater distance between them and L. esculentum, but the data do not discriminate between them in respect to their distances from the latter. The cytological and molecular observations, previous reports of successful transfer of traits from S. lycopersicoides to L. esculentum, and our hybridization of L. esculentum x S. rickii suggest good prospects for gene transfer from S. rickii to L. esculentum.