Meiosis in sesquidiploid hybrids of Lycopersicon esculentum and Solanum lycopersicoides.

We have synthesized diploid hybrids between Lycopersicon esculentum and Solanum lycopersicoides and have converted them to allotetraploids. Two sesquidiploids, having two complements of the former parent and one of the latter, have been obtained by backcrossing the former parent with the alloploid. In meiosis of the sesquidiploid the L. esculentum chromosomes exhibit strong preferential pairing, consistently forming 12 bivalents, whereas the S. lycopersicoides chromosomes remain unpaired. This chromosomal comportment conforms with expectations based on meiosis of the 2x and 4x hybrids. Condensation of the S. lycopersicoides univalents is retarded in early diakinesis but their development appears normal at later stages. Presumably as a consequence of the orderly behavior of the L. esculentum bivalents and consequent contribution to each gamete, fertility of the sesquidiploids is higher than in L. esculentum autotriploids. The normally strict self-incompatibility is somewhat relaxed in the sesquidiploids. Extra S. lycopersicoides chromosomes can be transmitted from the sesquidiploid as pistillate parent, and the aneuploid progeny are viable. Establishment of alien addition races and their utilization to transmit desired genes from S. lycopersicoides to L. esculentum are anticipated.