Meiosis in sesquidiploid hybrids of Lycopersicon esculentum and Solanum lycopersicoides

Abstract

We have synthesized diploid hybrids between Lycopersicon escukntum 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.Thirty-five years have elapsed since the first report of successful hybridization between Lycopersicon esculentum (cultivated tomato) and Solanum lycopersicoides (wild nightshade endemic to southern Peru and northern Chile) (1). In the meanwhile intensive efforts in our laboratory and others have failed to yield progeny from selfing or sib-mating the highly sterile diploid hybrids thus generated or from backcrosses between them and L. esculentum. The parental species as well as the F1 hybrids have the same chromosome number (2n = 24). As indicated in the original report, doubling the chromosome number of the diploid hybrid results in a tetraploid with consistent bivalent chromosome pairing in meiosis and greatly improved fertility, hence a valid alloploid. Although breeding within such alloploids generates uniformly alloploid progeny, it has heretofore been impossible to backcross to diploid L. esculentum. It is the purpose of this article to report a breakthrough in this effort, yielding the expected sesquidiploid (allotriploid) hybrids by means of which transfer of desired genes from the wild parent to cultivated tomatoes may be possible.Research on chromosome pairing behavior in hybrids between these species has revealed much concerning the phylogenetic relationships of the parents. Thus, despite its extremely high sterility, the 2x F1 exhibits nearly complete pairing at meiotic pachytene (2, 3) and from a mean of 14.8 (1) to 20.2 (2) paired chromosomes at metaphase. Studies on the alloploid, on the other hand, reveal considerable differentiation between the two genomes, nearly all pairing taking place between parental homologues (4). The chromosomal pairing relations in the sesquidiploids having two sets of L. esculentum chro...

Unilateral incompatibility gene ui1.1 encodes an S-locus F-box protein expressed in pollen of Solanum species

“…Segregation for multiple pollen loci can be ruled out in allotetraploid SC × SI hybrids, because 100% of diploid pollen should express all necessary pollen factors from the SI parent. Allotetraploid S. lycopersicum × S. chilense and S. lycopersicum × S. lycopersicoides hybrids are also self-sterile (35,36). These observations imply that the S-haplotype of S. lycopersicum is incapable of overcoming SI through the competitive interaction mechanism in heteroallelic pollen.…”

Fine Mapping of ui6.1, a Gametophytic Factor Controlling Pollen-Side Unilateral Incompatibility in Interspecific Solanum Hybrids

“…edu). An allotriploid interspecific hybrid (GH266, Rick et al 1986), containing two genomes of S. lycopersicum (cv. UC82B) and one genome of S. lycopersicoides (LA1964), was used as a female tester line to detect pollen unilateral incompatibility factors (Figure 1, 'LLS').…”

Homeologous Recombination in Solanum lycopersicoides Introgression Lines of Cultivated Tomato

“…The L. esculentum and S. lycopersicoides 1 genomes are readily distinguished by genomic in situ hybridization and differ in the copy number and/or locations of certain repetitive DNA elements (Ji et al 2004). Differences were also found between them with respect to chromosome size and timing of condensation (Menzel 1962;Rick et al 1986). Allotetraploid hybrids show preferential pairing of homologous chromosomes, with complete bivalent formation and consequently greater fertility than 2x hybrids (Menzel 1964), suggesting that the genomes of S. lycopersicoides/S.…”