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Interspecific crossability and cytogenetic analysis of sexual progenies of Mexican wild diploid 1EBN species Solanum pinnatisectum and S. cardiophyllum

Chen, Q., Lynch, D., Platt, H.W., Li, H.Y., Shi, Y., Li, H.J., Beasley, D., Rakosy-Tican, L., Theme, R.
American journal of potato research 2004 v.81 no.2 pp. 159-169
Leptinotarsa decemlineata, Phytophthora infestans, Solanum pinnatisectum, chromosome pairing, chromosomes, cytogenetic analysis, diploidy, economics, embryogenesis, endosperm, genes, genotype, germplasm, hybrids, insects, interspecific hybridization, metaphase, pollen, potatoes
Mexican wild diploid species, Solarium pinnatisectum (S. pnt) (2n=2x=24, 1EBN: endosperm balance number) is a useful germplasm source of late blight and Colorado potato beetle (CPB) resistance in potato improvement. However, it is very difficult to cross this species with other 1EBN Solarium species. Sexual hybrids among three accessions of S. pnt and two accessions of S. cardiophyllum (S. cph) (2n=2x=24,1EBN) were studied. There were large differences in the cross-compatibility among the genotypes and accessions from these two 2x-1EBN species. Interspecific incompatibility existed in the crosses between S. pnt and S. cph, in which S. cph functioned only as the male parent. The crosses with accessions PI 275236 of S. pnt produced 35 hybrids following the conventional propagation procedures. Seven hybrids were obtained with the S. pnt accession PI 275233 with the aid of embryo rescue, while hybridization involving accession PI 253214 resulted in no fruit. The cytogenetic analysis indicated that all of the hybrids derived from crosses of accession PI 275233 of S. pnt with S. cph had 2n = 24 chromosomes and were pollen fertile. Crosses involving accession PI 275236 of S. pnt produced both 2x (2n=24) and 3x (2n=36) hybrids. Meiotic analysis at metaphase I of pollen mother cells (PMCs) showed a fairly high rate of chromosome pairing that averaged between 10.10 and 11.10 bivalents per cell in most of the 2x hybrids, indicating S. pnt and S. cph have the similar genome. A high frequency of trivalents and quadrivalents were observed in 3x hybrids derived from S. pnt 2 x S. cph 1, indicating homology exists among these chromosomes. These results suggest that specific gene(s) and not either differences between genomes or EBN controlled interspecific crossability and embryo development. The disease and insect tests on the 2x and 3x hybrids revealed that all have high levels of resistance to both late blight and CPB. Thus it could appear that selection of genotypes is a key for successful interspecific hybridization when using Mexican wild diploid species as a source of economic important traits.