Gametic Selection at Fatty Acid and Allozyme Marker Loci and Meiosis within Cuphea viscosissima × Cuphea lanceolata Populations
- T. Brandt and
- S. J. Knapp
The seed oils of many of the 260 species of Cuphea (Lythraceae) are rich natural sources of medium-chain fatty acids. Among them are C. viscosissima Jacq. (2n = 2x = 12) and C. lanceolate Ait. (2n = 2x = 12). These species show promise as oilseed crops and, as a consequence, are being domesticated. Hybrids were made between C. viscosissima (VS) and C. lanceolata f. silenoides (LNS) and between C. viscosissima and C. lanceolata f. typica (LNT) to assess their usefulness for breeding Cuphea. Microsporocytes of VS, LNS, LNT, and their hybrids were observed at metaphase I and anaphase I. Allozyme and fatty acid synthesis (FAS) marker loci were assayed within VS × LNS F2 and backcross populations to test for gamete and heterozygote selection. The cross VS × LNS was female- and male-fertile, whereas VS × LNT was female- and male-sterile. Bivalent pairing and regular chromosome segregation was observed for 94.0 and 0.0% of the microsporocytes from VS × LNS and VS × LNT, respectively. Mean chiasma frequencies within VS × LNS and VS × LNT were 0.53 and 0.26, respectively. Genome and arm affinity index estimates for VS × LNS were 0.98 and 0.65, respectively. Genome and arm affinity index estimates for VS × LNT were 0.52 and 0.34, respectively. Wildtype caprylic and capric acid percentage differences of VS and LNS were explained by an incompletely dominant natural mutation at the cap-1 locus—two and three nonoverlapping phenotypic distributions were observed for caprylic acid percentage within backcross or F2 populations, respectively. Thirteen of 20 marker segregation ratios and 12 of 18 allele frequency ratios were distorted—LNS alleles were overabundant more often than VS alleles. The was an overall excess of LNS alleles of 7.9%. The VS × LNS populations are useful for breeding—they undergo bivalent pairing and normal chromosome segregation—while meiosis is abnormal within VS × LNT populations.
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