LOCALIZATION OF THE LE2 LOCUS OF COTTON (GOSSYPIUM-HIRSUTUM L)
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Hybrid lethality systems are widely distributed among angiosperms and are of biological, evolutionary, and genetic interest, as well as being of potential importance for genetic manipulations. The Le2dav allele occurs naturally in the two Gossypium D3-genome species, G. davidsonii and G. klotzschianum, isolating them from other species of the cotton genus that carry A or D genomes. Le2dmv was previously transferred to G. hirsutum and found to be allelic to the Le2 locus of chromosome 26. Le2dmv was shown to interact differentially with its allele Le2 and its paralogous allele in chromosome 12, Le,. In this study, monotelodisomic tests were made to locate the Le2 locus to an arm of chromosome 26. A potentially hemizygous Le1Le1Le2(Le2) plant monotelodisomic for the short arm of chromosome 26 (Te26sh) was crossed with le1le1Le2davLe2dev Euploid F1S1 progenies from euploid (Le, Lef, Le2,e2) and Te26sh (Le, le, (LeJ, le2) F, plants were testcrossed with le, leJ Le, lai 'Le2da1', and the resulting FtSjTC families were scored to determine genotypes of respective F1S1 parents. Segregation among the F^TC families indicated that the Le2 locus is located in the long arm of chromosome 26, or within 5 cM of the centromere in the short arm. The data also revealed that the LerLe2dav interaction caused necrosis more quickly than did the Le2-Le2dav interaction. Individual F^TC plant segregations fit poorly with Mendelian expectations. Estimates of differential emergence for F^TC seed genotypes were used to amend raw data in an unbiased manner, resulting in better fits to expected segregation ratios and increased homogeneity among families. The results lend credence to previous inferences that differential viability can cause non-Mendelian ratios among individual plants segregating for alleles of this hybrid lethality system, and also indicate that it should be possible to use Te26sh stocks to develop isolines differing at the Le2 locus. Such stocks would facilitate comparisons of Le2 alleles from different sources and thus the analysis of polymorphisms of the Le2 locus, which might further our understanding of how hybrid lethality and sublethality systems evolve and contribute to speciation. 1990 The American Genetic Association.
