Isolation of Trisomics from Crosses of Diploid, Triploid, and Tetraploid Red Clover
The objectives of this study were to examine the fertility of crosses of various ploidies, to determine the chromosome numbers of progenies from these crosses, and to produce a complete series of primary trisomics in red clover. The ultimate goal is to use the primary trisomics for mapping of genes in this agriculturally important species. Seed set from 2x-3x, 3x-2x, 3x-3x, 3x-4x, and 4x-3x crosses of red clover (Trifolium pratense L.) averaged 9.4, 7.4, 6.3, 2.4 and 5.3% respectively. Chromosome numbers produced were 2n = 14, 15, 16, 21, 26 and 28. About one half of the progenies were diploid (2n 14), about one third trisomic (2n = 15), about 6% putative double trisomics (2n = 16), and about 4% had higher numbers. All classes of crosses, except those involving tetraploids, produced trisomics. The 3x-2x crosses produced higher percentages of trisomics, double trisomics and higher numbers than did 2x-3x crosses indicating greater female than male transmission of the extra chromosomes. Triploids used in these crosses contained either 21 or 22 chromosomes. The use of 21 chromosome triploids produced higher fertility than did 22 chromosome triploids. In 3x-2x crosses, 22 chromosome parents produced more double trisomics (15.9%) than did the 21 chromosome parents (6.1%). From a total of 37 trisomic plants, all seven of the possible primary trisomes of the red clover genome were tentatively isolated. Morphological differences were not associated with the different trisomics.
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