5S Nuclear Ribosomal Gene Variation in the Glycine tomentella Polyploid Complex (Leguminosae)

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Abstract
Glycine tomentella, a perennial wild relative of the soybean, is a species complex consisting of several reproductively isolated diploid (2n = 38, 40) and polyploid (2n = 78, 80) races. Variation in the repeat lengths of the nuclear multigene family encoding 5S ribosomal RNA was assayed for 20 diploid and 30 polyploid accessions from Australia, Papua New Guinea, Philippines, and Taiwan. These accessions represent all of the reproductively isolated and isozymically differentiated groups known to occur in the complex, including the recently described segregate, G. arenaria. Diploid G. tomentella accessions were found to have one of three size classes of 5S repeat, with good correlation between size class and isozyme group; G. arenaria possessed a repeat different in length from all G. tomentella accessions. Of the six classes of polyploids known from the complex, four had two major size classes of 5S repeats in each individual, three of them combining sizes found in the diploids. Two other polyploid isozyme races had only a single major repeat class. Hypothetical parents for hybrid origins of polyploids are suggested, and the consistency of these hypotheses with previously published evidence from isozyme and hybrid meiotic analysis is discussed.

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