Allozyme polymorphisms within and among local varieties of maize
in Southwestern China
--H. Lu, Y. L. Zheng, J. S. Li, X. Z. Xiong and J. L. Liu
There is abundant germplasm of maize in China, and more than 8000 local varieties have been collected in 1984. Although local varieties have provided much of the germplasm currently available to maize genetics and breeders in China, they have been little evaluated for their genetic variability.
In this paper, genetic polymorphisms on 18 isozyme loci were investigated for 27 local varieties in Southwestern China. The number of seedlings assayed per variety ranged from 35 to 105. A random sample of seedlings from each variety was assayed by horizontal starch (Sigma Co.) gel electrophoresis. One sample of each of inbred lines Mo17 and Oh43 was taken as a standard on each gel to aid gel reading. The methods described by Stuber (North Carolina Univ. Techn. Bull. 286, 1988) were employed for electrophoresis and denoting alleles for each locus.
Table 1. Allele numbers detected at isozyme loci in different maize
Allele numbers on each locus are listed in Table 1. In order to compare with other studies, Table 1 also includes allele numbers detected in 72 U.S. important inbred lines (Smith et al., 1985), 12 U.S. Corn Belt open-pollinated populations (Kahler et al., 1986) and 31 races of maize in Bolivia (Goodman and Stuber, 1983). It was shown that at most loci, the number of alleles observed per locus in 27 local varieties was more comparable to the number of alleles observed in 72 U.S. important inbred lines and 12 Corn Belt open-pollinated populations, but less than the number of alleles observed in 31 races of maize in Bolivia. The results indicated that there were extensive allozyme polymorphisms and abundant genetic variability in local varieties in Southwestern China, and that those local varieties were valuable germplasm.
Gene diversity was analysed by Nei's methods (Molec. Pop. Genet. Eval., Elsevier Publ, 1975). The gene diversity in the total population (Ht) can be divided into the gene diversities within and between subpopulations (varieties), signified by Hs and Dst (Dst = Ht-Hs), respectively. The relative and absolute magnitude of gene differentiation among varieties may be measured by Gst (Gst = Dst/Ht) and Dm, respectively. Analysis of gene diversity in 27 local varieties is presented in Table 2. acp4 had the maximum gene diversity in total population (0.650), followed by acp1, mdh1, mdh3 and cat3, at which there were extensive allozyme polymorphisms. The minimum Ht was 0.0042 at locus mmm, and Ht's at loci of mdh5, got3 and phi1 were less than 0.100, indicating that those loci were stable and had few allozyme polymorphisms. Gst ranged from 0.003 (mdh5) to 0.497 (pgd2) below 0.500, indicating that gene diversity at a single locus is mainly contained within varieties. Average Gst calculated from 18 isozyme loci was 0.289, and revealed 71.1% and 28.9% of gene diversity contained within and among varieties, respectively. Average Dm from 18 loci was 0.088, meaning that an estimate of the net gene codon differences between varieties and independent of the gene diversity within varieties was 0.088, higher than in most other organisms.
Table 2. Gene diversity at 18 isozyme loci of 27 local varieties of
maize in Southwestern China.
The results of the electrophoretic assays showed that extensive allozyme polymorphism was the predominant feature of the 27 local varieties. The gene diversity in the total population mainly occurred within varieties rather than among them.
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