Allelic variation at (TAA)n microsatellite loci in a world collection of chickpea (Cicer arietinum L.) germplasm |
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Authors: | Udupa S M Robertson L D Weigand F Baum M Kahl G |
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Institution: | (1) International Center for Agricultural Research in the Dry Areas (ICARDA) P.O. Box 5466, Aleppo, Syria e-mail: S.Udupa@cgiar.org; Fax: +963-21-2213490,;(2) Plant Molecular Biology Group, Biocenter University of Frankfurt, Marie-Curie Strasse 9 D-60439 Frankfurt/Main, Germany, DE |
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Abstract: | A set of 12 randomly selected (TAA)n microsatellite loci of the cultivated chickpea (Cicer arietinum L.) were screened in a worldwide sample comprising 72 landraces, four improved cultivars and two wild species of the primary
gene pool (C. reticulatum and C. echinosperum) to determine the level and pattern of polymorphism in these populations. A single fragment was amplified from all the accessions
with each of 12 sequence-tagged microsatellite site markers, except for one locus where no fragment was obtained from either
of the two wild species. There was a high degree of intraspecific polymorphism at these microsatellite loci, although isozymes,
conventional RFLPs and RAPDs show very little or no polymorphism. Overall, the repeat number at a locus (excluding null alleles)
ranged from 7 to 42. The average number of alleles per locus was 14.1 and the average genetic diversity was 0.86. Based on
the estimates obtained, 11 out of the 12 frequency distributions of alleles at the loci tested can be considered to be non-normal.
A significant positive correlation between the average number of repeats (size of the locus) and the amount of variation was
observed, indicating that replication slippage may be the molecular mechanism involved in generation of variability at the
loci. A comparison between the infinite allele and stepwise mutation models revealed that for 11 out of the 12 loci the number
of alleles observed fell in between the values predicted by the two models. Phylogenetic analysis of microsatellite polymorphism
in C. arietinum showed no relationship between accession and geographic origin, which is compatible with the recent expansion of this crop
throughout the world.
Received: 18 September 1998 / Accepted: 2 December 1998 |
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Keywords: | Microsatellite polymorphism Mutation mechanisms Replication slippage Infinite allele model Stepwise mutation model |
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