| The cultivated peanut or groundnut (Arachis hypogaea L.) is an important crop used for its oil and protein source worldwide. Because of the lack of polymorphism at DNA level, this crop has lagged behind in genetic mapping, marker-assisted selection, resistance gene cloning, and crop evolutionary study compared with other crops. This problem has hindered the improvement of cultivated peanut by molecular techniques. The study involved a selection of 116 groundnut genotypes, comprising 97 germplasm accessions of A.hypogaea L. originating from 9 countries, and 19 wild species of genus Arachis. The objectives of this study were to assess genetic variation using RAPD, SSR and AFLP molecular markers in genus Arachis and to classify the tested peanut germplasm at molecular level by cluster analysis. Results show that the RAPD technique with low informativeness and low reproducibility in tested peanut germplasm was abandoned for scoring in the present study, and that the SSR technique had the most abundant informativeness and the highest reproducibility among the three DNA fingerprinting techniques. Average SSR marker genetic diversity among the 24 peanut germplasm of vax.fastigiata was 0.59 and ranged from 0.08 to 0.84, which was detected with 16 polymorphic primer pairs. Average SSR marker genetic diversity among the 24 peanut germplasm of var.hypogaea was 0.46 and ranged from 0.05 to 0.74, which was detected with 15 polymorphic primer pairs. The SSR marker genetic distance ranged from 0.04 to 0.69, with an average of 0.37 among the 24 genotypes of var.vulgaris Harz, which was detected with 10 polymorphic primer pairs. The SSR marker genetic distance ranged from 0.03 to 0.33, with an average of 0.17 among the 24 accessions of yat.hirsu.ta Kohler, which was detected by 13 polymorphic primer pairs. The greatest genetic diversity was between the species of genus Arachis, the SSR marker genetic distance ranged from 0.33 to 0.91, with an average of 0.76 among the 24 accessions detected with 21 polymorphic primer pairs. Up to 15 polymorphic primer combinations were needed to distinguish the 24 peanut germplasm of A.hypogaea L., and average AFLP marker genetic diversity was 0.12 and ranged from 0.01 to 0.36. In a set of 38 peanut germplasm, comprising of 24 acccessions from different botanical varieties of A.hypogaea L. and 14 wild germplasm from six sections of genus Arachis, the SSR marker genetic distance ranged from 0.00 to 1.00, with an average of 0.65, which was detected by 7 SSR primer pairs, and the average AFLP genetic distance was 0.42, and ranged from 0.01 to 0.79 in the same set of genotypes detected with the 15 AFLP primer combinations.Six conclusions emerge from the results provided by the present study. First, the presence of abundant polymorphic SSRs in peanut germplasm belonging to one of the four botanical varieties, respectively, demonstrates that this type of genetic maker is useful tools for molecular map development, genotype identification, genetic enhancement, germplasm management, and other uses. The highly polymorphic nature of SSR markers make them particularly advantageous in a species such as peanut in which RFLP,RAPD and AFLP has been somewhat difficult to detect, and more SSR markers need to be developed. Second, each botanical variety of A.hypogaea L. can be further divided into sub-cluster in terms of molecular genetic distance. Third, the molecular classification based on SSRand AFLP marker genetic distance in peanut germplasm of A.hypogaea L. is in general agreement with the classification system according to agronomic and botanical traits by Sun Da-rong (1956) or Krapovickas (1968).On the other hand, it is valid that Krapovickas and Gregory (1994) divided the A.hypogaea L. into six botanical varieties in terms of DNA polymorphism in the cultivated peanut reported in the present study. Fourth, it was first reported that the wild species A.spegazzinii is one of the ancestor of A.hypogaea L. based on SSR and AFLP markers. Fifth, the phylogenetic relationships among four botanical varieties... |
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