Genetic Diversity Of Pepper (Capsicum Annuum L.) Germplasm Revealed By RAPD Markers

Pepper (Capsicum annuum L.) is a popular vegetable in many countries. It was introduced to China more than 400 year ago. But the classification of pepper is still a controversial question. In Capsicum, many breeding programs involve intraspecific crosses between varieties. So the study of genetic diversity among C. annuum varieties is very important to the breeding programs. RAPD (random amplified polymorphyic DNA) is simple, cost-efficient, and fast technique. It has been used extensively in search of polymorphism in plants. We report here polymorphisms and genetic relationship of 34 pepper cultivars planted in China by RAPD technique.For every cultivar, genome DNA was isolated from fresh leaves of ten plants using CTAB method. DNA sample extracted by this method was of good quality. The CTAB method was simple and efficient and was suitable for a large number of RAPD analyses.Twenty-two 10 bp primers, which could amplify stable and polymorphic RAPD bands, were selected for the RAPD analysis. The 22 primers amplified 123 bands totally among 34 pepper cultivars with an average of 5.6 bands per primer. And of these 123 bands 68 (55.3%) were polymorphic in the 34 cultivars with an average of 3.1 bands per primer.Genetic distances were calculated using three different methods, Nei's method. Jaccard's method, and Euclidean distance method. Three tree diagrams were constructed based on three genetic distance matrixes respectively using UPGMA (unweighted pair group method using arithmetic average) cluster analysis. It was showed on the dendrograms that cultivars belonging to the same variety according to Bailey's classification system clustered together. But it was also showed that the genetic distance between var. cerasiforme and var. fasciculatum was much shorter than others, therefore it was more reasonable to treat these two varieties as one rather thantwo individual varieties, which was in accord with IBPGR's classification. The relationships among the five varieties based on Nei's and Jaccard's methods were the same, but Euclidean distance method gave different result. In previous studies, there were two opinions. Some researchers considered that varieties of the pungent type had a more remote relationship with the sweet type. But some others considered that some pungent cultivars had a nearer relationship with sweet type than with the other pungent types. In our study, according to Nei's and Jaccard's methods, var. conoides, a pungent type, had a nearer relationship to var. grossum the sweet type, which was in accord with the latter.Var. longum and var. grossum were more divergent than the others, which was in accord with the fact of their wider cultivation. Different germplasm introduced through breeding programs might cause the variety more diverse. Cultivation played an important role in the development of pepper varieties. While the influence of geography was not so significant as expected.Although there was no primer that could identify all the 34 individual cultivars, 27 cultivars could be identified by one primer individually. It is possible that the RAPD fingerprint could be employed to identify each pepper cultivar.