QUALITATIVE AND QUANTITATIVE CHARACTERIZATION OF RAPD VARIATION AMONGSNAP BEAN (PHASEOLUS-VULGARIS) GENOTYPES

Ten snap bean (Phaseolus vulgaris) genotypes were screened for polymor phism with 400 RAPD (random amplified polymorphic DNA) primers. Polymo rphic RAPDs were scored and classified into three categories based on ethidium bromide staining intensity. An average of 5.19 RAPD bands wer e scored per primer for the 364 primers that gave scorable amplificati on products. An average of 2.15 polymorphic RAPDs were detected per pr imer. The results show that primer screening may reduce the number of RAPD reactions required for the analysis of genetic relationships amon g snap-bean genotypes by over 60%. Based on the analysis of the distri bution of RAPD amplification, the same number of polymorphic RAPDs wer e amplified from different genotypes for all RAPD band intensity level s. A comparison of RAPD band amplification frequency among genotypes f or the three categories of bands classified by amplification strength revealed a measurable difference in the frequencies of RAPDs classifie d as faint (weakly amplifying) compared to RAPD bands classified as bo ld (strongly amplifying) indicating a possible scoring error due to th e underscoring of faint bands. Correlation analysis showed that RAPD b ands amplified by the same primer are not more closely correlated then RAPD bands amplified by different primers but are more highly correla ted then expected by chance. Pairwise comparisons of RAPD bands indica te that the distribution of RAPD amplification among genotypes will be a useful criterion for establishing RAPD band identity. For the avera ge pairwise comparison of genotypes, 50% of primers tested and 15.8 % of all scored RAPDs detected polymorphism. Based on RAPD data Nei's av erage gene diversity at a locus was 0.158 based on all scorable RAPD b ands and 0.388 if only polymorphic RAPD loci were considered. RAPD-der ived relationships among genotypes are reported for the ten genotypes included in this study. The data presented here demonstrate that many informative, polymorphic RAPDs can be found among snap bean cultivars. These RAPDs may be useful for the unique identification of bean varie ties, the organization of bean germplasm, and applications of molecula r markers to bean breeding.