USING ISOZYME POLYMORPHISMS FOR IDENTIFYING AND ASSESSING GENETIC-VARIATION IN CULTIVATED PAWPAW [ASIMINA-TRILOBA (L) DUNAL]

The utility of isozyme phenotypes for identifying and determining gene tic variation in pawpaw cultivars was studied using isoelectric focusi ng in thin-layer polyacrylamide gels. Based on a sample of 32 clones ( cultivars and advanced selections) and 23 enzyme systems, 7 enzymes we re found to be polymorphic, involving 9 polymorphic loci [acid phospha tase (ACP), dihydrolipoamide dehydrogenase (DDH), malic enzyme (ME), p hosphoglucoisomerase (PGI), phosphoglucomutase (PGM), peroxidase (PRX) , and shikimate dehydrogenase (SKD)]. Altogether these 9 loci and 32 c lones yielded 28 multi-locus isozymic phenotypes useful for cultivar i dentification; 24 of the 32 clones were uniquely identified. The alloz yme variation in these clones has the average of other long-lived wood perennials of widespread geographic range in temperature regions with insect-pollinated outcrossing breeding systems, secondary asexual rep roduction, and animal-dispersed seed. Genetic differentiation among th ese pawpaw clones, measured by Nei's distance, D, was substantial: 496 pairwise comparisons of genetic distance among the 32 clones indicate d that they differed on average of D = 0.068 +/- 0.04 and ranged from 0 to 0.188. Cluster analysis (UPGMA) produced a most likely division o f the 32 clones in 7 groups; however, these groups did not conform to pedigree relations. Additional polymorphic enzymes are needed for accu rate allozyme-based genetic discrimination.