RAPD Inheritance and Diversity in Pawpaw (Asimina triloba)

ADDITIONAL INDEX WORDS. Annonaceae, dominant inheritance, allele frequency, Nei's genetic identity and distance, cluster analysis ABSTRACT. Twelve, 10-base primers amplified a total of 20 intense and easily scorable polymorphic bands in an interspecific cross of PPF1-5 pawpaw (Asimina triloba (L.) Dunal. ) x RET (Asimina reticulata Shuttlew.). In this cross, all bands scored were present in, and inherited from, the A. triloba parent PPF1-5. Nineteen of the 20 bands were found to segregate as expected (1:1 or 3:1) based on chi-square goodness-of-fit tests, and were subsequently used to evaluate genetic diversity in populations of A. triloba collected from six states (Georgia, Illinois, Indiana, Maryland, New York, and West Virginia) within its natural range. Analysis of genetic diversity of the populations revealed that the mean number of alleles per locus was A = 1.64, percent polymorphic loci was P = 64, and expected heterozygosity was He = 0.25. No significant differences were found among populations for any of the polymorphic indices. Partitioning of the population genetic diversity showed that the average genetic diversity within populations was Hs = 0.26, accounting for 72% of the total genetic diversity. Genetic diversity among populations was Dst = 0.10, accounting for 28% of the total genetic diversity. Nei's genetic identity and distance showed a high mean identity of 0.86 between populations. Genetic relationships among the populations examined by unweighted pair-group mean clustering analysis separated the six populations into two primary clusters: one composed of Georgia, Maryland, and New York, and the other composed of Illinois, Indiana, and West Virginia. The Georgia and Indiana populations were further separated from the other populations within each group. This study provides additional evidence that marginal populations within the natural range of A. triloba should be included in future collection efforts to capture most of the rare and local alleles responsible for this differentiation. The genus Asimina Adans. is the only temperate representa- tive of the tropical Annonaceae, the largest primitive family of flowering plants, containing ≈130 genera and 2000 species (Cronquist, 1981). The genus Asimina includes nine species, which are indigenous to the United States (Kral, 1960). The best- known species is Asimina triloba, the North American pawpaw, which is the largest tree fruit native to the United States. Pawpaw fruit have an oblong shape with green skin and a taste that can be described as a very sweet blend of banana ( Musa ×paradisiaca L.), mango (Mangifera indica L.), and pineapple (Ananas comosus (L.) Merr. ) flavors with a mild pleasant fruit aroma. Its fruit quality, nutritional value, natural defense compounds (annonaceous acetogenins) and landscaping appeal, make paw- paw of great potential for commercial development as a new alternative fruit tree crop and ornamental in the United States and elsewhere (Johnson et al., 1996; Jones and Layne, 1997; Layne, 1996). The natural range of A. triloba covers most of eastern North America, ranging from northern Florida to southern Ontario,