GENETIC DIVERSITY AND GEOGRAPHIC DIFFERENTIATION IN PAWPAW [ASIMINA-TRILOBA (L) DUNAL] POPULATIONS FROM 9 STATES AS REVEALED BY ALLOZYME ANALYSIS

As a new National Clonal Germplasm Repository for Asimina species at K entucky State University (KSU), of major concern to us is the genetic variation within our germplasm collection. The present study investiga ted the extent of genetic diversity for the pawpaw germplasm in our co llection and the geographical pattern of genetic diversity among popul ations using isozyme markers. Allozyme diversity was high in Asimina t riloba (L.) Dunal (Annonaceae) collected from all nine different state s, as is typical for temperate woody perennial, widespread and outcros sing plant species. Averaged across populations, mean number of allele s per locus (A), percent polymorphic loci (P), effective number of all eles per locus (A(c)), and expected heterozygosity (H-e) were 1.54, 43 .5, 1.209, and 0.172, respectively. Significant deviations from Hardy- Weinberg equilibrium were found in nine populations at an average of 4 .8 loci. Observed heterozygosity was higher than expected. Partitionin g of genetic diversity showed that 88.2% resided within populations. T he proportion of genetic diversity among populations (G(st) = 0.118; F -ST = 0.085) was either lower than or within the range of those specie s with similar ecological and life-history traits. The mean genetic id entity among populations was high (I = 0.988), An analysis using UPGMA clustered most populations as one major group, with the southernmost (Georgia) and the westernmost (Illinois) populations readily separated from the main group. The relationships discovered by principal compon ent analysis (PCA) were similar to those revealed by UPGMA, In additio n, PCA separated the northernmost population (New York) from the major group. Sampling strategies for future germplasm collection of A. tril oba are also discussed.