Genetic Diversity and Geographic Differentiation in Pawpaw [Asimina triloba (L.) Dunal] Populations from Nine States as Revealed by Allozyme Analysis

Abstract

<jats:p>As a new National Clonal Germplasm Repository for <jats:italic>Asimina</jats:italic> species at Kentucky State University (KSU), of major concern to us is the genetic variation within our germplasm collection. The present study investigated the extent of genetic diversity for the pawpaw germplasm in our collection and the geographical pattern of genetic diversity among populations using isozyme markers. Allozyme diversity was high in <jats:italic>Asimina triloba</jats:italic> (L.) Dunal (Annonaceae) collected from all nine different states, as is typical for temperate woody perennial, widespread and outcrossing plant species. Averaged across populations, mean number of alleles per locus (A), percent polymorphic loci (P), effective number of alleles per locus (A<jats:sub>e</jats:sub>), and expected heterozygosity (H<jats:sub>e</jats:sub>) 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. Partitioning of genetic diversity showed that 88.2% resided within populations. The proportion of genetic diversity among populations (G<jats:sub>st</jats:sub> = 0.118; F<jats:sub>ST</jats:sub> = 0.085) was either lower than or within the range of those species with similar ecological and life-history traits. The mean genetic identity 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 component analysis (PCA) were similar to those revealed by UPGMA. In addition, PCA separated the northernmost population (New York) from the major group. Sampling strategies for future germplasm collection of <jats:italic>A. triloba</jats:italic> are also discussed.</jats:p>

Inheritance of AFLP Markers and Their Use for Genetic Diversity Analysis in Wild and Domesticated Pawpaw [Asimina triloba (L.) Dunal]

“…Partitioning of the population genetic diversity showed that genetic diversity within populations accounted for 81.3% of the total genetic diversity based on dominant AFLPs. This result agrees with fi ndings of Huang et al (1998Huang et al ( , 2000 using isozymes and RAPDs that most of the genetic diversity of pawpaw resides within the wild population. Furthermore, the proportion of 18.7% genetic diversity observed among A. triloba populations is slightly lower than the average for species with wide geographic range (21.0%), insect outcrossing species (24.3%), species with animal-ingested seed dispersal mechanisms (12.4% to 27.7%) and reproduction modes (21.3% to 22.5%), and temperate species (24.6%) (Hamrick and Godt, 1989).…”

“…Neiʼs genetic diversity (Nei, 1973) across all the populations was 0.077 (ranging from 0.039 to 0.074) estimated by dominant markers ( Table 2). The genetic diversity estimated using dominant AFLP markers among wild populations was lower than those estimated by RAPDs (0.249 for H e and 64% for percentage of polymorphic loci) (Huang et al, 2000) and isozymes (0.172 for H e and 43.5% for percentage of polymorphic loci) (Huang et al, 1998). The low level of H e estimated using dominant AFLP markers was due to the large portion (72%) of monomorphic markers.…”

“…Several molecular-based analyses have been recently used to assess genetic diversity in pawpaw. These include a minisatellite probe (M13) (Rogstad et al, 1991), allozymes (Huang et al, 1997(Huang et al, , 1998, rapid amplifi cation of polymorphic DNA (RAPDs) (Huang et al, 2000(Huang et al, , 2003, and intersimple sequence repeats (ISSR) (Pomper et al, 2003). These previous studies determined that the genetic variation in both cultivated and wild pawpaws is comparable to those of other long-lived, temperate woody perennials.…”

Genetic Variation in Pawpaw Cultivars Using Microsatellite Analysis

“…In cherimoya (Annona cherimola), which is in the same family (Annonaceae), Escribano et al (2008) The development of superior pawpaw cultivars in terms of fruit quality and yield and the enhancement of genetic diversity contained in cultivars that are available to the public is crucial to the continued commercialization of pawpaw. High levels of genetic diversity exist in A. triloba (Huang et al, 1997(Huang et al, , 1998(Huang et al, , 2000Pomper et al, 2003Wang et al, 2005), which is consistent with frequent seed reproduction and adaptation of different environments. Grouping of genotypes in an unweighted pair group method with an arithmetic mean dendrogram showed that the PPF cultivars were more closely grouped with KSU advanced selections and that the older cultivars were genetically more distant than KSU or PPF selections unique genotypes.…”

“…A range of DNA and protein-based genetic marker systems has been used in attempts to evaluate genetic diversity in pawpaw. These marker systems include the minisatellite probe (Rogstad et al, 1991), allozymes (Huang et al, 1997(Huang et al, , 1998, random amplified polymorphic DNA [RAPD (Huang et al, 2000(Huang et al, , 2003], amplified fragment length polymorphism [AFLP (Wang et al, 2005)], intersimple sequence repeat [ISSR ], and SSR . Overall, these studies determined that the genetic variation in both cultivated and wild pawpaws is similar to those of other long-lived, temperate woody perennials characterized by a widespread geographic range, insect-pollinated outcrossing breeding systems, secondary asexual reproduction, and animal-dispersed seed.…”