Genetic variation in pawpaw cultivars using microsatellite analysis

Abstract

Pawpaw (Asimina triloba) is a tree fruit native to eastern North America, which is in the early stages of domestication. Most early 20th century pawpaw cultivars have been lost; however, recent cultivar releases and potential new releases may have enhanced genetic diversity. The objective of this study was to compare the genetic variation exhibited among older and new pawpaw cultivars and Kentucky State University (KSU) advanced selections using simple sequence repeat (SSR) markers. Polymorphic microsatellite marker analysis was conducted with nine older pawpaw cultivars, six recently released PawPaw Foundation (PPF) cultivars, and nine KSU advanced selections. Using 18 microsatellite loci, a total of 179 alleles were amplified in the set of 24 genotypes. The major allele frequency (0.13 to 0.96), number of genotypes (two to 23), and allele size (96 to 341 bp) varied greatly by locus. Eighteen loci were highly polymorphic, as indicated by high expected heterozygosity (He = 0.71) and observed heterozygosity (Ho = 0.65) values as well as high polymorphism information content (polymorphism information content = 0.69). The dinucleotide SSR (GA and CA motifs) loci were more polymorphic than trinucleotide (ATG and AAT motifs) SSRs. The PPF cultivars and KSU advanced selections were more closely grouped genetically than with older cultivars. Older cultivars displayed the greatest genetic diversity (Ho = 0.69). The pawpaw cultivar base of older and PPF cultivars does appear to be genetically diverse. However, KSU advanced selections contain unique pawpaw germplasm that should enhance the genetic base of cultivars if these selections are released to the public.