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- Author or Editor: Jeremiah D. Lowe x
Pawpaw [Asiminatriloba (L.) Dunal] is a tree fruit native to areas in the Midwest and Southeast United States. Since 1994, Kentucky State University (KSU) has served as the USDA National Clonal Germplasm Repository, or gene bank, for pawpaw; therefore, the assessment of genetic diversity in pawpaw is an important research priority for the KSU program. There are over 1800 pawpaw accessions (trees) from 16 different states and over 40 cultivars that are planted on 8 acres at the KSU farm. The objectives of this study were to develop microsatellite markers for pawpaw, and to then use those markers to evaluate 19 cultivars in the repository collection. Leaves of the pawpaw cultivar Sunflower were sent to Genetic Information Systems (Chatsworth, Calif.) for simple sequence repeat (SSR) primer and marker development. A total of 34 microsatellite primers were developed for pawpaw. These primers were then used in a preliminary screening with five pawpaw cultivars (`Sunflower', `Mitchell', `Sweet Alice', `Overleese', and `Prolific'). Results from this preliminary screening indicate that four of the primers failed to amplify any product, 12 primers were monomorphic, and 18 primers were polymorphic. Eleven additional cultivars were then screened, which produced numerous polymorphic products. For example, Primers B3 and B118 produced products ranging in size from 490 to 350 bp. Polymorphic products will be used to examine genetic variation among the pawpaw cultivars screened.
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.
The American persimmon (Diospyros virginiana) is a slow-growing, moderately sized tree fruit native to the forests of Kentucky. This tree fruit is in the early stages of commercial production with many cultivars selected from the wild. Small orchards of commercially available cultivars are planted in Kentucky. Persimmons are normally dioecious, and female trees require cross-pollination to produce fruit. There are two races of persimmon: the tetraploid (60-chromosome) race is centered in the southern Appalachian region, while the hexaploid (90-chromosome) race generally occupies a range north and west of the tetraploid range. These ranges overlap in Kentucky. Because the ranges overlap, cross-pollination may cause sexual incompatibility, resulting in pollination without fertilization, and therefore seedless fruits of poor quality. The objective of this study was to assess the ploidy level of commercially available American persimmon cultivars and native Kentucky persimmon populations. Leaf samples were collected from 45 cultivars and advanced selections, as well as 45 trees from native populations in Bullitt, Barren, and Franklin Counties. Flow cytometer analysis showed that only four of the selected cultivars were from the tetraploid race: Ennis Seedless, Weeping, Sugar Bear, and SFES; the remaining cultivars were from the hexaploid race. Both hexaploid and tetraploid American persimmon trees were identified in the populations sampled in the Bullitt County locations, but only tetraploid races were found in Franklin and Barren Counties. Because pollen from native trees could result in seedless fruit formation of poor quality when native seedlings are used as pollinizers in commercial production of American persimmon, ploidy level of seedlings needs to be considered.
Pawpaw [Asimina triloba (L.) Dunal.], a tree fruit native to eastern North America, is in the beginning stages of commercialization. Cultivars available in the early 20th century have been lost, and significant genetic erosion may have occurred. Polymorphic microsatellite marker loci were developed from enriched genomic libraries. Five marker loci were used to fingerprint 28 cultivars and 13 selections. For the 41 genotypes, 102 alleles were amplified and major allele frequency (0.16–0.94), number of genotypes (2–27), and allele size (144–343 bp) varied greatly by locus. Four loci were highly polymorphic, as indicated by values for expected heterozygosity (He), observed heterozygosity (Ho), and polymorphism information content, but only two alleles were detected at locus Pp-C104. A high level of genetic diversity was observed in the studied genotypes. The Ho (0.68) and He (0.70) were similar and indicated few null alleles. In the 41 genotypes, 39 unique fingerprints were observed. These new microsatellite marker loci will be useful for cultivar fingerprinting, management of collections, and investigation of genetic diversity in collections and wild populations. Grouping of genotypes in an unweighted pair group method with arithmetic mean dendrogram was generally consistent with their origins.