The American persimmon (Diospyros virginiana) is a slow-growing, moderately sized tree-fruit native to the forests of the southeastern and midwestern United States (Nesom, 2018) and is in the early stages of commercial orchard production (Skallerup, 1953). The American persimmon is tolerant to a range of soil conditions and trees have a long productive life of more than 20 years (Goodell, 1982; McDaniel, 1973a, 1973b; Troop, 1895). Overall, American persimmon is well adapted to low input culture by small growers with few pests and diseases (Kaiser and Ernst, 2017; Nesom, 2018; Crandall and Baker, 1950; Kaiser and Ernst, 2017).
The American persimmon matures over a long ripening season, and trees have a long, productive life (McDaniel, 1973a, 1973b). The golden-orange fruit are sweet when fully ripe and astringency is reduced. A common misconception is that the persimmon fruit is not edible and less astringent until it has frozen, but this is not the case with most cultivars (Troop, 1895). The fruit is well suited for processing and preservation by freezing. Its pulp can be used in pudding, cookies, cake, custard, and ice cream (Briand, 2005; Goodell, 1982). Ground persimmon seeds have been used as a substitute for coffee (Briand, 2005) and tea made from the leaves of persimmon has antioxidant properties (Kobayashi et al., 2017). Flowers are a significant nectar source for bees (Troop and Hadley, 1895). The most widely cultivated persimmon species across the world is Diospyros kaki, the Oriental or Japanese persimmon, with its large, light yellow-orange to dark red-orange nonastringent fruit; however, this species is not well adapted to the Kentucky climate, and cultivars do not share a similar genetic background (Ames, 2010; Raddová et al., 2012).
American persimmon improvement began in the late 19th century with the work of Dr. James Troop at Purdue University (Plumb, 1896; Troop, 1895; Troop and Hadley, 1895). The first named American persimmon cultivar was selected out of the wild in Illinois in 1880 (Miller, 1894). This original cultivar, Early Golden, has served as the female parent of many of the cultivars developed throughout the 20th century. Professor J.C. McDaniel (1973a) from the University of Illinois had a strong interest in persimmon and was responsible for selecting the cultivars John Rick and Florence. James Claypool continued breeding American persimmon in the 1970s (Goodell, 1982). Over the course of 20 years, Claypool evaluated more than 2000 trees and kept extensive orchard records describing the characteristics of each tree in his breeding project (Jerry Lehman, personal communication). Some of the Claypool selections are commercially available from nurseries.
Troop and Hadley (1895) reported that American persimmons are normally dioecious and require cross-pollination with another cultivar to produce fruit. At least three American persimmon cultivars, Early Golden, Gatterson, and Killen, are usually pistillate (female-flower) trees; however, some branchlets of staminate (male) flowers occur and can furnish pollen for fruit set (McDaniel, 1973a, 1973b).
There are two races of American persimmon: a tetraploid (60-chromosome) race is centered in the southern Appalachian Mountains and adjacent areas and a hexaploid (90-chromosome) race occupies the range north and west of the tetraploid range (Fig. 1). Using light microscopy observation of root tips stained with crystal violet, hexaploid genotypes were identified for plants generated from seeds collected from trees in Delaware, Georgia, Iowa, Kansas, Louisiana, Mississippi, Missouri, Ohio, Pennsylvania, Texas, Virginia, and West Virginia, whereas tetraploid genotypes were identified from sites in Florida, Georgia, Kentucky, North Carolina, South Carolina, and Tennessee (Baldwin and Culp, 1941). This study included only single tree samples of seeds for most states, although several additional trees were sampled in Georgia, Tennessee, Texas, and Virginia. The ranges for persimmons with these two ploidy levels overlap in Kentucky (Baldwin and Culp, 1941).
Most cultivated American persimmon cultivars are considered likely to be the northern hexaploid race; however, there has not been a thorough examination of ploidy level for commercially available cultivars (Choi et al., 2003; McDaniel, 1973a; Nissen and Roberts, 2015). This study is the first to examine the contribution of the tetraploid race toward the commercially available cultivar base. Because both ranges overlap, pollen from a different race with a different pollen ploidy number would result in sexual incompatibility, resulting in pollination without fertilization and the production of seedless fruits. This could allow for the development of orchard production with staminate tetraploid race trees with hexaploid pistillate cultivars to produce seedless fruit. McDaniel (1973a) noted that trees of ‘Wabash’, a hexaploid, ripen seedless fruit when pollinated by tetraploid males. McDaniel (1973b) noted that seedless fruits of American persimmon do not have as edible a quality because seeded fruits on the same clone and seedless clones are consistently inferior in sweetness to the best seeded cultivars. The objective of this study was to assess the ploidy level of commercially available American persimmon cultivars and native Kentucky persimmon populations to compare tetraploid and hexaploid contributions to this germplasm for grower knowledge.
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