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by the enthusiasm of individuals in the Northern Nut Growers Association (NNGA) (Peterson 2003). Since 1985, various associations and institutions committed to pawpaw development have emerged. The PawPaw Foundation (PPF) was founded in 1988, by R. Neal Peterson, as a nonprofit organization dedicated to the research and development of the pawpaw as a new fruit crop for farmers and consumers. In 1990, a full-time pawpaw research program was initiated at Kentucky State University (KSU) by Brett Callaway (Callaway 1992) and was expanded by Desmond Layne from 1993 to 1997 (Layne 1996) and has been under the direction of Kirk Pomper since 1998 (Pomper et al. 1999). For over 10 years at KSU there have been cooperative research projects with PPF to advance our understanding of the pawpaw. Two international pawpaw conferences have been held. The first conference was held in 1994 at the Western Maryland Research and Education Center in Keedysville, Maryland, where about 45 scientists, nurserymen, entrepreneurs, and enthusiasts attended. The second conference was held at KSU in Frankfort, Kentucky and had over 130 people in attendance (Pomper et al. 2003a). The Ohio Pawpaw Growers Association (Albany, Ohio) was established in 2000 to organize and advance the development of a pawpaw industry in Ohio. The Ohio Pawpaw Growers Association, PPF, and the KSU pawpaw program, as well as other associations and institutional programs that will likely be established, will be important in promoting, marketing and consumer education programs concerning pawpaw.
The tropical custard apple family, Annonaceae, is the largest primitive family of flowering plants, containing approximately 130 genera and 2300 species (Conquist 1981). This family includes several delicious tropical fruits such as the custard apple (Annona reticulata L.), cherrimoya (A. cherimola Mill.), sweetsop or sugar apple (A. squamosa L.), atemoya (A. squamosa × A. cherimola), and soursop (A. muricata L.) (Bailey 1960). The genus Asimina is the only temperate-zone representative of the tropical Annonaceae, and includes nine species, most of which are native to the extreme southeastern regions of Florida and Georgia (Kral 1960; Callaway 1990, 1993). These species include Asimina incarna (Bartr.) Exell. (flag pawpaw), A. longifolia Kral, A. obovata (Willd.) Nash, A. parviflora (Michx.) Dunal (dwarf pawpaw), A. pygmaea (Bartr.) Dunal, A. reticulata Shuttlw. ex Chapman, A. tetramera Small (opossum pawpaw), A. × nashii Kral and A. triloba (Kral 1960). All
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Asimina species are diploids, $ 2n = 2x = 18 $, with the possible exception of A. pygmaea (Bartr.) Dunal, for which chromosome counts have not been reported (Bowden 1948; Kral 1960). Triploid A. triloba hybrids have also been reported to exist (Bowden 1949).
The genera of Annonaceae have been difficult to separate; therefore, the pawpaw has undergone a number of nomenclature changes (Kral 1960). Linnaeus first classified it as Annona triloba in 1753. Ten years later, Adanson assigned the pawpaw to the Asimina genus. It remained in this classification for several years, until 1803 when Michaux reclassified pawpaw as Orchidocarpum arietinum. Four years later Persoon reclassified it as Porcelia triloba. In 1817 Dunal returned pawpaw to Asimina, but Torrey and Gray transferred it to the genus Uvaria in 1838. In 1886, Gray reconsidered the classification and returned pawpaw to Asimina. Asimina triloba (L.) Dunal is the nomenclature currently accepted (Kral 1960).
The large-fruited pawpaw, Asimina triloba, is likely the best-known member of the Asimina genus. This species has the most northerly and largest native range of the genus, extending from northern Florida to southern Ontario, Canada, and as far west as eastern Nebraska and Texas (Kral 1960; Callaway 1990, 1993). The fruit of A. triloba has the greatest commercial potential of the Asimina genus due to the large size and usually pleasing flavor.
Pawpaw is a moderately small, deciduous tree or shrub that flourishes in the deep, rich fertile soils of river-bottom lands of the forest understory (Kral 1960). Trees may attain 5 to 10 m in height and are usually found in patches, due to root suckering (Kral 1960; Layne 1996). In sunny locations, trees typically assume a pyramidal habit, with a straight trunk and lush, dark-green, long, drooping leaves. Leaves occur alternately, are obovate-oblong in shape, glabrous, with a cuneate base, acute midrib, and may be 15 to 30 cm long and 10 to 15 cm wide. Vegetative and flower buds occur at different nodes on the stem, the flower buds being basipetal. Vegetative buds are narrow and pointed, and the flower buds are round and covered with a dark-brown pubescence.
The dark maroon-colored flowers of the pawpaw are hypogynous and strongly protogynous (Willson and Schemske 1980). Flowers are pendant on nodding, with sturdy pubescent peduncles up to 4 cm long (Kral 1960). The mature flowers have an outer and inner whorl of three, maroon-colored, three-lobed petals (Fig. 7.1). The inner petals are smaller and fleshier, with a nectary band at the base. The flower has a fetid aroma. Flowers have a globular androecium and a gynoecium usually