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R. Neal Peterson

The pawpaw (Asimina triloba) is a new crop in the early stages of domestication. Recently commercialization has become feasible with the availability of high quality varieties. The history of pawpaw varieties is divided into three periods: 1900-50, 1950-85, and 1985 to the present. The history before 1985 was concerned primarily with the discovery of superior selections from the wild but experienced a serious break in continuity around 1950. The third period has been characterized by greater developmental activity. Larger breeding programs have been pursued, regional variety trials initiated, a germplasm repository established, and a formal research program at Kentucky State University (KSU) instituted. Future breeding will likely rely on dedicated amateurs with the education and means to conduct a 20-year project involving the evaluation of hundreds of trees. For the foreseeable future, governments and universities will not engage in long-term pawpaw breeding.

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Desmond R. Layne and R. Neal Peterson

In 1993, PPF and KSU embarked on a joint venture to test within pawpaw's native range many of the commercially available named pawpaw cultivars and PPF's advanced selections. Orchards for RVT were planted in 17 locations from Fall 1995 through Fall 1996 (possibly into 1997) consisting of 300 trees each. At each RVT site, eight replicate trees of each of the 28 grafted scion varieties will be tested in a randomized complete-block design. Named varieties that are secured for testing include Middletown, Mitchell, NC-1, Overleese, PA-Golden, Sunflower, Taylor, Taytwo, Wells, and Wilson. The other 18 clones to be evaluated originated in PPF orchards at the Univ. of Maryland Experiment Stations at Wye and Keedysville. Seedling trees from local native sources were planted around the perimeter as a buffer against edge effects and to allow comparisons with local germplasm. Identical orchards of the RVT are located in the following states: Arizona, Indiana, Iowa, Kentucky (two sites), Louisiana, Maryland, Michigan, Nebraska, New York, North Carolina, Ohio, Oregon, South Carolina, Tennessee (two sites), and the Chinese Academy of Forestry, Beijing, China. An orchard of nonidentical design is located in Florida. Additional sites in Connecticut and Chile are contemplated. Variables being studied in the trial include climate, culture, pests, growth, flowering, yield, and fruit characteristics. Trees will be evaluated for several years for yield, year-to-year consistency, regional suitability, etc. At the end of the trial period, regional recommendations will be made. Scion–rootstock compatibility based on percent scion take, scion growth (scion height and cross-sectional area), and first year field data are presented and discussed.

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Hongwen Huang, Desmond R. Layne, and R. Neal Peterson

The utility of isozyme phenotypes for identifying and determining genetic variation in pawpaw cultivars was studied using isoelectric focusing in thin-layer polyacrylamide gels. Based on a sample of 32 clones (cultivars and advanced selections) and 23 enzyme systems, 7 enzymes were found to be polymorphic, involving 9 polymorphic loci [acid phosphatase (ACP), dihydrolipoamide dehydrogenase (DDH), malic enzyme (ME), phosphoglucoisomerase (PGI), phosphoglucomutase (PGM), peroxidase (PRX), and shikimate dehydrogenase (SKD)]. Altogether these 9 loci and 32 clones yielded 28 multi-locus isozymic phenotypes useful for cultivar identification; 24 of the 32 clones were uniquely identified. The allozyme variation in these clones has the average of other long-lived woody perennials of widespread geographic range in temperate regions with insect-pollinated outcrossing breeding systems, secondary asexual reproduction, and animal-dispersed seed. Genetic differentiation among these pawpaw clones, measured by Nei's distance, D, was substantial: 496 pairwise comparisons of genetic distance among the 32 clones indicated that they differed on average of D = 0.068 ± 0.04 and ranged from 0 to 0.188. Cluster analysis (UPGMA) produced a most likely division of the 32 clones into 7 groups; however, these groups did not conform to known pedigree relations. Additional polymorphic enzymes are needed for accurate allozyme-based genetic discrimination.

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Kirk W. Pomper, Desmond R. Layne, R. Neal Peterson, and Dwight Wolfe

Beginning in 1993, 12 institutions and individuals and The PawPaw Foundation (PPF) embarked on a joint venture to evaluate commercially-available, named pawpaw (Asimina triloba) varieties and PPF's advanced selections within and outside of the pawpaw's native range. Each Pawpaw Regional Variety Trial (PRVT) planting, consists of about 300 trees, with five to eight replications (blocks) of 28 grafted scion varieties per block in a randomized complete block design (10 named varieties and 18 clones selected in the PPF orchards at the University of Maryland Experiment Stations at Queenstown and Keedysville, Md.). Variables being examined in the trial include climatic effect, culture, pests, growth, fl owering, yield, and fruit characteristics. In 1995, PRVT plantings were established in Kentucky (Princeton, Ky.), Louisiana, North Carolina, Oregon, and South Carolina. In 1998, a second planting was established in Kentucky (Frankfort, Ky.). In 1999, PRVT plantings were established in Indiana, Iowa, Michigan, Maryland, Nebraska, New York, and Ohio. In the Frankfort planting, 95% of the trees have survived. Based on height and trunk diameter measurements taken from 1998 to 2001, most selections displayed good vigor. The variety PA-Golden had the best early fruit production as evidenced by the fact that five of eight trees had fruit in 2001. In the Princeton, planting, only 54% of the trees have survived. The selections `Sunfl ower', `PA-Golden', `NC-1', `Wilson', 1-23, 8-20, and 9-58 showed the best fruit production and survival rates (>63%) in 2001. Based on limited data collected so far in the Kentucky trials, `PA-Golden' and `Sunfl ower' have performed well in the two locations and other varieties and PPF selections show promise.

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Sheri B. Crabtree, Kirk W. Pomper, Desmond R. Layne, and R. Neal Peterson

The pawpaw [Asimina triloba (L.) Dunal] is a tree fruit native to the eastern United States with potential as an alternative crop for small farmers. The Pawpaw Regional Variety Trial (PRVT) was established in 1993 by Kentucky State University (KSU) and the PawPaw Foundation (PPF) and includes 28 cultivars and advanced selections planted at 12 sites. The PRVT was established at the KSU Research Farm in Frankfort, Ky., in 1998. Data has been collected on the KSU-PRVT annually since its inception. The first fruit were produced in 1999, with Middletown, Mitchell, Overleese, and Sunflower being the most precocious varieties. A frost occurred in early April 2000, decimating the crop, with only eight fruit being produced across the orchard. In 2001, 12% of the trees produced fruit, with PA-Golden having the best early production. In 2002, 68% of trees in the PRVT fruited, producing a total of 3,500 fruit. Selections with the largest fruit (over 200 g) were Susquehanna, 5-5, 4-2, and 1-7-2. In 2003, a spring frost destroyed most of the flowers and developing fruit. Only 32 out of the 224 trees in the PRVT retained fruit, a total of only 131 fruit in the entire orchard. In 2004, the PRVT produced about 25,000 fruit across the entire orchard. Selections 4-2 and 7-90 produced the largest fruit, over 200 g. Shenandoah, 10-35, and 8-20 were the highest-yielding clones, all producing over 15 kg of fruit per tree. In 2005, spring frosts and a severe summer drought diminished fruit set and retention in the PRVT, with the orchard producing 8,900 fruit. Selections 4-2, 5-5, and Susquehanna produced the largest fruit, all weighing over 200 g. The highest yielding selections were 10-35, PA-Golden, and 1-7-2, all producing over 8 kg of fruit per tree.

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Kirk W. Pomper*, Joseph G. Masabni, Desmond R. Layne, Sheri B. Crabtree, R. Neal Peterson, and Dwight Wolfe

The pawpaw [Asimina triloba (L.) Dunal] has great potential as a new fruit crop. A pawpaw variety trial was established in Fall 1995 in Princeton, Ky. as a joint Kentucky State Univ.-Univ. of Kentucky research effort with the objective to identify superior varieties for Kentucky. A randomized block experimental design was used with 8 replicates of 28 grafted scion selections on seedling rootstock. Cultivars being tested included Middletown, Mitchell, NC-1, Overleese, PA-Golden, Rappahannock, Shenandoah, Sunflower, Susquehanna, Taylor, Tay-two, Wells, and Wilson. The other 15 clones were selections from the PawPaw Foundation. In 2002 and 2003, the following parameters were examined: tree survival, trunk cross-sectional area (TCSA), average fruit weight, total fruit harvested per tree, average fruit per cluster, total yield per tree, and yield efficiency. In 2003, 54% of the trees had survived, with `Susquehanna' (13%) showing the poorest survival. Based on TCSA, most selections displayed excellent vigor, with the exception of the selections: 5-5 and `Overleese'. Average fruit weight was greatest in 1-7-2 (194 g), 1-68 (167g), 4-2 (321 g), 5-5 (225 g), 7-90 (166g), 9-58 (176 g), 10-35 (167 g), NC-1 (180 g), `Sunflower' (204 g), and `Shenandoah' (168g), with the smallest fruit in `Middletown' (70 g), `Wells' (78 g), and `Wilson' (88 g). The selections `Wilson' (81), `Middletown' (75), and `Wells' (70) had the greatest average number of fruit per tree, whereas 4-2 (9), 5-5 (17) and 8-20 (15) the fewest. Yield efficiency and average fruit per cluster also varied greatly among selections. Several pawpaw selections in the trial show promise for production in Kentucky.