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  • Author or Editor: Kirk W. Pomper x
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Pawpaw [Asimina triloba (L.) Dunal] is a highly perishable climacteric fruit, softening rapidly once ripening commences which may limit its marketability. In studies to determine the optimum cold storage temperature and maximum storage life of the fruit, pawpaw fruit were stored at -2, 2, and 6 °C for 1, 2, 4, 8, and 12 weeks, and then ripened upon removal to ambient temperature. Through 4 weeks, fruit exhibited adequate firmness upon removal from cold storage, but at 8 and 12 weeks fruit held at 2 and 6 °C were very soft. Irrespective of storage temperature, at 8 weeks fruit showed a delay in a climacteric-like respiratory increase, and by 12 weeks a respiratory climacteric was not apparent. An ethylene climacteric was evident after all temperature and storage periods except those held at 6 °C for 12 weeks. Significant symptoms of cold injury were found by 8 weeks of 2 °C cold storage. In addition to a delayed respiratory climacteric, pawpaw fruit stored for 8 and 12 weeks exhibited flesh browning within 48 h of moving to ambient temperature. A change in fruit aroma volatile profile suggested injury might have been developing by 4 weeks of cold storage even though other symptoms were not evident. Immediately after harvest, methyl octanoate was the dominant volatile ester followed by methyl hexanoate. By 4 weeks of postharvest cold storage, ethyl hexanoate was the dominant ester followed by ethyl octanoate, but methyl octanoate production was still substantial. At 8 weeks, volatile ester production was generally lower with ethyl hexanoate the major volatile followed by ethyl octanoate. These symptoms indicate that pawpaw fruit can suffer cold injury during extended periods of cold storage.

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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.

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Marketed as a fresh fruit, the pawpaw (Asimina triloba) has a short shelf life, only 2-3 days at room temperature and up to 3 weeks with refrigeration. There is commercial processing potential for pawpaw pulp in juices, ice cream, yogurt, baked goods, and other products. Consumer acceptability of such products needs to be investigated. One hundred and five attendees of the 2nd Annual Pawpaw Field Day at Kentucky State University (KSU), Frankfort, Ky., participated in a tasting of pawpaw products; 56% of tasters were male; 76% were over 40 years of age; 72% of tasters had eaten pawpaw previously. Each item was rated on a scale from 1 = liked it extremely to 7 = disliked it extremely. Pawpaw ice cream was the best-received item (55% of tasters liked it extremely), followed by pawpaw cake with lemon icing, liked extremely by 45%. The pawpaw/grape juice drink was liked extremely by 31% of participants. Three alternative recipes for pawpaw butter were presented; the plain pawpaw butter was liked extremely by 26% of tasters; pawpaw butter prepared with lemon and grape juice was liked extremely by 11%, while the version prepared with orange and lemon was liked extremely by only 8%. Two versions of pawpaw custard were presented. The custard prepared from ripe, mild-fl avored fruit was liked extremely by 42% of tasters, while the custard prepared from mixed under-ripe, over-ripe and bruised fruit was liked extremely by only 16%. Ratings by persons unfamiliar with pawpaw fl avor were significantly lower (P < 0.05) only for the two pawpaw custards; tasters age 40 years or younger gave significantly higher ratings for pawpaw ice cream (P < 0.05) and significantly lower ratings for both pawpaw custards (select, P < 0.05 and mix, P < 0.01) and the pawpaw/grape juice drink (P < 0.05).

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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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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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The pawpaw [Asimina triloba (L.) Dunal] is a native plant found mainly in the southeastern and eastern United States, and its fruit has great potential as a new high-value crop in these regions. Although there are ≈45 named pawpaw cultivars, breeding for improvement of specific traits, such as fruit size and quality, is desirable. Our long-term goal is to utilize molecular marker systems to identify markers that can be used for germplasm diversity analyses and for the construction of a molecular genetic map, where markers are correlated with desirable pawpaw traits. The objective of this study was to identify random amplified polymorphic DNA (RAPD) markers that segregate in a simple Mendelian fashion in a controlled A. triloba cross. DNA was extracted from young leaves collected from field-planted parents and 20 progeny of the cross 1-7 × 2-54. The DNA extraction method used gave acceptable yields of ≈7 μg·g-1 of leaf tissue. Additionally, sample 260/280 ratios were ≈1.4, which indicated that the DNA was of high enough purity to be subjected to the RAPD methodology. Screening of 10-base oligonucleotide RAPD primers with template DNA from the parents and progeny of the cross has begun. We have identified two markers using Operon primer B-07 at 1.1 and 0.9 kb that segregate in a simple Mendelian fashion in progeny of the 1-7 × 2-54 cross. Other primers and controlled crosses will also be screened.

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Pawpaw [Asimina triloba (L.) Dunal] is a native American fruit tree that has potential as a new fruit crop or for use in landscapes, but little information is available to nurseries on the production of containerized plants. In greenhouse experiments, growth of pawpaw seedlings in Rootrainers was examined in three fertilization regimes, two root-zone temperatures, and four substrates [ProMix, 6 pine bark: 1 sand (v/v), 1 sand: 1 sphagnum peat, and 4 pine bark: 1 sand: 1 sphagnum peat medium]. A similar germination rate of 80% was obtained in all substrates. Weekly fertigation treatments were imposed when seedlings had 2 to 3 leaves, at 0, 50, and 100 mg·L-1 N as Peters 20N-8.6P-16.6K water-soluble fertilizer plus soluble trace elements. After 140 days at the highest fertilizer rate, plant height, leaf number, and dry weight (roots, shoots, and total plant) were greater in ProMix and 1 sand:1 sphagnum peat than in 6 pine bark: 1 sand (v/v) or 4 pine bark: 1 sand: 1 sphagnum peat. Also, the root: shoot ratio was lower in ProMix and 6 pine bark: 1 sand (v/v). Overall, plant biomass production was greater in ProMix than in 6 pine bark: 1 sand (v/v). In a separate experiment, bottom heat (32 ± 0.3 °C) hastened seedling emergence from ProMix by 9 days compared to ambient root-zone conditions (24 ± 0.2 °C). An average seedling height of 10 cm was attained by ambient plants 79 days after sowing, whereas seedlings with bottom heat reached this height after 69 days. Seedlings subjected to bottom heat had increased leaf number (30%), plant height (32%), whole plant leaf area (94%), shoot dry weight (104%), root dry weight (50%), lateral root dry weight (125%), and total plant dry weight (87%). Seedlings with bottom heat had a reduction in root: shoot ratio of 25% and in specific leaf dry weight of 16% compared to ambient plants. Seedlings subjected to bottom heat had a higher leaf chlorophyll (chl) concentration of chl a (39%), chl b (33%), chl p (43%), total chl (38%), and chl a: b ratio (8%) than seedlings grown without bottom heat. Pawpaw seedling growth was best using ProMix with 100 mg·L-1 N Peters applied once weekly, or using ProMix with bottom heat and 50 mg·L-1 N Peters applied twice per week.

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The genus Asimina has the only temperate representatives of the tropical Annonaceae, or Custard Apple family, and includes eight species that are indigenous to North America. The North American pawpaw Asimina triloba (L.) Dunal has the largest edible fruit native to the United States and is the best-known of these species. The USDA National Clonal Germplasm Repository for Asimina species is located at Kentucky State Univ. (KSU); therefore, assessment of genetic diversity is an important research priority for KSU. The inter-simple sequence repeat PCR (ISSR-PCR) methodology has been used successfully to characterize genetic diversity within and among populations of many plant species. The objective of this study was to assess the utility of ISSR markers in evaluating genetic relationships in members of the Asimina genus, as well as closely related tropical relatives in the Annona genus. Leaf samples were collected from three plants each of Asimina longifolia, A. obovata, A. parviflora, A. reticulata, A. tetramera and A. triloba. Leaf samples were also collected from three plants each of Annona cherimola, A. squamosa, A. reticulata, A. muricata, A. glabra, A. diversifolia, and A. montana. DNA was extracted from leaf samples and subjected to ISSR-PCR using the REDExtract-N-Amp™ Plant PCR Kit. DNA samples were screened with ISSR primers using the Univ. of British Columbia microsatellite primer set #9. Three primers, UBC812, UBC841, and UBC873 were found to produce 84 scorable ISSR markers and allowed the determination of genetic relationships among Asimina and Annona members examined.

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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.

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The pawpaw [Asimina triloba (L.) Dunal.] is a tree fruit native to many areas of the southeastern and mid-western United States. Kentucky State University (KSU) is designated as a satellite repository for Asimina for the U.S. Department of Agriculture (USDA), National Plant Germplasm System (NPGS). An assessment of the level of genetic diversity in cultivated pawpaw would assist in development of the future germplasm repository collection strategies for cultivar improvement. The objectives of this study were to identify intersimple sequence repeat (ISSR) markers that segregate in a simple Mendelian fashion and to use these markers to assess genetic diversity in 19 pawpaw cultivars. Leaf samples from the 34 progeny of controlled crosses (1-7-1 × 2-54 and reciprocal) and the parents were collected, DNA was extracted, and subjected to the ISSR methodology using the University of British Columbia microsatellite primer set #9. Seven primers yielded 11 Mendelian markers with either a 3:1 or 1:1 ratio that was confirmed by chi-square analysis. Analysis of genetic diversity using 10 of the ISSR markers from 19 pawpaw cultivars revealed a moderate to high level of genetic diversity, with a percent polymorphic loci P = 80 and an expected heterozygosity He = 0.358. These diversity values are higher than those reported for cultivated pawpaw using isozyme or randomly amplified polymorphic DNA (RAPD) markers, indicating that the ISSR marker methodolgy has a higher level of discrimination in evaluating genetic diversity in pawpaw and/or pawpaw has greater levels of genetic diversity than previously found.

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