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  • Author or Editor: Desmond R. Layne x
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Replicated trials were conducted in summers of 1998 and 1999 at several commercial orchards to determine the influence of a metalized, high-density polyethylene reflective film (SonocoRF, Sonoco Products Co., Hartsville, S.C.) on fruit red skin color and maturity of peach cultivars that historically have poor red coloration in South Carolina. At each site there were two experimental treatments: i) Control; and ii) Reflective Film (RF). RF was laid 2 to 4 weeks before anticipated first pick date by laying a 5-ft-wide strip of plastic on either side of the tree row in the middles. Treatment blocks at a given farm ranged from 0.5 to 1 acre in size and each treatment was replicated four times at each site. At harvest, two 50-fruit samples were picked from each block per treatment. All fruit were sized and visually sorted for color (1 = 0% to 25%, 2 = 26% to 50%, 3 = 51% to 75%, and 4 = 76% to 100% red surface, respectively). A 10-fruit subsample was selected following color sorting and evaluated for puncture pressure and soluble solids concentration (SSC). All cultivars tested (CVN1, Loring, Bounty, Summer Gold, Sun Prince, Cresthaven, and Encore) experienced significant increases in percent red surface when RF was used in 1998 and 1999. This color improvement ranged from 16 to 44% (mean = 28%). On average, fruits from RF were 0.8 lb softer and had 0.3% higher SSC than control fruits. Growers harvested more fruit earlier and in fewer picks for RF. Fruit size was not affected by RF. The influence of RF on orchard microclimate and quality and quantity of reflected light will be discussed.

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Kentucky State Univ. (KSU) is the national clonal germplasm repository for Asimina species. Previous evaluation of the KSU pawpaw collection using 24 isozyme markers demonstrated that pawpaw has a relatively higher genetic diversity than that noted for other plant species with similar species characteristics (long-lived, woody, perennial, out-crossing, temperate, widespread, etc.). Current evaluation using RAPD markers will provide us with a more-accurate insight into pawpaw genetic diversity and population structure. In a preliminary experiment, one hundred 10-mer primers (OA1-20 through OE1-20, Operon Technologies Inc.) were screened against 32 commercial cultivars or advanced selections. A subset of 24 primers that amplify only the most-informative markers were used for germplasm evaluation. Sixty-eight RAPD markers were identified and used for determining genetic parameters. One-hundred-twenty pawpaw accessions were sampled from the KSU repository for RAPD analysis. These accessions represented nine widely distributed states within pawpaw's native range. RAPD data were subjected to various analyses using the NTSYS-PC computer program (ver. 1.8). Information generated from isozyme and RAPD markers will be used to formulate future germplasm collection strategies from wild populations within the native range. The implications of such information to the genetic enhancement of our repository and establishment of a core collection will be discussed.

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The North American pawpaw [Asimina triloba (L.) Dunal], a temperate member of the Annonaceae, is a deciduous woody tree with ornamental value and has merit as a fruit crop. Anatomical studies of pawpaw seed revealed a small, linear embryo that does not change in length during cold or warm stratification. Radicle and cotyledon growth from planting until radicle protrusion was concurrent and at about the same rate. Cotyledons grew through a specialized channel of cells extending above the cotyledon tips, but never emerged from the seed. The extended period of time required for the development of the cotyledons delayed seedling emergence more than 50 days. The cotyledons appear to be haustorial and translocate storage material from the endosperm to the growing embryo. At the time of epicotyl elongation, the radicle and developing root system were well developed and comprised 81 % of the seedling biomass. Seedling development could be divided into four distinct stages, including radicle protrusion, hypocotyl emergence, epicotyl elongation, and seedcoat abscission.

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The role of incident light intensity (light) and fertilization regime (Fert) on early growth and development of pawpaw seedlings in the greenhouse was investigated. Three-hundred and fifty stratified seeds were sown in 45 cubic inches. Rootrainer cells in Promix BX potting medium. A two-factor factorial design was used. Light was either ambient (Amb) or 80% shaded (Shade) Fert was 500 ppm of Peter's 20N–20P–20K plus soluble trace elements (+ Fert) or water (–Fert) applied twice weekly to runoff. Thirty uniform seedlings were selected at the two- to three-leaf stage for each of the four treatments. Treatment imposition was for 5 weeks until the 10- to 11-leaf stage (when seedlings would be transplanted). Plant height and leaf number was recorded three times weekly. After 5 weeks, 15 uniform plants per treatment were destructively harvested and leaf chlorophyll (chl) analysis was performed. Amb/+ Fert plants were 25% taller and had two more unfolded leaves, on average, than the other treatments.–Fert plants (Amb or Shade) had set terminal buds. The effect of Fert on chl was much greater under Amb than Shade conditions. For–Fert plants, total chl was reduced by 52% under Amb but only 30% under Shade compared to +Fert plants. Total biomass for Amb/–Fert seedling was double that in either Shade treatment and 40% greater than for Amb/–Fert seedlings.

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Growth of pawpaw (Asimina triloba) seedlings in containers was examined in a factorial greenhouse experiment with four treatment levels of the slow-release fertilizer, Osmocote 14-14-14 (14N- 6.1P-11.6K), incorporated in Pro-Mix BX potting substrate at 0, 0.13, 0.26 or 0.81 kg·m-3 (0, 0.22, 0.44, or 1.37 lb/yard3) and three treatment levels of liquid-feed fertilizer of Peters 20-20-20 (20N-8.7P-16.6K) water-soluble fertilizer at 0, 250, or 500 mg·L-1 (ppm). When plants were harvested 18 weeks after sowing, seedlings subjected to the highest rate of Osmocote 14-14-14 at 0.81 kg·m-3 and liquid-feed at 500 mg·L-1 had the greatest total biomass, about 3-fold greater than nonfertilized plants. In a separate greenhouse experiment, growth of seedlings was examined with Osmocote 14-14-14 as the sole fertilizer source at six treatment levels of: 0, 0.81, 2.22, 4.43, 8.86, or 17.7 kg·m-3 (0, 1.37, 3.74, 7.47, 14.9, or 29.9 lb/yard3). Early seedling growth was hastened in the 2.22 kg·m-3 treatment rate, but delayed in 17.7 kg·m-3 treatment rate, when compared to nonfertilized control plants. When seedlings were harvested 17 weeks after sowing, plants had the greatest shoot, root, and total dry weight with Osmocote 14-14-14 at a rate of 2.22 kg·m-3. Root:shoot ratio decreased from about 1.5 without Osmocote 14-14-14, to about 0.65 at rates of 2.22 kg·m-3 or greater. Based on the results of this study, the slow-release fertilizer, Osmocote 14-14-14, can be used effectively as a sole fertilizer source when incorporated into potting substrate at a rate of 2.22 kg·m-3 or at a reduced rate of 0.81 kg·m-3 when supplemented with weekly applications of liquid-feed fertilizer at a rate of 500 mg·L-1 of Peters 20-20-20, to enhance production of container-grown pawpaw seedlings.

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Replicated trials were conducted in Summers 1998 and 1999 at two commercial orchards (A and B) to determine the influence of a metalized, high density polyethylene reflective film (SonocoRF) and aminoethoxyvinylglycine (ReTain), on fruit red skin coloration and maturity of `Gala' apples (Malus sylvestris var. domestica). There were four experimental treatments: 1) nontreated control; 2) reflective film (RF); 3) ReTain; and 4) RF + ReTain. RF was applied 4 weeks before anticipated start of harvest by laying a 5-ft-wide (150-cm) strip on each side of the tree row in the row middle. ReTain was applied 4 weeks before harvest at the commercial rate in one orchard and at 60% of the commercial rate in a second test. ReTain delayed fruit maturity. Fruit from RF trees had a significantly greater percent surface red color than fruit from trees not treated with RF. Fruit from RF + ReTain were significantly redder and had higher soluble solids concentration (SSC) than fruit from trees treated with ReTain alone. There were no differences in size, fruit firmness or starch content between fruit from RF and RF + Retain. RF appears to be a method to increase red skin coloration in `Gala' apples treated with ReTain without adversely impacting maturity.

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Armillaria root rot (ARR) of peach caused by the soil-borne basidiomycete fungus Armillaria tabescens is causing premature decline and mortality of peach trees on most southeastern U.S. peach farms. Soil inoculum may be present both in former peach orchard sites and on sites that were once in hardwood forest. The fungus is protected under the bark of dead root pieces and may survive up to 100 years at various depths in the soil profile. No commercially available rootstocks are resistant to ARR. Since 2002, we have embarked on a multipronged strategy to develop control options to combat ARR. First, we have two replicated trials on commercial grower replant sites with a history of ARR. Trial 1 compares four preplant fumigation treatments (none, Telone II, methyl bromide, and Enzone), three rootstocks (Lovell, Halford, and Guardian) and preplant root dips with endomycorrhizal fungi. Trial 2 compares the use of raised beds, root collar excavation and preplant root dips. Both trials examine long-term productivity and tree survival. Second, we are examining the use of systemic fungicide injection into infected trees to protect trees around infection foci. Third, we are trying to develop a genetically modified ARR-resistant rootstock. We have inserted the gene encoding the gastrodia antifungal protein (GAFP—a low molecular weight lectin that binds mannose and chitin) from a Chinese orchid into tobacco (model herbaceous system) and plum (model Prunus system). GAFP has antifungal activity against several basidiomycete root rot pathogens. Pathogenicity tests with transformed tobacco plants show enhanced tolerance to several root rot pathogens when compared to nontransformed plants. Transformed plums are being multiplied for pathogenicity tests.

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Replicated trials were conducted during the summers of 1998 and 1999 at commercial orchards in South Carolina to determine the influence of ground application of a metalized, high density polyethylene reflective film on fruit red skin color and maturity of peach (Prunus persica) cultivars that historically have poor red coloration. At each site there were two experimental treatments: 1) control and 2) reflective film (film). Film was applied 2 to 4 weeks before anticipated first harvest date by laying a 150-cm (5-ft) wide strip of plastic on either side of the tree row in the middles. Treatment areas at a given farm ranged from 0.25 to 0.5 ha (0.5 to 1.0 acre) in size and each treatment was replicated four times at each site. At harvest, two 50-fruit samples were picked from each plot per treatment. All fruit were sized and visually sorted for color (1 = 0% to 25%, 2 = 26% to 50%, 3 = 51% to 75%, and 4 = 76% to 100% red surface, respectively). A 10-fruit subsample was selected following color sorting and evaluated for firmness and soluble solids concentration (SSC). All cultivars tested (`CVN1', `Loring', `Bounty', `Summer Gold', `Sunprince', `Cresthaven' and `Encore') experienced significant increases in percent red surface when film was used in 1998 and 1999. This color improvement ranged from 16% to 44% (mean = 28%). On average, fruit from film were 4.2 N (0.9 lb force) softer and had 0.3% higher SSC than control fruit. Growers harvested more fruit earlier and in fewer harvests for film. Fruit size was not affected by film. Reflected solar radiation from film was not different in quality than incident sunlight. Film resulted in an increase in canopy air temperature and a reduction in canopy relative humidity during daylight hours.

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Pawpaw (Asimina triloba) is a native North American tree that has potential as a new fruit crop or for use in landscapes, but until recently, little information has been available to nurseries on containerized production of this species. Pawpaw seedlings develop a strong taproot with a fragile root system, which can be easily damaged upon digging; therefore, most nurseries propagate trees in containers. Pawpaw seed requires stratification for optimal germination and seed is sensitive to desiccation. The seed also cannot tolerate freezing temperatures [<-15 °C (5.0 °F)]. A well-aerated potting substrate with a high sphagnum peat moss component (>75% by volume), cation exchange capacity, and water holding capacity can be used effectively in container production. Tall containers should be used to accommodate the developing taproot of seedlings. The slow-release fertilizer Osmocote 14-14-14 (14N-6.1P-11.6K) incorporated into Pro-Mix BX potting substrate can be used effectively as the sole fertilizer source at a treatment rate of 2.22 kg·m-3 (3.742 lb/yard3) in containerized pawpaw production. It can also be used at a lower rate of 0.81 kg·m-3 (1.365 lb/yard3) when supplemented with weekly applications of 500 mg·L-1 (ppm) of Peters 20-20-20 (20N-8.78P-16.6K) liquid-feed fertilizer. Bottom heating [32 °C (89.6 °F)] of container-grown pawpaw seedlings results in greater lateral and total root dry weight than in seedlings grown at ambient temperature [24 °C (75.2 °F)], which could increase the rate of establishment of seedlings in the field. Bottom heating of container-grown pawpaw seedlings could decrease both the time to produce a saleable plant and the cost of heating greenhouses. Growth of containerized pawpaw seedlings is enhanced by low to moderate shading with polypropylene shade fabric (28% or 51%) outdoors and low shading (33%) in the greenhouse, in a manner typical of that reported for other shade-preferring plants. Low to moderate shading of pawpaw seedlings grown outdoors greatly increases leaf number, total leaf area, and total plant dry weight compared to nonshaded seedlings, suggesting that commercial nurseries can improve production of containerized pawpaw seedlings using a shading regime outdoors.

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Thirty-four extant pawpaw [Asimina triloba (L.) Dunal] cultivars and advanced selections representing a large portion of the gene pool of cultivated pawpaws were investigated using 71 randomly amplified polymorphic DNA (RAPD) markers to establish genetic identities and evaluate genetic relatedness. All 34 cultivated pawpaws were uniquely identified by as few as 14 loci of eight primers. Genetic diversity of the existing gene pool of cultivated pawpaws, as estimated by Nei's gene diversity (He), was similar to that of wild pawpaw populations. The genetic relatedness among the cultivated pawpaws examined by UPGMA cluster analysis separated 34 cultivars and selections into two distinct clusters, a cluster of PPF (The PawPaw Foundation) selections and a cluster including a majority of the extant cultivars selected from the wild and their derived selections. The results are in general agreement with the known selection history and pedigree information available. The consensus fingerprint profile using the genetically defined RAPD markers is a useful and reliable method for establishing the genetic identities of the pawpaw cultivars and advanced selections. This also proved to be an improved discriminating tool over isozyme markers for the assessment of genetic diversity and relatedness. RAPD profiling of data presented in this study provides a useful reference for germplasm curators engaged in making decisions of sampling strategies, germplasm management and for breeders deciding which parents to select for future breeding efforts.

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