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  • Author or Editor: J.W. Harris x
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Screening for resistance to Elsinoe ampelina (de Bary) Shear, causal agent of grape anthracnose, in grapevine seedlings is commonly conducted by natural infection over 3 to 4 years in the vineyard. The objective of this research was to develop a greenhouse screening method for selecting grapevine seedlings with resistance to anthracnose. Spores of E. ampelina were obtained from 3- to 4-week-old cultures on potato dextrose agar. Inoculum concentrations ranging from 1.3 × 103 to 1.3 × 107 E. ampelina conidia per mL were evaluated and 106 conidia/mL was optimum. The time of incubation of seedlings in a moist chamber after inoculation varied from 24 to 120 hours with 24 to 72 hours resulting in good symptom development. Temperatures in the moist chamber from 16 to 32 °C were evaluated and the most consistent results were obtained at 20 to 28 °C. The most effective method for selecting anthracnose-resistant grape seedlings in the two-to-three true-leaf stage was misting the seedlings with a suspension containing 106 conidia/mL in water and placing the inoculated seedlings in a moist chamber at 24 °C for 48 hours, followed by 8 days on a greenhouse bench. Resistant seedlings from the greenhouse screening (those with <10 foliar lesions) were transplanted into the vineyard and found to be resistant to anthracnose infection under rainy, humid conditions. This greenhouse procedure for selecting grapevine cultivars and breeding lines with resistance to anthracnose is accurate, economical, and labor-saving.

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Ploidy of in vitro watermelon plantlets was estimated by painting the lower epidermis of leaves with fluorescein diacetate (FDA) and observing fluorescence of guard cell chloroplasts with a microscope and UV light. Leaves from shoot-tip cultures of known diploid and tetraploid cultivars were used to establish the mean number of chloroplasts per guard cell pair for in vitro plantlets. Leaves from diploid and tetraploid plantlets had 9.7 and 17.8 chloroplasts per guard cell pair, respectively. This method was used to estimate ploidy of shoots regenerated from cotyledon explants of the diploid cultivar Minilee. Approximately 10.6% of regenerated shoots were classified as tetraploid while still in vitro. Putative tetraploids were transplanted to the field and self-pollinated. A majority of polyploids identified in vitro were true breeding, nonchimeric tetraploids. This study demonstrate that FDA can be used to estimate ploidy of in vitro shoots of watermelon prior to acclimatization and transfer of plants to the greenhouse or field.

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Abstract

A procedure and device is described involving a small jet of water under pressure directed onto the surface of a sweetpotato (Ipomoea batatas L.) root. The time required for the stream to abrade the skin is taken as a measure of the “skin-toughness.” The time required for abrasion of 18 cultivars was correlated with their condition scores after mechanical harvesting. Skin was more resistant to abrasion 1 day after digging than when freshly dug and curing further increased skin-toughness. Relative skin-toughness of cultivars changes during curing and storage.

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The effects of supplemental Ca on salinity tolerance were tested using a Brassica rapa L. landrace, `Sani', which is salt-sensitive. Plants were grown in a continuous aerated hydroponic system with 0.25-strength Hoagland solutions containing 125 mM NaCl plus 0, 2.5, 5.0 or 10 mM CaCl 2. The effects of Ca treatment were significant in reducing Na accumulation in roots, Na+ transport from roots to shoots and in enhancing K and Ca accumulation and transport. The Ca addition also enhanced the selectivities of both K and Ca over Na of accumulation at roots and of transport to shoots. However, supplemental Ca did not alleviate the growth reduction caused by the NaCl salinity. These results suggest that the growth inhibition of salt-treated B. rapa `Sani' is mainly caused by factors other than Na, K, and Ca contents in plants.

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Bifenthrin and fipronil are important pesticides used in the nursery industry for the control of imported fire ants. Our research measured the influence of irrigation frequency and time on the degradation of bifenthrin and fipronil in pine bark nursery medium. Pine bark media leachates were collected over a 180-d period. Levels of bifenthrin, fipronil, and metabolites of fipronil (MB 46513, MB 45950, MB 46136) were measured using gas chromatography and mass spectrophotometery. Bifenthrin leachate concentrations decreased from 60 ppb on day 1 to ≈1 ppb after 120 d. Fipronil leachate concentrations decreased from 40 ppb on day one to a low of 15 ppb after 120 d. In contrast, metabolites MB 45950 and MB 46136 gradually increased over the 180-d period. Metabolite MB 46513 was not detected during the experiment. Pine bark medium leachate concentrations of bifenthrin and fipronil were greater than previously reported levels in pure water. We theorize that organic compounds present in pine bark may have increased the solubility of these chemicals.

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Long-established native tree populations reflect local adaptations. Representation of diverse populations in accessible ex situ collections that link information on phenotypic expression to information on spatial and temporal origination is the most efficient means of preserving and exploring genetic diversity, which is the foundation of breeding and crop improvement. Throughout North America, sympatric Carya species sharing the same ploidy level tend to hybridize, permitting gene flow that contributes to regional diversity and adaptation. The topographic isolation of many fragmented populations, some of which are small, places native Carya populations of United States, Mexico, and Asia in a vulnerable position and justifies systematic collection and characterization. The characterization of indigenous Mexican pecan and other Carya populations will facilitate use for rootstocks and scion breeding and will contribute to pecan culture. The Asian species, as a group, are not only geographically isolated from North American species, but also occur in disjunct, fragmented populations isolated from other Asian species. Section Sinocarya includes the members of the genus most vulnerable to genetic loss. With all species, recognition of utility based on characterization of ex situ collections may contribute to the establishment of in situ reserves. Global Carya genetic resources should be cooperatively collected, maintained, characterized, and developed. The integration of crop wild relatives into characterization and breeding efforts represents a challenging opportunity for both domestic and international cooperation. Genomic tools used on the accessible collections of the National Collection of Genetic Resources for Pecans and Hickories (NCGR-Carya) offer great potential to elucidate genetic adaptation in relation to geographic distribution. The greatest progress will be made by integrating the disciplines of genetics, botany, pathology, entomology, ecology, and horticulture into internationally cooperative efforts. International germplasm exchange is becoming increasingly complicated by a combination of protectionist policies and legitimate phytosanitary concerns. Cooperative international evaluation of in situ autochthonous germplasm provides a valuable safeguard to unintended pathogen exchange associated with certain forms of germplasm distribution, while enabling beneficial communal exploration and directed exchange. This is threatened by the “proprietary” focus on intellectual property. The greatest risk to the productive development of the pecan industry might well be a myopic focus on pecan production through the lens of past practice. The greatest limitation to pecan culture in the western United States is reduced water quantity and quality; in the eastern United States the challenge is disease susceptibility; and insufficient cold hardiness in the northern United States. The greatest benefit for the entire industry might be achieved by tree size reduction through both improved rootstocks and scions, which will improve both nut production and tree management, impacting all areas of culture. This achievement will likely necessitate incorporation of crop wild relatives in breeding, broad cooperation in the testing leading to selection, and development of improved methods linking phenotypic expression to genomic characterization. The development of a database to appropriately house information available to a diverse research community will facilitate cooperative research. The acquisition of funds to pursue development of those tools will require the support of the pecan industry, which in the United States, is regionally fragmented and focused on marketing rather than crop development.

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The objectives of this study were to determine root and shoot growth periodicity for established Fraxinus pennsylvanica Marsh. (green ash), Quercus coccinea Muenchh. (scarlet oak), Corylus colurna L. (Turkish hazelnut), and Syringa reticulata (Blume) Hara `Ivory Silk' (tree lilac) trees and to evaluate three methods of root growth periodicity measurement. Two methods were evaluated using a rhizotron. One method measured the extension rate (RE) ofindividual roots, and the second method measured change in root length (RL) against an observation grid. A third method, using periodic counts of new roots present on minirhizotrons (MR), was also evaluated. RE showed the least variability among individual trees. Shoot growth began before or simultaneously with the beginning of root growth for all species with all root growth measurement methods. All species had concurrent shoot and root growth, and no distinct alternating growth patterns were evident when root growth was measured by RE. Alternating root and shoot growth was evident, however, when root growth was measured by RL and MR. RE measured extension rate of larger diameter lateral roots, RL measured increase in root length of all diameter lateral roots and MR measured new root count of all sizes of lateral and vertical roots. Root growth periodicity patterns differed with the measurement method and the types of roots measured.

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