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  • Author or Editor: Stephen Leong x
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Gibberellic acid (GA3), a plant growth regulator used routinely in the production of seedless bunch grapes, was sprayed on the seeded muscadine grape cultivar Triumph. GA3 at 100, 200, and 300 mg·L-1 was sprayed on the leaves and fruit clusters at late bloom; a second spray followed 1 week later. The sprayed vines produced more than 20% seedless berries and the size of the berries with seeds increased significantly. GA3 application in commercial muscadine grape production may have potential benefits.

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Vitis shuttleworthii is one of the most disease and pest resistant grape species originated and distributed in the southeast United States. It is highly resistant to Pierce's disease, anthracnose, black rot and downy mildew diseases, which are the limited factors to grow Vitis vinifera grapes in this region. A V. shuttleworthii cDNA library was constructed with mRNA isolated from leaves and flowers harvested during anthesis. 12,008 clean EST sequences were obtained and assembled. and generated 5776 unigenes 2106 contigs and 3670 singletons). ESTs distribution based on protein function using a modified MIPS MATDB Arabidopsis Scheme revealed that 7% of the V. shuttleworthii ESTs were related to disease/pest defense or stress tolerance genes. Over 300 contigs containing complete or 90% open coding region of known functional genes were obtained. The ESTs that were annotated as pathogenesis-related proteins, enzymes in salicylic acid, jasmonic acid, and ethylene signaling, were selected for further study in order to elucidate the role and interaction of them in the signal transduction cascade that leads to grape defense gene activation upon treatment of bacterial pathogen. We report the identification of novel disease resistant genes based on preliminary pathogenesis-relative pathways network analysis.

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Muscadine grapes (Vitis rotundifolia Michx.), native to the southeastern United States, have a distinct flavor, and grocers are interested in marketing them as table grapes. Two studies using 'Fry' muscadines were conducted to assist the muscadine industry in providing quality table grapes. Study 1 (1998 and 1999) evaluated density sorting and relationships between maturity, color, soluble solids, firmness, shelf life, and sensory evaluation of grapes. Study 2 (1998) determined the effect of storage on quality attributes of different maturities of grapes and evaluated use of polyethylene bags to extend their storage. Density separation successfully sorted grapes by maturity. Muscadine berry color may allow for visual or electronic sorting to eliminate immature fruit. Sensory panelists could distinguish differences in maturities for all sensory attributes. In 1999 maturities 3 and 4 (≈24-33 soluble solids: acid ratio) were preferred overall by panelists. As maturity increased, soluble solids and pH increased, and acidity decreased. Firmness decreased as maturity and storage at 2 °C increased. Percent decay increased with maturity and storage time. Grapes stored in polyethylene bags had reduced decay. A chart developed from the 1999 data related berry color to soluble solids: acid ratio, soluble solids, tartaric acid, and pH. Data from these studies can be used by industry to establish harvest parameters and enhance marketability of 'Fry' muscadine grapes.

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Papaya seedlings segregate for sex expression as females or hermaphrodites. Typically only hermaphrodite fruit are marketed in Hawaii. The agronomic practice of growing multiple seedlings that are later thinned to a single hermaphrodite tree is wasteful of seed, labor, and resources, especially when seed is costly. We compared growth of plants propagated by the clonal methods of micropropagation or rooting vegetative cuttings versus plants initiated as seedlings and transplanted. The seedlings were either single-planted hermaphrodites as identified by the polymerase chain reaction (PCR) or multiple-planted, thinned seedlings. The experiments were carried out in three different locations on two islands in Hawaii. Clonally propagated plants were significantly shorter than seedlings and bore flowers earlier and lower on the trunk at all locations. Stem diameter differences were not significant even though plant size was different at planting time. Percentage of trees in bud varied significantly in the third month after transplanting when about 90% of the rooted cuttings and large micropropagated plants had formed flower buds while only one multiple-planted seedling developed a bud. Overall, the clonally propagated plants were more vigorous and earlier bearing than were the seedling plants. There is good potential for adoption of clonal propagation when production becomes efficient enough to compete in price with the current practice of over planting and thinning.

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Gynodioecious papaya (Carica papaya L.) seedlings in commercial cropping systems in Hawaii are typically multiple-planted and thinned upon flowering to a single hermaphrodite because seedlings segregate for sex expression. Use of clonally propagated hermaphrodites would eliminate the over-planting practice and may provide other advantages. Yields of clonally propagated hermaphrodites were compared with single- and multiple-planted seedlings in three fields on two islands in Hawaii. Cloned hermaphrodites were either rooted cuttings or in vitro micropropagated plants. Clonally propagated plants bore ripe fruit 1 to 3 months earlier than thinned seedlings and had significantly higher early and cumulative yields. At each site, cumulative yields of thinned seedlings never reached the same level as those of clonally propagated plants. The yield benefit from clonally propagated plants was greatest at Keaau, the lowest sunlight and least productive test site.

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