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Volume 44 (2009): Issue 5 (Aug 2009) x
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Allen V. Barker

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Thomas Sotiropoulos, Georgios Syrgianidis and Nikolaos Koutinas

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Richard A. Criley

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Gerry Henry Neilsen, Denise Neilsen and Linda Herbert

A randomized complete block, split-plot experiment with six replicates was established and maintained for the first six fruiting seasons (1999 to 2004) in a high-density apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] orchard on M.9 rootstock planted in Apr. 1998. This report assesses responses to six main-plot fertigation treatments, each containing three tree subplots of five different cultivars (Ambrosia, Cameo, Fuji, Gala, and Silken). Fertigation treatments were a factorial combination of two nitrogen (N) rates and three N application timings. N was applied at low (28 mg N/L) or high (168 mg N/L) concentrations daily at 0 to 4, 4 to 8, or 8 to 12 weeks after full bloom (wafb). Under greater N inputs, all cultivars had increased midsummer leaf and harvested fruit N concentrations, decreased fruit firmness, and in heavy crop years, decreased percent red color. Annual yield of all cultivars was significantly increased by N rate in a single year, but their cumulative yields were not different between treatments as a result of rate or timing. Altering the timing of N application within 12 wafb only affected leaf and fruit tissue N concentration. Leaf N was higher after 4 weeks of fertigation any time, although concentrations declined over the growing season, reaching minimum values around harvest. Fruit N was increased by fertigation 4 to 12 wafb. Yield, fruit firmness, and color were unaffected by fertigation timing. Critical fruit quality issues for ‘Gala’ and ‘Silken’ were small fruit size, for Ambrosia low fruit numbers, and for ‘Cameo’ soft fruit. ‘Fuji’, which achieved high yield and leaf N concentration and firm fruit, had poor red color regardless of N treatments.

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Sadanand A. Dhekney, Zhijian T. Li, Michael E. Compton and Dennis J. Gray

Stamens and pistils from mature grapevines and leaves from in vitro micropropagation cultures were used to optimize parameters influencing somatic embryogenesis in Vitis. Embryogenic competence was dependent on species/variety, explant type and developmental stage, medium composition, and growth regulator concentration. Of varieties evaluated, a greater number produced embryogenic cultures from stamens and pistils (26) compared with leaves (six). Among the different stamen and pistil stages, Stage II and III explants produced the maximum embryogenic response regardless of genotype and medium composition. Of seven culture media tested, the highest embryogenic response was recorded from varieties cultured on MSI (18) and PIV (16) media. Experiments annually repeated over 3 to 10 years demonstrated reproducible results. Highly reliable protocols for somatic embryogenesis were obtained for 29 Vitis species and varieties, including 18 Vitis vinifera varieties, Vitis riparia, Vitis rupestris, Vitis champinii, and eight Vitis hybrids. Embryogenic cultures were maintained on X6 medium for a period of 6 months to 2 years depending on the variety and used in studies involving genetic transformation and transgenic plant regeneration.

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Michael Mazourek, George Moriarty, Michael Glos, Maryann Fink, Mary Kreitinger, Elizabeth Henderson, Greg Palmer, Ammie Chickering, Danya L. Rumore, Deborah Kean, James R. Myers, John F. Murphy, Chad Kramer and Molly Jahn

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Gayle M. Volk and David Stern

Garlic (Allium sativum L.) cultivars grown under diverse conditions have highly elastic environmental responses, particularly relating to skin color and yield. Ten diverse garlic cultivars were grown at 12 locations in the United States and Canada for 2 consecutive years to identify the environmentally responsive phenotypic traits of garlic. Clove arrangement, number of topsets, topset size, topset color, number of cloves, clove weight, clove skin color, and clove skin tightness were generally stable for each cultivar regardless of production location and conditions. Scape presence varied with cultivar and location, but for the most part, cultivars classified as hardneck types produced scapes and those classified as softnecks did not produce scapes. Bulbs grown at the northern Colorado, Minnesota, Pennsylvania, Vermont, and Washington locations were generally larger than the other locations. Soil potassium levels were positively correlated with bulb circumference and fresh weight. Soil sulfur and manganese levels were correlated with bulb sulfur and manganese content. Bulb wrapper color and intensity were highly dependent on location and cultivar. The Silverwhite cultivar was consistently white and ‘Ajo Rojo’, ‘German White’, ‘Inchelium’, ‘Sakura’, and ‘Spanish Roja’ were generally white with some faint violet or brown stripes or splotches across the locations. In contrast, cultivars Chesnok Red, Purple Glazer, Red Janice, and Siberian were more likely to have moderate or dark violet stripes, streaks, or splotches, particularly when grown at the northern Colorado, Minnesota, Nevada, New York, Ontario, Pennsylvania, or Washington locations. These results can help farmers identify niche regional markets that provide novel products to consumers. From these results, it was shown that garlic cultivars or classes grown under diverse conditions have highly elastic soil nutrient responses, particularly relating to skin color and yield.

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Ana Fita, Belén Picó, Rita C.S. Dias and Fernando Nuez

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Raquel González-Herranz, Kimberley A. Cathline, Matthew W. Fidelibus and Jacqueline K. Burns

The application of methyl jasmonate (MeJA) to grapes (Vitis vinifera L.) may decrease fruit detachment force (FDF) and promote the development of dry stem scars on the berries, both of which could improve the quality of machine-harvested raisin grapes. However, treatment with MeJA also promotes preharvest fruit drop, which is undesirable. Thus, experiments were conducted to determine how the concentration of MeJA applied and time after treatment affect FDF and abscission of grapes. Mature ‘Thompson Seedless’ grapevines were treated with one of five different solutions containing 0, 0.2, 2, 10, or 20 mm MeJA, and FDF and fruit abscission were monitored for ≈2 weeks. Treatment with 2 mm or less MeJA had inconsistent effects on FDF and did not promote abscission, whereas treatment with 10 to 20 mm MeJA reduced FDF within 2 to 3 days after treatment (DAT) and promoted abscission, which began on ≈3 DAT and persisted for ≈8 DAT. Thus, to optimize the use of MeJA as a harvest aid for ‘Thompson Seedless’ may require application of between 2 and 10 mm MeJA followed by harvest within 3 DAT.

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Martín Mata-Rosas and Víctor M. Salazar-Rojas

Protocols for in vitro propagation from protocorms of Mormodes tuxtlensis Salazar, Cuitlauzina pendula La Llave & Lex., and Lycaste skinneri (Batem. Ex. Lind.) Lind., three endangered species distributed in Mexico and highly appreciated as ornamentals, were developed. The effect of two different culture media, Murashige and Skoog (MS) and modified Knudson (KCm), combined with varying concentrations of N6-benzyladenine (0, 2.2, 4.4, 8.9, and 13.3 μM) and α-naphthaleneacetic acid (0, 0.5 and 2.7 μM), were investigated. Shoot formation and development of protocorm-like bodies were observed. For all three species, cultures in MS produced more shoots per explant than those in KCm, and those shoots were longer and more robust in appearance. Maximum number of shoots for M. tuxtlensis (1.5) and C. pendula (24.3) were obtained in media supplemented with 13.3 μM and 2.2 μM N6-benzyladenine, respectively. Conversely, for L. skinneri the greatest shoot production (16.4) was achieved in medium supplemented with 2.7 μM α-naphthaleneacetic acid. Subculturing explants in MS basal medium allowed further development and rooting of the shoots as well as growth of protocorm-like bodies. The effect of different potting mixes on ex vitro survival plantlets was also investigated; pine bark:oak charcoal:pumice (3:1:1) allowed the highest survival rates in all three species.