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  • Author or Editor: C.M. Thompson x
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Prevention of the introduction of bacterial fruit blotch of watermelon, caused by Acidovorax avenae subsp. citrulli, into the transplant house or field is the most effective control strategy. Watermelon seedlots currently are screened for A. avenae subsp. citrulli, but other cucurbits, often grown in the same transplant house or field, generally are not as carefully monitored. In 1997 and 1999 field tests, cultivars of watermelon, muskmelon, honeydew melons, acorn squash, butternut squash, yellow squash, zucchini squash, cucumber, and pumpkin were evaluated for foliar and fruit susceptibility to bacterial fruit blotch and for seed transmission of A. avenae subsp. citrulli. The bacterium was introduced into the field on infected watermelon transplants or by misting a bacterial suspension onto fruit of the cucurbits. Foliar and fruit symptoms were more extensive in the watermelon, muskmelon, and honeydew melons than in the other cucurbits. In greenhouse grow-out assays, seed transmission of A. avenae subsp. citrulli was detected in every cucurbit in at least one of the two seasons, even though there were no fruit symptoms in some of them. Thus, any cucurbit crop plant should be considered a potential source for the introduction of A. avenae subsp. citrulli into the transplant house or field.

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Abstract

The accumulation of Pierce’s disease bacterial occlusions in xylem vessels of leaves of susceptible ‘Schuyler’ bunch grapes occurred 2 months earlier than the accumulation in leaf vessels of the more tolerant ‘Carlos’ and ‘Welder’ muscadines. The first appearance of leaf marginal necrosis symptoms occurred when the accumulation of bacterial occlusions was approaching the maximum—the last week of June in the bunch grape, the last week of Aug. in the 2 muscadines. The site of bacterial accumulation was primarily in the leaves of ‘Carlos’, but in both leaves and stems of ‘Schuyler’ and ‘Welder’. Stem dieback symptoms are more common in the latter 2 cultivars.

Open Access

Abstract

Aluminum concentrations of 0, 3, 10, 30, and 100 ppm in nutrient solution reduced proportionately the dry weights of stem, roots, and leaves of seedlings of ‘Lovell’ peach [Prunus persica (L.) Batsch]. Roots grown at 30 and 100 ppm A1 were shorter, thicker, and had less branching than roots grown at lower concentrations. The epidermal and endodermal cells were small, with grossly thickened cell walls. Cells of the cortex were shortened in the longitudinal axes. Leaf A1 level indicated solution A1 better than did the A1 levels of roots, stems, or the 2% acetic acid-extractable A1 fraction of leaves, stems, or roots. The concentration of Ca, Mg, Mn, and P were reduced as A1 concentration increased.

Open Access

Seedlings of 22 watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] cultivars and two plant introductions were screened in the greenhouse for resistance to the fruit blotch bacterium. There were significant differences in disease severity among cultivars, but no cultivar was immune to the bacterium. In field tests, fruit of 18 commercial cultivars were inoculated individually or became infected naturally from diseased foliage. Cultivars with relatively resistant fruit included `Sugar Baby', `Jubilation', `Mirage', `Calsweet', `Crimson Sweet', `Royal Sweet', and `Sangria'. The more susceptible cultivars generally had a light-colored rind. Cultivar level of resistance to bacterial fruit blotch may not be sufficient under conditions conducive to severe disease development.

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Three-year-old `Valencia' orange [Citrus sinensis (L.) Osbeck] trees were exposed to air pollutants for 4. years in open-top field chambers to determine the chronic effects of ambient oxidants (primarily ozone) or sulfur dioxide (SO2) on fruit yield and quality and tree growth. Ozone concentrations averaged 0.012,0.040, and 0.075 ppm for 0800 to 2000 hr during April to October for filtered, half-ambient, and full ambient oxidant chambers. Sulfur dioxide was applied continuously at 0.09 ppm. Oxidant and SO2 effects were only marginally significant, as there was considerable variability in response among individual trees and between years. Across two “on” production years, yields were 31% lower with ambient oxidants, 11% lower with half-ambient oxidants, and 29% lower with sulfur dioxide compared to filtered air. Number of fruit per tree was reduced by ambient oxidants and SO2. Individual fruit weights were reduced by ambient oxidants, but no other fruit quality characteristics showed definite responses to ambient oxidants or SO2. Ambient oxidants had no effect on yield or quality of fruit during one “off' production year. Neither ambient oxidants nor SO, affected tree growth.

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