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Cecilia E. McGregor, Douglas W. Miano, Don R. LaBonte, Mary Hoy, Chris A. Clark, and Guilherme J.M. Rosa

%) takes place in developing countries where it is mainly grown by small/subsistence farmers. Stem cuttings provide a convenient way to propagate sweetpotato, but also contribute to the spread of diseases ( Clark et al., 1997 ; Salazar and Fuentes, 2000

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Gregory M. Peck, Candace N. DeLong, Leon D. Combs, and Keith S. Yoder

immense insect, disease, and weed pressure experienced in this region ( Cromwell et al., 2011 ; Peck et al., 2010 ; Williams et al., 2016 ). Additionally, crop load management options are limited in organic production because the USDA-NOP prohibits the

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Beth Clendenen, B.K. Behe, and K.L. Bowen

Eleven rose cultivars were field planted and evaluated weekly for disease, defoliation, and overall vigor in order to compare natural resistance to blackspot (Diplocarpon rosae). Alternative treatments were also compared for efficacy in low-maintenance disease control. Treatments included a bimonthly application of chlorothalonil, a bimonthly application of a horticultural oil, an application of chlorothalonil based on rain events, and a no-treatment control. Cultivars showed significant differences in disease severity, defoliation, and overall performance, with old garden rose varieties showing more natural disease resistance than modern susceptible varieties included in the study. Chlorothalonil applied on a 14-day spray schedule did provide a significant decrease in blackspot disease severity when compared to other treatments. A significant incidence of secondary disease including Cercospora rosicola and Botrytis cinerea occurred on old garden rose varieties. No treatment differences were found for these diseases. `Belinda's Dream', `The Fairy', and `Red Mediland' ranked highest in overall performance throughout the season.

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T.E. Morelock, J.C. Correll, and L.P. Brandenberger

Downy mildew (Blue mold) is probably the most common spinach disease in most parts of the world, and it can be a problem in the mid-South. Frequently, other diseases such as white rust and fusarium cause major crop loss. The Arkansas breeding program was initiated 25 years ago to address white rust and fusarium, as well as other diseases that destroy spinach crops. Since single gene resistance is not available for most spinach diseases, it was necessary to utilize polygenic resistance to develop varieties that are resistant to most of the common spinach diseases that occur in the Arkansas River Valley of Arkansas and Oklahoma. Highly resistant genotypes have been developed by using disease nurseries and field screening, so frequent selections are made based on the reaction to 3-4 diseases.

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Danny L. Barney, Michael Bauer, and Jennifer Jensen

the trials produced a low percentage of marketable Christmas trees after 10 years. Our objectives were to compare survival, frost susceptibility, growth rates, total growth, tree shapes, disease resistance, and suitability for landscape and Christmas

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Akhtar Ali and James R. Baggett

The inheritance in corn (Zea mays L.) of resistance to head smut disease incited by Sphacelotheca reiliana (Kuhn) Clinton was studied in the field on crosses of resistant dent corn line N6 with two susceptible sweet corn (su1) inbred lines. Disease incidence in the resistant parent (Pr) was 0% to 4%, and 83% to 96% in the susceptible parent (Ps). Predisposition of seedlings by clipping just above ground level increased percent infected in progeny populations by as much as 4-fold, but did not affect disease incidence in the, parents. At the lower disease incidence of unclipped plots, the F1, F2, and BCr means were close to the mean of Pr, suggesting dominance of resistance. At the high disease incidence of clipped plots, the relationship of parent and progeny means “suggested additive inheritance. Epistasis was also generally present with a higher level indicated for unclipped plots. Inheritance was concluded to be quantitative. Reciprocal differences were observed only in backcrosses. In the F2 and BCs populations, plants grown from dent (Su1) seed were lower in disease incidence than plants grown from su1 seed.

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A. Gera, L. Maslenin, A. Rosner, M. Zeidan, S. Pivonia, and P.G. Weintraub

Yellows diseases in ornamental crops have become more common in Israel, and phytoplasmas have been detected in several crops. Recently, symptoms typical of a phytoplasma infection were observed on a large number of Limonium hybrids grown in commercial fields in Israel. Examination of samples from diseased plants by electron microscopy revealed the presence of pleiomorphic membrane-bound bodies in the phloem cells. Diseased plants were additionally analyzed by PCR using universal and nested primers and revealed upon sequencing products of 1143, 788 and 722 bp (Li-IL, Li-b2-IL, Li-v3-IL, respectively). Analysis of the PCR products, associated with infected Limonium, clustered within two major groups of phytoplasmas (16SrV and 16SrIX), elm yellows and almond witches broom. This is the first published record of these phytoplasmas in Israel.

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J.M. Sherman, K.S. Reddy, S.E. Newman, and J.A. Spencer

Most modern roses are highly susceptible to the disease blackspot caused by the fungus Diplocarpon rosae. This contrasts to species roses that are resistant to the disease. To gain information on the biochemical factors in this resistance mechanism, we are studying the involvement of proteins. Soluble proteins of modern roses and species roses were extracted and analyzed by SDS-PAGE. When healthy leaves were examined, there were no distinct differences in the protein patterns, indicating that there are no constitutive proteins involved in the disease resistance mechanism. There were no differences between healthy and infected leaves of resistant genotypes. When detached leaves of some susceptible types were infected with the fungus new proteins seemed to appear in the healthy region surrounding the blackspot lesion. These proteins may be involved in resisting the spread of the pathogen.

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George H. Clough and Philip B. Hamm

Three transgenic yellow crookneck squash (Cucurbita pepo var. melopepo) and five transgenic cantaloupe (Cucumis melo, Reticulatus group) lines were field-tested in 1993 and 1994, respectively, for resistance to Zucchini Yellow Mosaic Virus and Watermelon Mosaic Virus II. During both years, non-transgenic plants were inoculated with virus before transplanting to provide a high virus threat to the transgenic plants. Before and after transplanting, serological (ELISA) testing was used to obtain baseline information on transformed plants and to confirm field virus infection. In both years, plant disease development was rated weekly; yield was assessed during 1993. Disease progression, yield, and end-of-season ELISA indicated a significant reduction in frequency of disease incidence in the transgenic lines. Total squash yields did not differ between the transformed and unchanged lines, but the transgenic lines yielded more marketable fruit than the non-transgenic line.

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Yan Chen, Regina Bracy, and Allen Owings

Annual vinca, Catharanthus roseus, is exceptionally adaptive to the summer heat and the sandy loam or clay soil in the southeastern region and provides season-long blooms once established in landscape plantings. A wide variety of colors, sizes, and applications are available for landscape use. However, diseases such as alternaria leaf spot and phytophthora leaf blight are prevalent in this region in vinca plantings. Effective disease control requires frequent fungicide application that is expensive and may pose negative effects on the environment. Proper planting techniques including date of planting, fertilization rate at planting, and variety selection may improve plant growth, reduce disease severity, and save landscape service business labor in disease management. Plants of three varieties: open-pollinated `Cooler Hot Rose', F1 hybrid `Titan Rose', and trailing variety `Mediterranean Lilac' were planted on 1 Apr. or 1 May in landscape plots. Plants were at the same growth stage at the time of planting and were fertilized with Osmocote 14–14–14 (3 months) at 0, 35, 70, or 140 g·m2. Plant growth index indicates that plant growth increased significantly at increasing fertilization rates; however, plant overall quality ratings were not significantly different among fertilized plants. Disease incidence in July suggests that late planting may reduce alternaria leaf spot in open-pollinated and hybrid upright type vinca. Disease severity in August was more pronounced on trailing vinca and more severe when plants were not fertilized or fertilized with the highest fertilization rate. Tissue analysis indicates that trailing vinca `Mediterranean Lilac' may require less fertilization than upright type.