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Sarah E. Dixon, Jerri L. Henry, Dean S. Volenberg, and Reid J. Smeda

agricultural commodity, with more than 5.4 million acres planted in 2020 ( U.S. Department of Agriculture, National Agricultural Statistics Service, 2020 ). The proximity of DT soybean to sensitive crops such as grapes ( Vitis sp.) can be problematic when

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Derek W. Barchenger, John R. Clark, Renee T. Threlfall, Luke R. Howard, and Cindi R. Brownmiller

Muscadine grapes ( Vitis rotundifolia Michx.) are relatively insect- and disease-resistant native plants and are commonly grown in the southeastern United States to diversify farm operations ( Conner, 2009 ; Silva et al., 1994 ; Striegler et al

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Ashley Basinger and Richard Durham

Current propagation techniques for grapevine rootstocks involve rooting cuttings from dormant or actively growing canes and require relatively large amounts of propagation wood. We report an alternative method involving high-frequency, in vitro rooting of single-node cuttings that can be used when limited amounts of plant material are available. Propagation material was taken from greenhouse-grown plants of Vitis arizonica, V. treleasei, and V. treleasei interspecific hybrids (with V. acerifolia, V. arizonica, and/or V. doaniana) collected from the wild in New Mexico. Shoots were cut into one-node sections and surface sterilized in 25% commercial bleach for 10 minutes followed by three rinses in sterile water. The cuttings were placed on media containing half-strength Murashige and Skoog (MS) salts, MS vitamins, 20 g·L-1 sucrose, 2 g·L-1 phytagel, pH 5.8. The cuttings were incubated at 27 °C under a 16-hour photoperiod. Vitis vinifera `Cabernet Sauvignon' and `Chardonnay' were also rooted under similar conditions. All genotypes investigated rooted, but with varying frequency. Particular selections from the genotypes collected from the wild rooted at high frequency (>84% of cuttings rooted), while 66% of `Cabernet Sauvignon' and `Chardonnay' cuttings rooted. Plants were successfully established in the greenhouse. In vitro rooting of single-node cuttings appears to be a valid alternative for grapevine propagation.

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James R. McFerson, Warren F. Lamboy, and Steve Kresovich

We discuss a series of studies in our units employing molecular genetic markers in collection management, primarily for identity and diversity assessment and partitioning of genetic variation. Isozymes, random amplified polymorphic DNAs (RAPDs), and simple sequence repeat DNAs (SSRs) have been used for these purposes. We analyzed a range of Brassica oleracea accessions at six isozyme loci. Unique isozyme profiles (or fingerprints) were found for 40% of the individual genotypes within accessions. While isozymes were extremely valuable for partitioning genetic variability between and among subspecies, they failed to identify accessions and subspecies. Furthermore, relationships found did not correspond to those predicted by taxonomy. In a study of three species of Chinese vegetable brassicas using 112 RAPD markers, we were able to unambiguously distinguish all 52 accessions studied, despite some intra-accession variability. In addition, cluster analysis correctly grouped all individuals of the same species, but below that rank, taxonomic groupings occasionally broke down. RAPD profiles were found that unambiguously distinguished the three Brassica species from one another, but, for subspecies, no such profiles were found. In another RAPD study of B. oleracea subsp. capitata (cabbage), a closely related set of cultivars were not distinguishable, although more distantly related cultivars were. We had disappointing results with a RAPD study of Vitis accessions. DNA was extracted from the leaves of 23 greenhouse-grown and 52 field-grown vines. Twelve of the 23 greenhouse vines were rooted cuttings collected from 12 of the field-grown vines. Unfortunately, the RAPD profiles of all vines grown in the same location (whether greenhouse or vineyard) were more similar to one another than were profiles from the same clone grown in the two different locations. We are studying whether this result is due to physiological differences in plants growing under different conditions, to differences between PCR reagent lots, to pathogen infestation, or to DNA sample contamination. In a study of 23 accessions representing 15 Vitis species and three species hybrids, we used six different SSR markers to identify individual genotypes. We were able to unambiguously distinguish all genotypes, except two that were identical at all six loci. Review of planting records revealed that the two genotypes were probably the same grape clone. SSR results were not congruent with known taxonomic relationships or geographic origin of genotypes. The SSR polymorphisms found in even this small subset of the Vitis collection in principle make possible the identification of more than 130 trillion different genotypes. This high level of polymorphism, however, makes our particular SSR loci of limited use for identification of species and for the determination of genetic relationships. Molecular genetic markers offer a powerful, efficient approach to assessing questions of identity, relationship, and diversity in germplasm collections, but markers need to be selected based on their suitability for the particular task.

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Wanmei Jin, Jing Dong, Yuanlei Hu, Zhongping Lin, Xuefeng Xu, and Zhenhai Han

a widely grown fruit crop in the world. ‘Centennial Seedless’ of Vitis vinifera L. is one of the most widely grown grape varieties in China because it is suitable for both table consumption and wine production ( Kong, 2004 ). The berries of the

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Renata Koyama, Adriane Marinho de Assis, Lilian Yukari Yamamoto, Wellington Fernando Borges, Rogério de Sá Borges, Sandra Helena Prudêncio, and Sergio Ruffo Roberto

American grapes are widely cultivated in some areas of the world such as Brazil and the United States, mainly for grape juice production as well as for the fresh market. ‘Isabel’, syn. ‘Isabella’, grape ( Vitis labrusca L.) is one of the most

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David W. Ramming, Richard L. Emershad, and Ronald Tarailo

Hybridizations between seedless Vitis vinifera L. genotypes and V. rotundifolia (Michx.) were made specifically to introgress the seedless trait into the disease-resistant background of V. rotundifolia. The seedless, gynoecious P79-101 was hybridized with three V. rotundifolia parents, producing a total of 102 ovules. From these ovules, 44 embryos developed, producing 20 plants. Isozyme analyses and morphological traits confirmed that 19 of the plants were hybrids. Sixteen were planted in an experimental vineyard at California State Univ. Fresno. One seedling, C41-5, produced seedless fruit that appeared to be stenospermocarpic based on fruit and aborted seed size. Fruit weight was slightly less than that of `Thompson Seedless' (stenospermocarpic) and at least twice that of parthenocarpic fruit of `Black Corinth' and C41-7, a seeded hybrid with many parthenocarpic fruit. Aborted seeds of C41-5 were larger than, but not significantly different from, those of `Thompson Seedless', while parthenocarpic fruit from `Black Corinth' and C41-7 had aborted seeds that were smaller than those of C41-5. Seed weight of C41-7 averaged almost 10 times that of aborted C41-5 seeds. This is the first report of a stenospermocarpic, seedless hybrid of V. vinifera × V. rotundifolia.

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Derek W. Barchenger, John R. Clark, Renee T. Threlfall, Luke R. Howard, and Cindi R. Brownmiller

Native to the southeastern United States, the muscadine grape ( Vitis rotundifolia Michx.) is commonly grown for its unique flavor, high nutraceutical content, and pest and disease resistance, which is often a limiting factor in the production of

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A.G. Reynolds, D.A. Wardle, C. Zurowski, and N.E. Looney

One of three levels (O, 1, 10 mg·liter-1) of the cytokinin-active substituted phenylurea compound CPPU was applied with or without 100 mg GA/liter to developing clusters of `Sovereign Coronation' and Summerland Selection 495 grapes (Vitis spp.). In a similar experiment, one of three levels (0, 1, 10 mg·liter-) of either CPPU or the related compound thidiazuron was applied to `Simone' and Summerland Selection 535. Both phenylurea chemicals tended to linearly increase cluster weight and berry weight while reducing degrees Brix, pH, and anthocyanins and increasing titratable acidity. A subsequent trial with O, 4, and 8 mg thidiazuron/liter on all four varieties yielded similar results. GA had no individual or synergistic effects. Due to the very low concentrations required, CPPU and thidiazuron show great promise as chemical tools for the increase of berry weight in seedless table grapes. Chemical names used: N-(2-chloro-4-pyridyl) -N'-phenylurea (CPPU); N1-phenyl-N'-l,2,3-thiadiazol-5-yl urea (thidiazuron);

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Fokar Mohamed and Richard Durham

Agrobacterium vitis is the causal organism of crown gall in grapevine. Infection is particularly severe in areas that experience winter damage to vines. Improving resistance to A. vitis will require a detailed knowledge about this organism. In this study, 18 grapevine isolates of A. vitis were collected from different locations near Lubbock, Texas. Isolates were subjected to a phenotypic characterization using 12 biochemical tests, including production of alkali from L-tartrate, production of 3-ketolactose, utilization of citrate, and others. Previously characterized isolates of A. vitis and A. tumefaciens obtained from the American Type Culture Collection served as positive and negative controls in these assays. Isolates were also evaluated for host range, tumor morphology, and opine utilization, and were compared at the molecular level by restriction fragment length polymorphism analysis of the oncogenic regions of the T-DNA plasmid. Although all isolates were able to metabolize tartrate and grow on Roy–Sasser media, there was much variability based on other tests. Twelve of 18 isolates were able to utilize octopine as a sole carbon source. All isolates tested thus far have been pathogenic on tomato and tests on grapevines are underway.