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William Randle, Orville Lindstrom and Daniel Warnock

The onion crop in Georgia is often damaged by suboptimal winter temperatures. Proper acclimation of seedlings is a way of limiting freeze damage. Because photoperiod is among the factors involved in plant acclimation, the effects of photoperiod on the acclimation of short-day Allium cepa seedlings was investigated. A single short-day cultivar, 'Granex 33', was greenhouse grown under an eleven hour photoperiod. After ten weeks of growth, four photoperiod treatments (8, 11, 14, and 24 hrs.) were administered during a two week hardening period at 3* C. Plants were then frozen in an ethylene glycol bath. Degree of acclimation was determined based on regrowth and visual observation. Acclimation of seedlings was completely inhibited by the 24 hour photoperiod. Varying degrees of acclimation were achieved with the other photoperiod treatments.

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Juan Carlos Díaz-Pérez, Jesús Bautista, Gunawati Gunawan, Anthony Bateman and Cliff Martin Riner

Vidalia onions ( Allium cepa L.) are sweet, short-day, low pungency, yellow Granex-type bulbs that are popular in the United States because of their mild flavor ( Boyhan and Torrance, 2002 ). Vidalia onions are exclusively grown in Southeastern

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Ockyung H. Bark, Michael J. Havey and Joe N. Corgan

The edible Alliums are economically important world-wide. The bulb onion (Allium cepa) is the most widely grown. The Japanese bunching onion (A. fistulosum) has many desirable characters, e.g., resistance to pink root, Thrips, smut, maggot, and Botrytis. Transfer of pink root resistance from A. fistulosum into A. cepa has been attempted for over 60 years. However, sterility of the F1 hybrid is a barrier and there is little evidence of gene introgression during backcrossing to A. cepa. Dr. Corgan has made crosses between A. fistulosum as the seed parent and A. cepa. He backcrossed the F1 hybrids to A. cepa and generated BC2 progenies which showed excellent pink root resistance. RFLPs in the chloroplast genome showed all BC2 progenies had either the normal or sterile cytoplasm of A. cepa. This may be due to not strictly maternal inheritance of the chloroplast DNA or a seed mixture during backcrossing. Other interspecific hybrids and their BC1 progenies had the cytoplasm of A. fistulosum. Nuclear RFLPs show hybrid patterns in the F1 plants. BC1 progenies possess some A. fistulosum markers as evidence of DNA introgression from A. fistulosum into the backcross progenies.

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Shigenori Yaguchi, Tetsuya Nakajima, Toshihisa Sumi, Naoki Yamauchi and Masayoshi Shigyo

162 Galmarini, C.R. Goldman, I.L. Havey, M.J. 2001 Genetic analyses of correlated solids, flavor, and health-enhancing traits in onion ( Allium cepa L.) Mol. Genet. Genomics 265 543 551

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Paul Mangum and Ellen Peffley

(Allium cepa × A. fistulosum) × A. cepa breeding lines have been established to the fourth generation. The aim is to develop an A. cepa-like bulbing onion carrying A. fistulosum genes. Seven populations were characterized for morphological traits and three isozyme markers. Each bulb from the populations was characterized for maturity, soluble solids content, bulb shape, and bulb color. All the populations produced A. cepa-like bulbs. Significant variation was observed within each population for each morphological trait. All the bulbs were screened for the presence of A. cepa and A. fistulosum alleles of alcohol dehydrogenase (Adh-1), esterase (Est), and phosphoglucoisomerase (Pgi-1). Allium cepa Adh-1, Est, and Pgi-1 alleles were observed in all the populations. One population, 951026-8, contained plants heterozygous for A. cepa and A. fistulosum Pgi-1 alleles. Recovery of these fourth generation Allium backcross plants demonstrates introgression of the A. fistulosum genome into an A. cepa-like bulbing onion.

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Shigenori Yaguchi, Masanori Atarashi, Masatoshi Iwai, Shin-ichi Masuzaki, Naoki Yamauchi and Masayoshi Shigyo

. A complete set of A. fistulosum – Allium cepa Aggregatum group monosomic addition lines (2 n = 17, FF+1A–FF+8A) was established in our previous study ( Shigyo et al., 1996 ). This series displays morphological and physiological characteristics

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Erin M. Silva, Bill B. Dean and Larry Hiller

Successful pollination of onion (Allium cepa L.) flowers greatly depends on adequate nectar production. In order to understand the nectar production dynamics of onion flowers, nectar was collected at regular intervals during a 24-hour period. Hourly nectar volumes were compared to a variety of environmental conditions, including amount of solar radiation, relative humidity, temperature, wind speed, and evapotranspiration. Production patterns showed mid- to late-morning peaks and late evening peaks in nectar volume. Nectar appeared to be reabsorbed by the flowers during the afternoon and overnight hours. Individual flowers produced the highest amount of nectar several days after initially opening. Nectar production was significantly and inversely related to relative humidity while the effects of temperature, evapotranspiration, wind speed and solar radiation on nectar production were not significant in this study.

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Daniel Warnock, William Randle and Mark Rieger

Photosynthesis is the very essence of agriculture. Previous photosynthetic and transpirational studies of onion (Allium cepa) have been limited to specific developmental stages. Our study measured photosynthesis and transpiration in sixteen plants of a single short-day cultivar over an eleven week period containing both non- and bulb inductive photoperiods. Differences in weekly means for photosynthesis, leaf conductance, water use efficiency, and intercellular CO, were highly significant. Weekly photosynthetic means increased under a non-inductive photoperiod and peaked one week after initiating a bulb inducing photoperiod. A decrease and leveling period occurred as bulbs developed followed by a decrease as foliage lodged. Weekly photosynthetic and leaf conductance means were correlated and highly significant. Water use efficiency and intercellular CO, means remained fairly constant throughout the study suggesting that photosynthesis in unstressed onions was controlled by internal mechanisms instead of stomata.

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Renee M. Schloupt, Walter E. Splittstoesser and Robert M. Skirvin

The objective of this research was to induce vitrification in onion (Allium cepa L. cv. `White Ebeneezer'); then use this information to make suggestions on how to avoid vitrification of micropropagated plants. There were no differences in vitrification percentage when shoot tip explants were isolated, sterilized and placed on MS medium (8 g.L-1 agar) supplemented with 0.16 uM NAA and varying (0.0 to 70.0 uM) levels of BA. When agar was replaced by gelrite (MS medium with 4.4 uM BA and 0.16 uM NAA), vitrification increased when gelrite concentrations decreased from 2.0 to 1.0 g.L-1. More vitrification occurred when shoot tips were supported on a synthetic cosmetic puff in liquid medium or when agar was reduced to 4.0 g.L-1 than when supported on a cosmetic puff in 8 g.L-1 agar or on 8 g.L-1 agar alone.

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M. Kopelberg, I.L. Goldman, J.E.P. Debaene and B.S. Schwartz

Onion (Allium cepa L.) and other vegetable Alliums have long been recognized for the antiplatelet properties. Consumers may benefit from the medicinal value of onions because they are commonly eaten raw in salads and the antiplatelet factor is destroyed by heat. Recent work indicates antiplatelet activity in Allium sp. may be due to the presence of native organosulfur compounds. The concentration of organosulfur compounds correlates positively with pungency, varies with onion cultivar, and is influenced by environmental factors. Bulb dry matter content, or solids, is positively correlated with pungency. Because antiplatelet activity may also be based on the activity of organosulfur compounds, it is possible these three factors are significantly correlated. The objective of this investigation was to examine the relationship among pungency, solids, and antiplatelet activity in four diverse onion genotypes. Replicated trials consisting of two mild and two pungent genotypes were conducted at four locations in 1994. Onion bulbs were harvested and analyzed for all three traits. Results from this investigation indicate significant positive correlations between antiplatelet activity, pungency, and solids in onion.