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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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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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(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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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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. 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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(green leaves) of japanese bunching onion [ Allium fistulosum (genomes FF)] greatly affects its quality in terms of texture and health-promoting effects. We previously developed eight A. fistulosum -shallot [ A. cepa Aggregatum group (genomes AA

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Abstract

Interspecific F1 hybrid plants between Allium fistulosum L. and A. cepa L. exhibit bivalent pairing suggesting genomic homology; however, chromosomal variants exist rendering meiotic abnormalities. The occurrence of multivalent associations suggest at least 1 translocation differentiates the 2 species. The chromosome bearing the nucleolus organizer is apparently involved in the translocation. The presence of bridges and fragments in anaphase and telophase I also indicates the occurrence of at least 1 inversion. A minimum of 2 heteromorphic bivalents were observed which probably reflects the translocation and/or inversion(s).

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Abstract

Freshly dehisced pollen of Allium cepa L. was stored under various conditions of temperature and relative humidity for up to 198 days. One series of treatments was freeze dried before storage. The degree of viability was determined by germination percentages at periodic intervals. Germination of approximately 60% of the initial germination was maintained in pollen samples freeze dried and stored at −18° and 5% relative humidity. Without freeze drying, approximately 38% of initial germination was maintained in samples of onion pollen stored 198 days at −18° and 10% relative humidity. Pollen stored at −18° and 80% relative humidity germinated 34% of initial germination after 56 days of storage and gradually declined to 4% by 170 days.

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Greenhouse and field methods were developed to screen Allium spp. for resistance to Botrytis leaf blight (caused by Botrytis squamosa Walker). In the green-house, plants were sprayed with laboratory-grown inoculum and incubated in a temperature-controlled enclosure containing an atomizing mist system. For field inoculations, a portable misting system with windbreaks was erected, and the plants were sprayed with laboratory-grown inoculum. Greenhouse and field incubation conditions maintained leaf wetness without washing inoculum from the leaves. Botrytis leaf blight symptoms in greenhouse and field evaluations were identical to symptoms in commercial onion fields. A total of 86 selected USDA Allium collection accessions were evaluated using these methods. All A. fistulosum accessions and A. roytei were highly resistant to immune, as were most accessions of A. altaicum, A. galanthum, A. pskemense, and A. oschaninii. Nearly all of the A. vavilovii and A. cepa accessions were susceptible. However, one A. cepa accession (PI 273212 from Poland) developed only superficial lesions, which did not expand to coalesce and blight leaves. This work confirms previous reports of Botrytis leaf blight resistance in Allium spp., and suggests that strong resistance exists with A. cepa.

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Cytogenetic studies were performed on Allium fistulosum, A. cepa. their F1 hybrid, and ten backcross (BC1) progenies [(A. fistulosum × A. cepa) × (A. cepa) 1. In meiosis the F1 hybrid showed 41 percent hetercmorphic bivalent pairing with 10.6 +. 1.8 `chiasmata per cell. Meiocytes were observed with one, two and three bridges and fragments, indicating at least three paracentric inversions. Multivalent associations indicate at least two translocations, one involving the satellite chromosome. The percentage of bivalent pairing, bridges and fragments, and multivalent associations varied in BC1 progenies. The F1 hybrid and all of the BC1 plants were either sterile or had very little seed set. The satellite chromosomes used as cytological markers showed variation in nucleolus position, degree of attachment and number.

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