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Jen Colcol Marzu, Elizabeth Straley and Michael J. Havey

introgression of the PR resistance on chromosome 4 into diverse onion populations. Table 3. Sequences of single nucleotide polymorphisms (SNP) on chromosome 4 of onion mapping within the 1.5 logarithm of odds (LOD) confidence interval for pink root-resistance in

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Christopher S. Cramer

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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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Andrew C. Ludwig, John F. Hubstenberger, Gregory C. Phillips and G. Morris Southward

Callus cultures were established from intraspecific lines of Allium cepa L., interspecific F1 progeny of A. cepa crossed to A. fistulosum L. and to A. galanthum L., advanced generations of A. fistulosum x A. cepa backcrossed to A. cepa, and lines of A. fistulosum and A. galanthum. These genotypes had been identified as susceptible, resistant, or partially resistant tester lines based on prior seedling and field nursery screenings using the pink-root pathogen Pyrenochaeta terrestris (Hansen) Gorenz, Walker and Larson. Tester line calli were challenged in vitro with culture filtrates of the fungal pathogen and were assessed by visible damage ratings expressed as the percentage of pigmentation in response to the filtrate. The degrees of callus sensitivity to the filtrate observed in vitro corresponded well with the in vivo tester line classifications. These results eliminated the possible confounding influence of using various species of Allium for in vitro screening. Our results indicated the suitability of the in vitro screening approach for the possible identification of useful segregants or somaclonal variants possessing pink-root resistance. However, in vivo pathogenicity may involve mechanisms in addition to sensitivity to the putative toxins present in the filtrate.

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Christopher S. Cramer, Jose L. Mendoza and Joe N. Corgan

Current emphasis of onion breeding programs has been to develop male-sterile, maintainer, and pollinator inbred lines for the production of hybrid cultivars. Five short-day, male-sterile inbred lines from the New Mexico State Univ. Onion Breeding Program were crossed to four short-day, pollinator inbred lines in all possible combinations. In addition, six intermediate-day male-sterile inbred lines were crossed with seven intermediate-day, pollinator inbred lines in all possible combinations. The resulting hybrid lines from all crosses were evaluated for maturity, bolting resistance, pink root resistance, Fusarium basal rot resistance, percentage of marketable bulbs, marketable yield, average bulb weight, and percentage of bulbs with single centers. The average performance among male-sterile and among pollinator lines within each group was determined by averaging over hybrid lines that pertained to the respective male-sterile or pollinator line. Among the short-day inbred lines, NMSU 97-28-2 and NMSU 97-109-2 as female parents produced the best hybrid lines, while NMSU 96-17-1 and NMSU 96-51-1 as male parents produced the best hybrid lines. The best hybrid combinations among the short-day parents were NMSU 97-28-2 × 96-17-1 and 97-46-2 × 96-51-1. Among the intermediate-day inbred lines, NMSU 96-196-2 and 96-300-2 as female parents produced the best hybrid lines, while NMSU 96-280-1, NMSU 96-274-1 and 96-395-1 as male parents produced the best hybrid lines. Some of the best intermediate-day hybrid combinations included NMSU 96-300-2 × 96-335-1 and NMSU 96-300-2 × 96-274-1.

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Christopher S. Cramer and Joe N. Corgan

1964 ( Havey, 2007 ). ‘Early Supreme’ produces very large to jumbo-sized, pungent, flattened globe-shaped bulbs that have very good pink root resistance, intermediate fusarium basal rot resistance [causal agent, Fusarium oxysporum f. sp. cepae (H

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Theodore J. Kisha and Christopher S. Cramer

Bark (1994) suggested that the source of pink root resistance came from Excel 986 A, a male-sterile line used in the development of the hybrid cultivar Granex 33, and possesses sterile-type (S) cytoplasm. In doing so, the PRR strains of ‘Texas Early

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Christopher S. Cramer

increase pink root resistance was made from a greenhouse seedling screening for pink root susceptibility. These bulb selections were placed as nine separate entries within a cage designated as 92-65. In addition, a second selection for earlier bulb maturity

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Christopher S. Cramer and Joe N. Corgan

onion that was developed by Dessert Seed Co. in 1964 ( Havey, 2007 ). ‘Early Supreme’ produces very large to jumbo-sized, pungent, flattened globe-shaped bulbs that have very good pink root resistance, intermediate fusarium basal rot resistance {causal

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Christopher S. Cramer

because it is short-day in its maturity, expresses a high level of pink root resistance, and produces an extensive root system (J.N. Corgan, personal communication, 2013). When bulbs of both entries flowered in May of 1981, pollinators were introduced to