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Subhankar Mandal and Christopher S. Cramer

types (cut vs. intact) and three Fusarium oxysporum f.sp. cepae (Hanzawa) Snyder & Hansen (FOC) concentrations and their interactions. Fig. 4. Changes in ( A ) fusarium basal rot (FBR) severity and ( B ) FBR incidence depending on basal plate

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Jessica A. Gutierrez, Ramon Molina-Bravo, and Christopher S. Cramer

Fusarium basal rot (FBR), caused by Fusarium oxysporum f.sp. cepae, is a soilborne fungal disease that affects bulb onions (Allium cepa) worldwide. Winter-sown onion cultivars that are resistant to FBR are lacking. The goal of this project was to screen winter-sown onion germplasm for FBR resistance using a mature-bulb field screening at harvest and after 4 weeks in storage. The project was conducted for 2 years, and in each year, 22 winter-sown onion lines were grown in a field known to produce a high incidence of FBR-infected bulbs. At maturity, the basal plates of 20 randomly selected bulbs were cut transversely and each plate was scored for disease severity on a scale of 1 (no diseased tissue) to 9 (70% or more diseased tissue). Bulbs were stored and scored again at 4 weeks after harvest. Severity and incidence increased in storage for both years. NMSU 99-30, `NuMex Arthur', and `NuMex Jose Fernandez' showed the lowest disease severities and incidences in both years. For fields that produce a high incidence of FBR-infected bulbs, these cultivars could be grown with less loss to FBR at harvest and after storage than more FBR-susceptible cultivars. When developing FBR-resistant cultivars, breeding lines should be evaluated over multiple years and bulbs should be stored for 4 weeks before being screened.

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Jessica A. Gutierrez and Christopher S. Cramer

Fusarium basal rot (FBR), caused by Fusarium oxysporum Schlechtend.:Fr. f. sp. cepae (H.N. Hans.) W.C. Snyder & H.N. Hans, is a soilborne fungal disease that affects bulb onions (Allium cepa L.) worldwide. Short-day onion cultivars that are resistant to FBR are lacking. The goal of this project was to screen fall-sown onion germplasm for FBR resistance using a mature bulb field screening at harvest and after 4 weeks in storage. The project was conducted for 2 years, and in each year, 26 fall-sown onion lines were grown in a field known to produce a high incidence of fusarium-basal-rot-infected bulbs. When all the bulbs in a plot were mature, the basal plates of 20 bulbs were cut transversely and each plate was rated for disease severity on a scale of one (no diseased tissue) to nine (70% or more diseased). Bulbs were stored and rerated at 2 and 4 weeks after harvest. Disease severity and incidence were higher in the first year than in the second year. Both severity and incidence increased as bulbs were stored for 4 weeks. NMSU 00-25 exhibited the lowest disease severity and incidence in both years at harvest time and after storage. `Buffalo' and `Cardinal' exhibited the highest severities and incidences across both years and at harvest time and after storage. Other entries exhibited high or low disease severity and incidence but not consistently across years and between harvest time and after storage. In the development of FBR resistant cultivars, breeding lines should be evaluated over multiple years and bulbs should be stored for 4 weeks before being screened.

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Swee-Suak Ko, Woo-Nang Chang, Jaw-Fen Wang, Shin-Jiun Cherng, and S. Shanmugasundaram

In the tropics, onion (Allium cepa L.) bulbs are usually stored in shelters under ambient conditions resulting in severe storage losses. This study was aimed at determining whether variation in bulb storability exists among short-day onion cultivars and whether the trait can be improved through conventional breeding. Twelve onion cultivars with different degrees of storability were selected from preliminary experiments. Bulbs of selected cultivars were grown and stored for 3 months under ambient conditions. Observations were made on disease incidence at harvest, percentage diseased bulbs, and storage disease incidence of bacterial soft rot [BR (Pseudomonas gladioli pv. alliicola Burkholder)], black mold [BM (Aspergillus niger Tiegh.)], and fusarium basal rot (Fusarium oxysporum Schlechtend.:Fr. f. sp. cepae) after 3 months of storage. Data on bulb characteristics such as bulb fresh weight (FW), dry matter (DM) content, total soluble solids (TSS), and pyruvic acid content were recorded at harvest. Mean storage losses of cultivars ranged from 21% to 99% over 3 years. Diseases were the major causes of storage losses, with BR and BM being the most predominant. Performance of most traits (including storage losses) was significantly influenced by year (Y), cultivar (G), and Y × G interaction. Heavy rainfall during bulb development in 1997 may have contributed to higher disease incidence at harvest, higher percentage of diseased bulbs during storage, and lower DM, and TSS of the cultivars. Cultivars with good storability, such as `Red Pinoy' and `Serrana', were less sensitive to stressful environments and high disease pressure. Incidence of storage diseases was significantly correlated with DM (r = -0.65 to -0.84) and TSS (r = -0.66 to -0.87), as well as incidence of BR (r = 0.57 to 0.94) in each year. Thus, they could be good indicators for evaluating storability. Cultivars with good storability tended to have small bulbs, as average bulb FW was positively correlated with incidence of storage diseases. Disease incidences on `Red Pinoy' and `Serrana', both in the field and in storage, were significantly lower than in the other cultivars, indicating they are tolerant to major storage diseases and that they could be used as donor parents for genetic improvement of onion storability.

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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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Christopher S. Cramer and Joe N. Corgan

agent, Fusarium oxysporum f. sp. cepae [(H.N. Hans.) W.C. Snyder & H.N. Hans]}, and good bolting tolerance ( Anonymous, 2007 ). ‘Early Supreme’ is not currently grown in New Mexico as a result of its poor adaptation. ‘Southport White Globe

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Christopher S. Cramer and Joe N. Corgan

. Two onion diseases that are present at high levels in our evaluation fields are pink root and fusarium basal rot (FBR) [causal agent, Fusarium oxysporum f. sp. cepae (H.N. Hans.) W.C. Snyder & H.N. Hans]. Replicated variety trials over the past 10

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Jen Colcol Marzu, Elizabeth Straley, and Michael J. Havey

. 64 450 454 Klingner, A. Pontis-Videla, R.E. 1961 Pink root disease of onions in Mendoza, Argentina Plant Dis. Rpt. 45 235 Lacy, M.L. Roberts, D.L. 1982 Yields of onion cultivars in Midwestern organic soils infested with Fusarium oxysporum f. sp

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Lina M. Rodríguez-Salamanca and Mary K. Hausbeck

Fusarium basal rot incited by Fusarium oxysporum f. sp. cepae (H.N. Hansen) W.C. Snyder & H.N. Hansen, but their response to C. coccodes has not been evaluated. The occurrence of this pathogen constitutes a new challenge for onion growers in Michigan

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Clinton C. Shock, Erik Feibert, Lynn Jensen, S. Krishna Mohan, and Lamont D. Saunders

these trials include bulb yield and size, maturity rating, potential for bolting, and susceptibility to neck rot ( Botrytis allii and Botrytis aclada ) and plate rot ( Fusarium oxysporum f. sp. cepae ) diseases ( Shock et al., 2000 ). Starting in