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Detection of Systemic and Latent Presense of Botrytis allii in Onion Transplants 2006

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Project Leaders: J. Lorbeer , Department of Plant Pathology, Cornell; C. Hoepting , Cornell Cooperative Extension, Vegetable Program

Cooperators: Western and Central New York Onion Growers

In New York, major outbreaks of Botrytis neck rot of onion, caused by Botrytis allii have occurred in association with the recent increases in growing onions from transplants.  It has been suspected that bare-root transplants grown in Arizona could be infected with B. allii before they are transplanted in New York.  The present study conducted during 2006 endeavored to survey onion transplants for B. allii contamination, to elucidate the main source of this contamination and its role in Botrytis neck rot loss in storage, and to compare the data with that developed from a preliminary and similar study conducted during 2005.  In the present study which involved 50 entries (variety by grower), 81.3% of the bare-root transplants had some level of latent B. allii, compared to 0% for plug transplants and 0% for direct seeded seedlings.  Raw and treated seed, bare-root transplants, and direct seeded seedlings, all of the same lot number, had 71.4%, 0%, 90% (of the bundles) and 0% B. allii, respectively.  In the 2005 study which involved 35 entries, 77.8% of the bare-root transplants had some level of latent B. allii.  The feasibilities of growing bare-root transplants free of B. allii, thereby preventing spread of B. allii from contaminated transplants, and using plug transplants free of B. allii as an alternative to the bare-root transplants should be considered by New York onion growers and could be utilized as procedures to reduce and hopefully eliminate the occurrence of Botrytis neck rot of onion bulbs in storage.