ECOLOGICAL DYNAMICS OF BURKHOLDERIA CEPACIA CAUSING CANKER- SOUR SKIN OF ONIONS AND INTEGRATED PEST MANAGEMENT APPROACHES LEADING TO CONTROL OF THE DISEASE

J. S. Haudenshield, J. W. Lorbeer, N. A. Gundershiem, and G. L. Mark

Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Phone: (607) 255-7875; Fax: (607) 255-4471; Email: JWL5@CORNELL.EDU

The bacterial canker-sour skin disease of onions, caused by B. cepacia, results from infection in the leaf axil by windblown or rainsplashed soilborne inoculum, followed by the formation of the canker symptom at the leaf base, and eventually sour skin in the maturing bulb. The disease has not been controlled in our studies with antibiotics, copper formulations, fungicides, or the elicitor Messenger. Disease management presently involves undercutting and windrowing mature bulbs to completely dry the inner neck tissues of mature plants and prevent infection of healthy bulbs during topping. A program for control of canker under field conditions is needed. Sampling of organic soil from several fields under continuous onion production over four growing seasons, with quantification of their respective B. cepacia populations, has demonstrated a mid-summer rise in B. cepacia, a decline as the plants mature, and a post-harvest rise to high levels. Data collected from similarly sampled fields during or following rotation, or after winter-covercropping, on non-onion crops suggest this approach may contribute toward an integrated pest management program to control canker. Some crops such as turfgrass and radish do not support high B. cepacia populations, whereas others such as corn and leek do. A laboratory miniculture system devised to examine the effects of a variety of plants on rhizosphere B. cepacia levels has provided evidence that some plants, such as carrots, beets, radish, and lettuce can suppress soil population levels of B. cepacia, while others such as corn and soybean can increase the population levels.

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