Evaluation of Bait Crops for the Integrated Management of White Rot (Sclerotium cepivorum) in Allium Crops.

Abstract

White rot, caused by Sclerotium cepivorum, is a serious disease that causes significant yield losses in Allium production. The pathogen persists in soil as sclerotia, which germinate in response to sulfur compounds in Allium root exudates. This study was aimed at investigating the potential of early-terminated Allium bait crops to reduce densities of S. cepivorum sclerotia in soil. In growth chamber experiments with white onion (A. cepa cultivar 'Southport White Globe'), red onion (A. cepa cultivar 'Marenge'), sweet onion (A. cepa cultivar 'Walla Walla'), and bunching onion (A. fistulosum cultivar 'Parade'), termination of all four Alliums at the first- and second-leaf stages reduced soil sclerotia populations by up to 62 and 76%, respectively. Examination of soil samples collected 4 weeks after crop termination indicated that sclerotia populations in bait crop treatments remained low when seedlings were terminated at the first- and second-leaf stages. In contrast, crop termination at the third-leaf stage resulted in an increase in sclerotia counts due to the pathogen reproduction on the bait crops. The reduction in sclerotia populations in soil due to early crop termination was also observed in replicated field trials. Greater reductions in sclerotia counts were observed when plants in these experiments were terminated chemically as opposed to mechanically. In-furrow fungicides did not reduce sclerotia numbers under the conditions tested. This study demonstrates the potential for early termination of Allium bait crops to help reduce white rot inoculum in soil.