Effects of broccoli residue on the cauliflower-Verticillium dahliae host-pathosystem

摘要

The Salinas Valley is one of the world's most important vegetable producing areas. This valley is located in Monterey County, the fourth largest agricultural producing county (1.94 billion dollar gross value in 1996) in California, U.S.A. Cauliflower (Brassica oleracea var. botrytis) is one of the important vegetable crops in the Salinas Valley, with 9,540 ha planted in 1996 and having a value of 125 million dollar. In recent years, Verticillium dahliae has become an important pathogen of cauliflower in coastal California. In heavily infested fields, microsclerotia (ms) populations are as high as 93 ms/g of dry soil, which can result in greater than 90 percent wilt incidence in the summer-planted cauliflower crop. Resistant cultivars are not available, and the application of methyl bromide + chloropicrin is generally uneconomical. The potential withdrawal of methyl bromide would further limit control choices. Although broccoli (Brassica oleracea var. botrytis) is closely related to cauliflower, commercial plantings have never been infected with V. dahliae even when planted in the summer in high-inoculum density fields that caused significant losses to cauliflower (Table 1). Cauliflower isolates are only weakly pathogenic to broccoli, and ms havenot been observed on broccoli roots. Because of broccoli's apparent status as a non-host of V. dahliae and the known fungicidal properties of crucifer residues, we conducted a series of studies to investigate the usefulness of broccoli residues in suppressing Verticillium wilt of cauliflower.