Systemic modification of cotton root exudates induced by arbuscular mycorrhizal fungi and Bacillus vallismortis HJ-5 and their effects on Verticillium wilt disease

Abstract

Verticillium wilt caused by Verticillium dahliae Klab. limits the production of cotton worldwide. An effort was made to identify the local and systemic plant phenolic acids produced in the presence or absence of an antagonistic strain of Bacillus vallismortis HJ-5 (HJ-5) and an arbuscular mycorrhiza fungus Glomus versiforme (AM) during the incidence of the wilt to explore better ways to control the disease. When V. dahliae and HJ-5 were applied to AM-inoculated soil, the cotton plant disease was decreased especially with the co-inoculation of HJ-5 and AM and the disease index decreased up to 63.3% compared with the control. Four phenolic acids were found in the cotton root exudates, and all the phenolic acids at low concentrations stimulated germination of V. dahliae spores, while higher concentrations were inhibitory. The phenolic acid concentrations in the root exudates decreased significantly with the application of HJ-5 and AM. A split-root system verified that the alterations of the exudation pattern in HJ-5, AM and V. dahliae-inoculated cotton roots were not only local but also systemic. The change in the levels of cotton root exudate phenolic acids partially revealed the mechanism for pathogenesis in Verticillium wilt disease. Our results would be useful in the development of methods to better control cotton wilt disease.