Combining antagonistic endophytic bacteria in different growth stages of cotton for control of Verticillium wilt

Abstract Verticillium wilt of cotton is a major limiting factor in cotton production. To investigate the combined control effects of endophytic bacteria in different growth stages of cotton on Verticillium wilt, antagonistic bacteria Paenibacillus xylanilyticus YUPP-1, Paenibacillus polymyxa YUPP-8 and Bacillus subtilis YUPP-2 were isolated from cotton in the seedling, squaring and boll-setting stages, respectively. Assessment of colonization showed that strains YUPP-1, YUPP-8 and YUPP-2 had the highest populations in the seedling, squaring and boll-setting period, respectively. Indoor pot experiment indicated that cotton plants in the combined biocontrol bacteria treatment group were not infected before squaring stage, while infection rates of cotton treated with a single strain in the seedling period were 6.7% (strain YUPP-8), 6.7% (strain YUPP-1) and 13.3% (strain YUPP-2). However, infection rate of the control plants reached 80%. Field experiment conducted during 2010–2011 showed that the combined application of three strains had better effect than individual application. Verticillium wilt morbidity rate and disease index of cotton at the boll-setting period with combined application of three strains in 2010 were 9.4% and 6.5, respectively, while those in the control group were 47.5% and 32.8. The results in 2011 were similar to 2010, with higher disease severity in both treated and control plants. These results illustrated that combined application of endophytic bacteria can achieve good control effects against Verticillium wilt of cotton. This study provides a new strategy for the control of soil-borne diseases.