Sensitivity of Alternaria solani to boscalid and control of boscalid resistance with commonly-used fungicides in Shanxi, China

摘要

Early blight, caused by Alternaria solani, is a foliar disease of cultivated tomatoes, affecting both tomato yield and quality. Boscalid was first introduced to China in 2008 to control tomato early blight. However, knowledge on the sensitivity of A. solani to boscalid is lacking after 5 years of field application. In this study, 100 A. solani isolates were collected from five distantly separated localitions in Shanxi Province in China, to investigate the sensitivity of A. solani to boscalid, and to evaluate the control efficacy of commonly-used fungicides against boscalid-resistant A. solani strains on leaf discs. The EC50 values and the resistance indexes to boscalid of these isolates ranged from 0.31 to 164.20 mu g center dot mL(-1) (mean = 12.94 mu g center dot mL(-1), SD = 25.01) and from 0.28 to 0.49 (mean = 0.38, SD = 0.08), respectively. Field isolates of A. solani in Shanxi Province varied in their sensitivities to boscalid. Among these isolates, 54 % showed resistance to boscalid, and 76 % of the resistant isolates had moderate resistance (R-M) against boscalid. Boscalid-resistant isolates were most frequently observed in the Xinzhou and Yuncheng districts, and the only two highly-resistant isolates in this study were detected in Xinzhou. No cross-resistance was detected between boscalid and the commonly-used fungicides, pyrisoxazole, difenoconazole, polyoxin, and sandofan. These non-boscalid fungicides could significantly suppress disease development caused by A. solani with different boscalid resistance levels, and polyoxin provided a control efficacy equal to or better than the other three fungicides. Polyoxin could play a key role in early blight management and should be recommended in a control strategy for boscalid resistance based on the application of multiple fungicides or in alternation with different fungicides throughout the growing season.