Suppressive and preventive activity of chemical disinfectants against sclerotia of Verticillium dahliae in water

Disinfectants have been widely assessed against conidia, zoospores and mycelial growth of fungal plant pathogens in water, however, studies against sclerotia or melanized structures are limited. The disinfectants OX-VIRIN®, OX-AGUA AL25® and Deccoklor® reduce Verticillium dahliae conidia in water, but their potential efficacy in reducing sclerotia of the pathogen in water remains unknown. In this study, sclerotia of six V. dahliae isolates differing in virulence were exposed in vitro to a range of concentrations of the mentioned disinfectants for 30 days to evaluate the suppressive efficacy. In addition, concentrations with higher suppressive effect were tested for their preventive efficacy by means of assays where treated water was subsequently infested. Concentration and monitoring time (1 min, and 5, 15 and 30 days post-chemical treatment; dpc) were the critical factors for the efficacy of the chemicals, whereas variations depending on isolates virulence were negligible. The three highest concentrations of OX-VIRIN® (3.2-51.2 mL L−1) and the two highest concentrations of OX-AGUA AL25® (0.4175 and 1.2525 mL L−1) showed an average suppressive efficacy ranging from 87.8 to 100% and 99.2-100% at the last three sampling times, respectively. Deccoklor® was ineffective at the evaluated concentrations. The three highest concentrations of OX-VIRIN® and the highest concentration of OX-AGUA AL25® maintained a preventive efficacy above 97 and 95%, respectively, at all sampling times. For OX-AGUA AL25® at 0.4175 mL L−1, the preventive efficacy fluctuated over sampling time, but it was of at least 68.9% at 30 dpc in repeated experiments.