Biocontrol potential of Ampelomyces quisqualis strain CPA-9 against powdery mildew: Conidia production in liquid medium and efficacy on zucchini leaves

Abstract

Ampelomyces quisqualis has been reported to be a promising biocontrol agent (BCA) against powdery mildew, and it has been commercialised as AQ10 Biofungicide®. However, isolated strains showed inconsistent results when applied under practical conditions, and research to find a thoroughly effective strain is still in progress. In addition, asexual spores of the BCA are required to parasitise powdery mildew; however, producing a high amount of conidia is difficult. The present study aimed to select of an effective strain of A. quisqualis against powdery mildew on zucchini leaves and to test its conidiation in liquid media. The efficacy of several isolates from cucurbits were tested and the most effective was identified as A. quisqualis CPA-9, which reduced powdery mildew on zucchini leaves up to 61.5 % when it was applied at 2.5 × 105 conidia/mL. Conidial production of CPA-9 in liquid media was optimised, and several growing conditions were tested, such as the medium, agitation, and incubation time. Asexual reproduction was induced by modifying the aw of the media or reducing agitation. A concentration of 7.3 × 107 conidia/mL was achieved in 500-mL Erlenmeyer flasks containing 75 mL of potato dextrose broth modified with 2.5 % (w/v) of glycerol incubated at 25 °C for 11 days in the dark and without agitation. The produced conidia of CPA-9 maintained the biocontrol efficacy against P. xanthii on zucchini plants and reduced the disease incidence by up to 83 %.