LAUSR

© 2018 British Society for Plant Pathology The ascomycete fungus Microdochium nivale is a major pathogen of many species of the gramineae. Control measures rely heavily on chemical fungicides, making alternative means of disease reduction desirable. Phosphite (PO33−), has proven efficacy in reducing susceptibility of different species of gramineae to oomycetes, and has adverse effects on the invitro growth of numerous other pathogens. The effect of phosphorous acid (H3PO3), phosphoric acid (H3PO4), dihydrogen potassium phosphite (KH2PO3), dihydrogen potassium phosphate (KH2PO4) and potassium hydroxide (KOH) on the invitro mycelial growth and development of M. nivale was determined. Radial growth on amended potato dextrose agar (PDA) was used to calculate mean daily growth and percentage inhibition. PO33− had a significant inhibitory effect on mycelial growth, with EC50 values ranging between 35.9 and 40.99μgmL−1, whilst PO43− and KOH had no significant inhibitory effect. Microscopic examination of mycelia showed morphological deformities in hyphae growing on PO33− amended PDA, whilst hyphal growth was normal on PO43− and KOH amended PDA. Conidial germination of M. nivale was significantly reduced following immersion in solutions of 50, 100 and 250μgmL−1 of PO33−, while PO43− and KOH at the same concentrations induced no inhibitory affect. These results show that PO33− is a significant inhibitor of the growth of M. nivale and may have the potential to be used as a chemical control agent in the field.