Suppression of microdochium nivale by phosphite in cool-season amenity turfgrasses

Dempsey, John. J

Abstract

The ascomycete fungus Microdochium nivale (Fr.) Samuels and Hallett (teleomorph Monographella nivalis (Schafnitt) is one of the most ubiquitous and damaging pathogens of cool-season amenity turfgrasses. Current control measures rely on inputs of chemical fungicides, making alternative means of disease reduction desirable. Phosphite (PO33-), which is derived from the alkali metal salts of phosphorous acid (H3PO3-),has proven efficacy in reducing susceptibility to oomycete pathogens. The aims of this research were to determine if PO33- treatments to amenity turfgrasses can suppress the incidence and severity caused by M. nivale, to determine the processes involved in such suppression and to assess the effect PO33- treatment had on turfgrass growth and quality. The research produced significant and novel data. In vitro inhibition of M. nivale mycelial growth was determined by amending PDA with PO33- and phosphate (PO43-), with concentrations from 0.5 to 1000 μg/ml-1. It was determined that PO33- concentrations of 100 μg/ml-1 and above, fully inhibited mycelial growth, with EC50 values from 38 to 45 μg/ml-1. PO43- caused no inhibition. Microscopic analysis of hyphal morphology showed distinct irregularities in M. nivale growing on PO33- amended PDA, while on PO43- amended PDA, mycelial growth was normal. Further in vitro studies determined PO33- was fungistatic rather than fungicidal, and that the presence of PO33- in growth media significantly inhibited conidial germination. Field trials determined significantly lower percentages of M. nivale incidence on PO33- treated plots of turfgrass, when compared with untreated controls, with the addition of PO33- significantly enhancing fungicide efficacy. Turfgrass quality on all PO33- treated plots was significantly better than either control or PO43- treated plots. Analysis of PO33- treated turfgrass tissues using High Performance Ion Chromatography, determined rapid in planta accumulation, symplastic mobility and no conversion to PO43- The data also indicate that PO33-, applied sequentially at four week intervals, would maintain leaf tissue amounts of approximately 2000 ppm, but would lead to cumulative accumulations in meristematic tissues. Furthermore, PO33- applications applied sequentially in excess of a six month period, can lead to increases in soil P levels. In phosphorus (P) deficient rootzones foliar applied PO33- does not supply a usable form of P and can repress plant P deficiency responses. In P sufficient rootzones foliar-applied PO33- increases plant biomass, with a reduction in root to shoot ratios. Assessment of turfgrass infection incidences determined M. nivale hyphae are the main source of inoculum and that infection was by means of stomatal penetration. Conidia produced via sporodochia following infection, are the means of propagation and dispersal. Analyses of infected turfgrass confirmed that increased synthesis of phenolic compounds and H2O2 are a component of initial defence responses and that PO33- pre-treatment, enhanced these responses. In conclusion, this work has shown that phosphite, when applied sequentially as a component of a balanced nutrient program, will suppress M. nivale incidence, increase the efficacy of turfgrass fungicides and lead to an enhancement of turfgrass quality. The results of this research will lead to changes in golf green management procedures, resulting in reduced requirements for chemical plant protectants, with added benefits of cost savings and a reduced environmental impact.

Citation

Dempsey, J. J. Suppression of microdochium nivale by phosphite in cool-season amenity turfgrasses. (Thesis). University of the West of England. Retrieved from https://uwe-repository.worktribe.com/output/838673

• Thesis Type: Thesis
• Publicly Available Date: Jun 6, 2019
• Keywords: microdochium nivale, phosphite, turfgrass
• Public URL: https://uwe-repository.worktribe.com/output/838673
• Award Date: Feb 6, 2015