ASSESSMENT OF THE IMPACT OF NITROGEN SOURCE AND PH ON THE SPRING DEAD SPOT PATHOGENS, OPHIOSPHAERELLA HERPOTRICHA AND O.KORRAE WITH AN IN VITRO MYCELIAL GROWTH ASSAY

摘要

Spring dead spot (SDS) caused by Ophiosphaerella herpotricha (Fr.) J.Walker and O.korrae (J.Walker and A.M.Smith) R.A.Shoemaker and C.E.Babcock,is a serious disease limiting bermudagrass use in the transition zone.Current management practices do not provide adequate control of this disease.Recent field studies indicate nitrogen source and/or pH are important factors that may be manipulated to suppress spring dead spot.Nitrogen source and pH impact on the SDS pathogens Ophiosphaerella herpotricha and O.korrae were assessed using in vitro mycelial growth assays.To assess pH,potato dextrose agar amended with antibiotics was adjusted to pH ranges 3-9 with sodium hydroxide or lactic acid.Calcium nitrate or ammonium sulfate was amended at concentrations of 0-800 ppm to modified Melin-Norkrans medium to investigate nitrogen source impact.Radial mycelial expansion of O.korrae and O.herpotricha isolates was measured after 12 days of growth on the pH and nitrogen amended media.No growth was observed at pH 3.The least amount of growth was at pH 4 when compared to pH’s 5-9 for both species.Growth of O.korrae was greatest on treatments of calcium nitrate,however,growth of O.herpotricha was not statistically different between nitrogen sources.These preliminary findings do not correlate with field research demonstrating suppression of spring dead spot with the use of nitrogen fertilizers.