Incidence of the Endophytic Fungus Acremonium coenophialum in Tall Fescue (Festuca arundinacea) in Japan

Abstract

Mycelium characteristic of endophytic fungi belonging to Acremonium sect. Albo-lanosa was present in seeds of tall fescue from 14 of 39 ecotype collections made throughout Japan. The characteristic mycelium was also detected in one of seven pasture-type commercial cultivars. However, intercellular hyphae were present in the leaf sheaths of plants from only two of the 15 infected seed samples, indicating that the fungus in the other thirteen samples was dead. The death of the fungus probably ocurred because the seeds were stored for 5-7 years after being harvested. The hyphae were detected in tillers of tall fescue from 6 of 9 turf-type cultivars, and their infection rates were 55-90%. The hyphae in the leaf sheaths of infected plants were hyaline, convoluted, infrequently branched, and ran parallel to the vascular bundles. Examination using scanning electron microscopy confirmed that the hyphae were located in the intercellular spaces. Morphological changes such as cell collapse were not observed in the host cells adjacent to the hyphae. Tissue pieces taken from infected tillers and incubated on potato dextrose agar consistently gave rise to slowgrowing white cottony colonies with numerous solitary slender tapering phialides on the aerial hyphae. Each phialide usually produced just a single, non-septate, hyaline, smooth-walled, ovoid to reniform conidium, 6-12μm (mean 10.5μm)×1.3-3.9μm (mean 2.5μm), typically positioned at right angles on the tip of the phialide. All isolates obtained were identified as Acremonium coenophialum MORGAN-JONES et GAMS as reported in tall fescue in many countries.