Occurrence of the fungal endophyte Neotyphodium coenophialum in leaf blades of tall fescue and implications for stock health

Leaf blades of tall fescue (Festuca arundinacea) plants infected with the endophytic fungus Neotyphodium coenophialum (= Acremonium coenophialum) have often been assumed to be endophyte-free. However, fungal colonies identified as N. coenophialum developed following incubation of surface-sterilised leaf blades from endophyte-infected tall fescues on antibiotic potato dextrose agar. A standardised fungal isolation technique was developed to assess the distribution of hyphae within tall fescue leaf blades in three USA-bred cultivars ('Georgia 5', 'Kentucky 31', 'Jesup') and a roadside population (MRSP) from the Manawatu region, New Zealand. Leaf blades of the three USA-bred cultivars were typically sparsely colonised. In contrast, extensively colonised leaf blades were present in many MRSP plants, particularly in autumn. Ergovaline concentrations of up to 3.9 ppm (mean 2.5) were present in leaf blades of the MRSP grown in a glasshouse. Ergovaline at lower concentrations (mean 0.4 ppm) was also detected in leaf blades of the tall fescue cultivars infected with their natural endophytes. These unusually high concentrations of hyphae and ergovaline observed within leaf blades of the MRSP provide an explanation of why fescue toxicosis has been especially severe in New Zealand. Significantly, N. coenophialum from plants of the MRSP was not uniform in cultural characteristics and conidial length, or in the ability to colonise leaf blades and produce ergovaline in artificially infected plants of four diverse tall fescue cultivars. The four inoculated cultivars ('Georgia 5', 'Grasslands Roa', 'Kentucky 31', 'KFa949') also differed in their interaction with N, coenophialum from MRSP. The most colonised leaf blades were in plants from an experimental cultivar of Mediterranean origin (KFa949), and, surprisingly, ergovaline concentrations were higher in the leaf blades than sheath. The New Zealand-bred tall fescue cultivar 'Grasslands Roa' was also distinctive in that no hyphae were detected in leaf blades. The concentration of ergovaline present in pooled leaf blades of 'Grasslands Roa' plants was lower than in those of the other naturally and artificially infected tall fescue/N. coenophialum populationsexamined in this study, reflecting the apparently low concentrations of hyphae present.