Differentiation of Trichoderma taxa associated with mushroom production

A major epidemic of green mould in mushroom compost in Northern Ireland lasting for 6 months was caused by a single taxon of Trichoderma harzianum (Th2). This has continued to be the principal taxon causing losses in Ireland over a 9-year period. A separate taxon, Th4, is responsible for a more recent epidemic in North America. Cultural methods are described which aid rapid differentiation of four distinct taxa of T. harzianum and five other species from the mushroom environment. After developing a standard cultural method, isolates were grouped visually by features such as growth rate at 27 degrees C, amount of aerial mycelium, and the effect of light on sporulation form and timing. Most of these groups of isolates had significantly different growth rate ratios from each other at 27 degrees C/17 degrees C, Furthermore isolates within groups which had been separated by culture features alone were closely homologous as regards their microscopic morphological features such as phialides and phialospores. Two factors underlining the importance of using a standard cultural method in aiding identification were that culture morphology was shown to vary widely on different media and spore size was found to vary significantly with incubation temperature. Some difficulties are discussed concerning differentiation of Trichoderma spp. using classical microscopic features alone.