EFFECTS OF WATER ACTIVITY AND TEMPERATURE ON THE GROWTH OF FUNGI INTERACTING ON BARLEY-GRAIN

Gemination, growth and interactions of Aspergillus flavus, Penicillium verrucosum, Fusarium poae and Hyphopichia burtonii, either alone or i n the presence of another species, were observed at water activities o f 0.97, 0.95 or 0.90 a. and at 20 or 30-degrees-C, both on the surface of individual barley grains by scanning electron microscopy and on th in layers of grain with a stereomicroscope. By both methods, each spec ies exhibited characteristic linear growth rates which changed with a. and temperature. Spore germination was unaffected by the presence of another species, but distinct interaction patterns between competing s pecies on the grain surface were identified, which were determined by rate of hyphal extension and branching, namely (a) faster growth of on e species causing progressive inhibition of the slower-growing species ; (b) faster growth initially of one species which is then inhibited b y the slower-growing species; (c) one species grew faster than the oth er but with no adverse effects; (d) one species grew faster than the o ther initially, but growth rates of both declined later during interac tion; (e) both species grew at similar rates initially but growth rate of one declined during competition; and (f) both species grew at simi lar rates initially but later reduced the growth of each other. On thi n layers of barley grain, competing species generally showed mutual in hibition on contact, forming discrete colonies whose size was determin ed by the relative radial growth rates of the two species and position s of inocula. However, at 30-degrees, A. flavus overgrew colonies of a ll other species.