EFFECT OF WATER ACTIVITY AND TEMPERATURE ON COMPETING ABILITIES OF COMMON MAIZE FUNGI

The effect of water activity (a(w), 0.995-.85) and temperature (15, 25 degrees C) on the in vitro inter- and intra-specific interactions bet ween thirteen fungi commonly isolated from maize grain were investigat ed. The fungi were paired and their interactions given a numerical sco re to obtain an Index of Dominance (I,) for each species. Aspergillus niger had the highest overall I, in most of the conditions tested, whi le the Aspergillus species tested were also quite dominant. Fusarium s pecies appeared to be dominant only at high water availability (0.995 a(w)), while Eurotium species dominated at the lower a(w)s (0.85-0.90) . The relative growth rates of each fungus were also calculated under the same range of environmental conditions. In general, Aspergillus, F usarium and Trichoderma species grew most rapidly under the combinatio n of a,, and temperature conditions in which they were able to grow, w hile Penicillium species had the slowest growth rates. There was a pos itive correlation between growth rate and I-D for Trichoderma viride a nd three Fusarium spp. but not for Aspergillus and Penicillium and Eur otium spp. The different possible strategies in fungal competition for grain are discussed in relation to these in vitro findings.