The effects of temperature and water availability on growth and
interactions between fumonisin-producing isolates of Fusarium
moniliforme and F. proliferatum and seven other fungi from
maize grain were determined in vitro. The type of interaction
and index of
dominance (ID) between species were markedly influenced
by temperature and aw. Generally, F. moniliforme
and F. proliferatum were
very competitive and dominant against the Penicillium spp. and
A. flavus. They were in turn dominated by A. niger, but
mutually
antagonistic when paired with F. graminearum and A. ochraceus.
Under slightly drier conditions (<0·98 aw)
A. ochraceus became more
competitive and dominant over the fumonisin-producing species. A. flavus
was dominant only at 30°C and <0·96 aw.
F. moniliforme
and F. proliferatum demonstrated dominance against all species
over a range of temperatures and 0·994 to
0·96 aw. At lower aw levels
they were less competitive. The growth rate of the two
fumonisin-producing species was significantly reduced by F. graminearum,
regardless of aw. F. moniliforme and
F. proliferatum reduced growth of Penicillium and
Aspergillus spp., especially at >0·96 aw.
At
<0·96 aw, growth of these species was unaffected.
Using Biolog plates the effect of aw and temperature
on utilization patterns of
carbon sources in maize were evaluated for the first time. The niche
overlap indices relative to F. moniliforme and F. proliferatum
were
determined and compared with that of each interacting species. NOIs for
F. moniliforme and F. proliferatum were >0·90
at
>0·96 aw
and 25 and 30°, indicative of co-existence with other species.
Most of species had NOIs >0·90, except in some cases when paired
with F. moniliforme, where NOIs <0·80 suggested the
occupation of different niches. Although there was no significant correlation
between the ID and NOI methods both suggested that the niche overlap
between species was in a state of flux and significantly
influenced by both temperature and water availability. This suggests
that interpretation of ID, or NOIs carried out under
one set of
environmental conditions may be misleading when considering interactions
between species and also where screening for biocontrol
potential is being considered.