Interactions between field, and storage fungi on wheat grain

Abstract

The effects of different water activities (aw) and temperatures on interaction between groups of field fungi, Aspergillus and Penicillium spp. on wheat grain were measured using direct and dilution plating. Numbers of individual species isolated and the percentage of grain contaminated changed considerably during a four week incubation period. At the end of this period, the relative abundance of each species did not correspond well with that predicted using a numerical Index of Dominance (ID) derived from studies in vitro. When wheat grains were inoculated with different field fungi and incubated for four weeks, Fusarium culmorum became dominant and contaminated most grains at all temperatures (15–30 °C) and 0 · 99 and 0 · 95 aws although the in vitro ID was large only at 15°. Epicoccum nigrum, which had a high in vitro ID at all temperatures, did not compete well on wheat grain at any temperature, while Alternaria alternata which had a low ID, contaminated up to 50% grain after four weeks storage. Of the Aspergillus spp., A. versicolor was dominant at all temperatures and aws tested (0 · 95 and 0 · 90) although it competed poorly in culture. A. repens and A. candidus were also present at 15° and A. nidulans at 25–30† and 0 · 95–0 · 90 aw. The dominance of Penicillium hordei on wheat grain corresponded well with its ID at 15–25° and 0 · 95 aw but less well at 0 · 90 aw. P. piceum was seldom isolated at 15° but was most numerous at 30°. P. verrucosum var. cyclopium (P. aurantiogriseum) and P. brevicompactum competed well at 15–25° and 0 · 95–0 · 90 aw. When groups of Aspergillus and Penicillium spp. were inoculated together on wheat grain, A. versicolor and P. hordei became dominant at 15–25° and 0 · 95 and 0 · 90 aw, while at 30° A. nidulans and A. repens were also numerous.