Impact of environmental factors on fungal respiration and dry matter losses in wheat straw

An automatic electrolytic respirometer enabled replicated determinations of the respiration rates of individual fungi on sterile straw, and the mixed mycoflora of naturally contaminated wheat straw at different steady-state t emperatures (10-30 degreesC) and water activities (a(w), 0.75-0.98) over pe riods of 8-14 days. Generally, the respiratory activity of individual spoil age fungi (Alternaria alternata, Cladosporium cladosporioides, Eurotium ams telodami, Fusarium culmorum and Penicillium aurantiogriseum) on sterile whe at straw increased linearly with increasing a(w) at 25 degreesC. The calcul ated maximum dry matter loss of wheat straw due to colonisation by individu al species was about 10%, regardless of a(w). On naturally contaminated whe at straw fungal activity was also related to temperature and a(w), with max imum respiration at 30 degreesC and 0.98 a(w). At the lowest temperature ex amined, 10 degreesC, there was a slight lag prior to respiratory activity o ccurring. The respiratory activity was also significantly reduced (by half) when available water was reduced to 0.95-0.90 a(w). In contrast to the col onisation of sterile straw by individual species, the maximum dry matter lo ss caused by fungal deterioration of naturally contaminated wheat straw was 3.4% at 0.98 a(w) and 30 degreesC. The dominant fungal genera and species varied with a(w) and temperature. These results are discussed in relation t o the storage of cereal straw without spoilage. (C) 2000 Elsevier Science L td. All rights reserved.