Assessment for animal feed of maize kernels naturally-infected predominantly with Fusarium moniliforme and Diplodia maydis. I. Fungal isolations and changes in chemical composition

Abstract

A study was made of the physical characteristics, fungal associations and the chemical composition of five batches of maize grain (designated A, B, J, M and P) damaged by ear-rot. All batches were the yellow hybrid, Dekalb XL81, except batch A which was a white variety, Dekalb DS456W. Batch A was separated by vibrating gravity grading into heavy (A-H) and light (A-L) fractions. For each batch, kernels were sorted visually into sound and mould-damaged samples to examine for any differences. The proportion of sound kernels in batches A, A-H, A-L, B, J, M and P was 874, 926, 260, 830, 854, 789 and 964 g kg-' respectively. Bulk density (r = 0.98) and 100 seed weight (r = 0.81) were highly correlated (P < 0.01) with the proportion of mould-damaged kernel in the sample. In visually sound kernels, Fusarium monilifome, Acremonium strictum and Penicillium spp. were the most prevalent fungi isolated. In visually damaged kernels, F. moniliforme was the fungus most frequently isolated other than for batch J where D. maydis was equally prevalent. Penicillium spp. and F. subglutinans were found in all batches but at low isolation frequencies. Compared to the respective sample of sound kernel, the content of crude protein and ash was increased and crude fat was decreased by the mould damage (P < 0-05); fibre, though more variable, was generally increased but gross energy was unaffected (P > 0.05). In visually sound kernels, the amounts of threonine, valine and glycine in the protein (g 16gN-1 ) decreased (P < 0.05) with increasing grain N content. In contrast, in visually mould-damaged kernels, lysine increased and histidine and cystine decreased with increasing grain N content (P < 0.05).