Fusaria and Fusarium mycotoxins in leaves and ears of maize plants 2.: A time course study made in the Waikato region, New Zealand, in 1997

The patterns of fungal infection and mycotoxin contamination in leaf and ear sections of plants of two maize (Zea mays L.) hybrids, one resistant to mycotoxin accumulation under New Zealand conditions (Pioneer 3902 (P3902)) and one less so (Pioneer 3751 (P3751)), have been measured. Sampling commenced early in the season, well before ear and tassel formation, and continued until harvest. A number of fungi were isolated, the most common overall being Fusarium. Most common in leaf fractions were Epicoccum, Fusarium, and Alternaria, whereas in ear fractions the most common were Fusarium, Penicillium, Cladosporium, and Mucor. The most common fusaria isolated from leaf fractions were the toxigenic species F. crookwellense and F. graminearum. These species were evident from late February although other, non-toxigenic, species were present in leaf axils from early January. For ear fractions the most common species were F. graminearum, F. crookwellense, and F. subglutinans. Fusarium infection was evident in ears of P3902 from March to April, although heavy infection by the toxigenic species tended to occur later towards May-June, especially for the basal ear fractions. For P3751 ear infection commenced in May, and then was predominantly by toxigenic species. Mycotoxins were found in most plant fractions measured, especially as the plants aged. The toxins found reflected the particular toxigenic Fusarium species present in the fraction. The highest mycotoxin concentration in a leaf fraction was 16.6 mg/ kg of zearalenone (ZEN) in an upper leaf axil sample. Nivalenol (NIV) was also found at up to 7.4 mg/ kg in leaf axils. The most contaminated ear fraction was the rachis, with over 40-95 mg/kg of ZEN, NIV, or deoxynivalenol (DON) at various times. The highest concentration found in kernels was 3.8 mg/kg of DON found in apical kernels of P3751 two weeks before harvest. The results suggest that the mechanisms of maize infection by Fusarium in New Zealand may not be controlled by factors at silk emergence but rather by later season events such as high rainfall and warmer temperatures.