Abstract
Nine samples of maize collected from Grain Marketing Board Centres during 1991, and a further 47 samples collected directly from farmers (41) and the G. M. B centres in Chinhoyi and Kwekwe (6) during 1992, were analysed mycologically. The predominat flora was Fusarium, although Penicillium, Nigrospora, Aspergillus and Chaetomium could be isolated from some samples. From a total of 2821 fungal isolates obtained from all the maize samples analyzed, 1485 (53%) were found to belong to the Liseola section of Fusarium. From the first nine samples studied, F moniliforme and F subglutinans were isolated in almost equal numbers on samples from the Central and South of the country. The subsequent study demonstrated that there was a greater fungal diversity in samples from Mashonaland West than samples from the Midlands area with species of Nigrospora, Chaetomium, Acremonium and Diplodia occurring in significant numbers. A total of 886 isolates were obtained from the different samples. These isolates were then used to evaluate the importance of morphological characters, mating groups and mycotoxin production (zearalenone, monilifoimin and fumonisin B1) in delineating taxa in the Liseola section and also to find out any relationship between these characters and the geographical origin of the isolates. Chlamydospore formation, mode of microconidia production, the type of the conidiogenous cell and the shape of the microconidia were found to be very reliable in delineating taxa in this study. A classification scheme based on these characters was formed and used to distinguish the different taxa. Mating tests carried out also supported the stability of the scheme adopted using morphological characters. However, these tests also showed that the success of a cross in this section is highly dependent on the 'sex' of the isolates involved and may be independent of the geographical origin of the isolates Results on mycotoxin production showed that zearalenone production was not common in the Liseola section, moniliformin production was mostly by isolates in groups B1 (= F proliferation), J2 (= F. subglutinans), J3 (= F. anthophilum) and K5 (=F. oxysporum?, F. nygamai?, F. dlamini?), and fuminsin B1 production was mostly by isolates in groups Al (= F moniliforme) and K5. There was no observed From the results of this study, it was proposed that the species in the current sections Liseola, Elegans and Dlaminiela be grouped into one section and be assigned a new name - section Microconidios. Also, a new species, Fusarium microsporus Mubatanhema & Moss, is described, containing two varieties: Fusarium microsporus var monophialidicus Mubatanhema & Moss. Fusarium microsporus var polyphialidicus Mubatanhema & Moss.