In a survey of the incidence of Fusarium species on plants from cereal, fungicide- trial plots in the east o f Scotland, carried out in 1987 and 1988, F. culmorum was the most prevalent pathogenic species and F. dimerum the most frequently occurring saprophyte. The form er species was generally distributed over roots, stems and ears but F. dimerum was confined to roots and stems. High infection levels o f other pathogens, F. avenaceum and F. nivale, and o f the weak pathogens, F. poae and F. sambucinum, were found only sporadically. Fusariumspecies occurring in slight or traces amounts included, F. graminearum, F.moniliforme, recognized pathogens o f cereals, F. equiseti, F. sporotrichioidesand F. tricinctum, weak pathogens, and F. acuminatum, F. oxysporum, F.semitectum, F. solani andF. sulphureum which are non-pathogenic to cereals. Fungal genera, other than Fusarium, which were prevalent included Cylindrocarpon on roots, Mucor on stems and Cladosporium on ears. Trichothecium roseum was frequent in some crops and attracted interest as a potential antagonist o f Fusarium and as a potential plant pathogen. Fungicide treatments applied to plots to control m ainly cereal leaf diseases were found to have a beneficial side effect in often giving a moderate reduction in Fusariuminfection. However, it is suggested that this field exposure o f Fusarium pathogens to fungicides may predispose towards future insensitivity problem s. In vitro tests on the response o f different Fusarium species to triadim enol fungicides showed a greater sensitivity in F. nivale and F. dimerum compared w ith other species which may be linked w ith their distinctive taxonom ic grouping. The low incidence oiF. nivale in the survey relative to that reported by earlier workers may be attributed in part to the more frequent application o f fungicides to cereal crops in the field and the sensitivity o f this fungus to the w idely used triadim enol-
containing form ulations. A further factor accounting for the unexpectedly low incidence o f/7, nivale may have been the relatively m ild winters and warm summers over the period o f this survey which w ould be unfavourable to this low tem perature fungus. From artificial inoculation o f ears o f different cereals with Fusarium species, F. culmorum, followed by F. avenaceum and F. graminearumwere shown to depress grain yield significantly, F. culmorum having a m ajor effect on grain size and the other two species causing a decrease in grain numbers. Earlier inoculations during the flowering period aggravated the effects o f infection. The introduction o f T. roseum 1 week before inoculation reduced these effects. The carry-over o f ear inoculated Fusarium on seed was generally greater w ith the m ore pathogenic species, which also showed m ore deep-seated infection. However, the weak pathogen F. sambucinum also showed a high rate o f carry-over and deeper penetration o f seed tissues. Seed and soil inoculation tests confirm ed th a t/7, culmorum was the most pathogenic species, followed by F.avenaceum and F. graminearum. The addition o f T. roseum to Fusariuminoculum adversely affected seed perform ance but other fungi, an isolate of Penicillium and o f Cladosporium, reduced disease effects.