The Effect of Fungicides on the Microbial Balance in the Phyllosphere1

Abstract

The sensitivity to fungicides of saprophytic fungi colonizing cereal leaves (mainly ←pink→ yeasts, Sporobolomyces spp.; ← white → yeasts, Cryptococcus spp.; Aureobasidium pullulans and Cladosporium spp.) is discussed. Fungicides like dithiocarbamates, captafol, benzimidazoles and tridemorph reduce the saprophytic microflora, while others have little or no effect. The fungicides are mostly effective for 2–3 weeks after the treatment. When evaluating the consequences of a disturbance of the microbial balance we should realize that the saprophytes are able to antagonize a number of necrotrophic pathogens of cereal leaves and ears (Cochliobolus sativus, Septoria nodorum, Fusarium culmorum, Pseudocercosporella herpotrichoides, Colletotrichum graminicola). This antagonism is based on nutrient competition, which reduces the superficial development of the pathogen before penetration, resulting in a reduction of infection of about 50 % or more. This interaction seems particularly important when saprophytes compete successfully for extraneous nutrients from pollen grains or aphid honeydew, which will otherwise stimulate infection.

Fungicide Effects on Fungal Community Composition in the Wheat Phyllosphere

“…Of these six, five were identified as basidiomycete yeasts (OTU_0_ Sporobolomyces _ roseus , OTU_3_ Dioszegia _ fristingensis , OTU_4_ Cryptococcus _ tephrensis , OTU_12_ Cryptococcus _sp and OTU_9_ Dioszegia _ hungarica ), and one as the ascomycete OTU_5_ Cladosporium _spp. The phyllosphere fungal community of wheat has often been described as consisting of ‘pink’ yeasts ( Sporobolomyces and Rhodotorula producing carotenoid pigments), ‘white’ yeasts ( Cryptococcus ) and ascomycete saprotrophs such as Cladosporium and Alternaria [17], [18]. We were able to confirm the presence of these fungal taxa previously identified by culture-dependent methods (Table 2).…”

Interaction between phyllosphere yeasts, aphid honeydew and fungicide effectiveness in wheat under field conditions

“…a/,, 1991b). Neither prochloraz nor triadimenol had an effect on yeasts, in accordance with the findings of Magan & Lacey (1986) and Fokkema & De Nooij (1981). The maximum yeast population density was higher in the mildew-infected experiments at 'Droevendaal', as was found by Last (1970).…”

Susceptibility of oat cultivars to groat discoloration: causes and remedies

“…The ineffectiveness of the fungicides, especially where a trend towards increased pathogen infection occurred, may be partly attributable to reduction of the natural saprophytic microflora of the leaf surface, such as various yeasts, which normally antagonize necrotrophic pathogens of cereal leaves and ears (Dickinson 1973, Fokkema and De Nooij 1981, Culshaw et al 1988. Attempts to control ÔblackpointÕ on wheat with fungicides have sometimes led to large increases in (Ellis et al 1996).…”

“…Fungicides: Fungicide active ingredients were chosen based on their efficacy on wheat for controlling Alternaria, Microdochium and Fusarium species (Magan and Lacey 1986, Wainwright et al 1992, Milus and Parsons 1994, Liggitt 1997 with due regard for fungicides that may even exacerbate the problem (Culshaw et al 1988, Fokkema and De Nooij 1981, Dickinson 1973.…”