Cellulose-decomposing fungi in polder soils and their possible influence on pathogenic fungi

For a study of the colonisation of the IJsselmeerpolders by fungi, attention was fixed on the cellulose-decomposing fungi, since these are considered to represent the more stable part of the mycoflora of soils. If one assumes that in the North East Polder, cultivated for approximately 25 years, the fungal population is approaching stability, the progress of colonisation of the younger polders can be judged by comparison of the number of species found and their frequency.It is shown that the progress of fungal colonisation did not depend only on the time during which a soil has been dry, but also on the use that has been made of it. Of the species known as antagonists of other fungi,Trichoderma spp. provided an increasingly larger proportion of the total population as the soils were further from stability.It is concluded that the increase of fungal antagonists may well be one of the causes of the decline of such parasites asOphiobolus graminis andRhizoctonia solani. Special mention is made ofGliocladium roseum, the parasitism of which towardsR. solani could be demonstrated in paired cultures.