Cellulose-rich amendments of arable soils do stimulate saprotrophic fungi which may increase competitive suppression of root-infecting fungal pathogen. However, fungal pathogens with a good ability to degrade cellulose may be stimulated by such amendments and increase their disease pressure. The current study explores these possibilities for the notorious fungal pathogen Rhizoctonia solani. First, we determined the growth of R. solani on woody substrates and paper pulp in a Petri dish assay. This revealed that paper pulp is highly supporting growth of R. solani whereas growth on wood sawdusts varied between tree species, with lowest biomass production on coniferous wood sawdust. A sub-set of the materials used for the growth test was mixed with Rhizoctonia-infested soil and after two weeks of pre-incubation fungal biomass was determined and red beet seeds were sown. Oak-, elder sawdust and paper pulp decreased the disease incidence of red beet seedlings, which was accompanied by fungal biomass stimulation in soil. The same infested soil was used to test the timing of the soil amendment with respect to that of sowing. For this timing experiment not only cellulose-rich amendments were used but also hair meal and shrimp meal, organic amendments that have received attention for disease suppressing effects. A short time interval (1 day) between soil paper pulp amendment and sowing resulted in a clear increase of disease of red beet seedlings. This coincided with an increase R. solani in soil and roots as based on qPCR. Amendments with sawdusts, shrimp- and hair meal did not have these effects. An interval of 2 weeks or longer between paper pulp addition and sowing resulted in disease suppression. Oak sawdust amendment, showed the strongest disease suppression independently of the time interval between amendment and sowing. Our results indicate that investigations of effects of soil organic amendments on growth- dynamics of saprotrophic fungi and soil-borne pathogenic fungi can be helpful to develop successful sustainable disease-suppressing strategies.
|Date made available||9 Jun 2021|