Organic matter input influences incidence of root rot caused by Rhizoctonia solani AG8 and microorganisms associated with plant root disease suppression in three Australian agricultural soils

Abstract

Soil-borne plant root disease caused by Rhizoctonia solani AG8 is prevalent in cereal farming systems worldwide, particularly in semiarid agricultural regions. A controlled environment study was undertaken using three Australian soils to test the hypothesis that OM input from crop roots and residues decreases infection by Rhizoctonia root rot via biologically mediated disease suppression. The specific aim was to determine the relative effect of two different OM inputs (wheat stubble or roots) on (a) abundance (DNA) of the pathogen R. solani AG8 and soil organisms putatively associated with disease suppression, and (b) incidence of Rhizoctonia root rot infection of wheat seedlings (% root infected). An increase in microbial biomass carbon (C) following OM amendment indicated a potential for enhanced general biological disease suppression in all soils. OM inputs also increased the population size (DNA) of certain bacteria and fungi putatively associated with specific suppression for Rhizoctonia root rot, suggesting a C resource-mediated change in microbial functions related to disease suppression. There were no significant changes to measured pathogens with stubble addition. However, OM inputs via root residues and rhizodeposits from living roots increased the populations of R. solani AG8 and Gaeumannomyces graminis var. tritici so that in subsequently planted wheat there was greater incidence of root disease infection and reduced plant shoot and root DM compared with that following OM input as stubble. Differences between soils in terms of plant and soil organism responses to each OM input suggest that abiotic factors modify the development of biological disease suppression and the expression of the disease.

Potential for suppression of Rhizoctonia root rot is influenced by nutrient (N and P) and carbon inputs in a highly calcareous coarse-textured topsoil

“…Available C is a key driver for biological activity in soil, and more specifically the effect of OM addition for increased root disease suppression and enhanced beneficial biota is well documented (Alabouvette 1999;Hoitink and Boehm 1999;Bonanomi et al 2018). Indeed, an effect of C inputs on potential for root-disease suppression in the soil used for this study has previously been reported, although other edaphic constraints were still considered to be limiting (Davey et al 2019). Rhizoctonia solani AG8 is known to be highly and competitively saprophytic (Sneh et al 2013), and possibly could access more recalcitrant C sources in the soil OM which might give it an advantage over other microorganisms in a soil where available C is limited.…”

“…Trichoderma) (Kullnig-Gradinger et al 2002;Barnett et al 2006;Ophel-Keller and Barnett 2006;Vinale et al 2008b). These specific organisms were investigated because they had been detected in other agricultural soils from the same region where the soil in this study was collected (Davey 2013) and have been shown to be associated with decreased root infection in wheat in a bioassay (Davey et al 2019).…”

“…Furthermore, although a controlled environment study of three soils from the same region indicated that addition of OM increased the potential for soil-borne root disease suppression by reducing root infection and increasing DNA of potentially suppressive organisms (E. acetylicum, P. agglomerans and Microbacterium and Trichoderma spp. ), the effect was least in the soil that was the most calcareous (Davey et al 2019). This limited disease suppression potential was postulated to be the result of edaphic limitations, in particular low P availability, that reduced both plant and soil organism growth and function despite C inputs.…”

Soil texture, infective juvenile concentration, and soil organic matter influence the efficacy of Steinernema feltiae isolate Lican Ray

“…While several studies have shown the benefits of soil OM on soil inhabitants in general (Hoitink and Boehm, 1999;Davey et al, 2019), few have focused on EPN performance (Kapranas et al, 2017). For instance, Herren et al (2018) observed higher survival and virulence of S. feltiae on larvae of Galleria mellonella (Lepidoptera: Pyralidae) in soils with added mature compost.…”

“…In addition, OM improves soil structure, lowering bulk density, increasing the available space through the distribution of aggregates and pore size, thus OM content and soil compaction may influence EPNs infection patterns ( Kapranas et al, 2017 ), and persistence in the soil ( Shapiro and Lewis, 1999 ). While several studies have shown the benefits of soil OM on soil inhabitants in general ( Hoitink and Boehm, 1999 ; Davey et al, 2019 ), few have focused on EPN performance ( Kapranas et al, 2017 ). For instance, Herren et al (2018) observed higher survival and virulence of S. feltiae on larvae of Galleria mellonella (Lepidoptera: Pyralidae) in soils with added mature compost.…”