A bioassay to compare the disease suppressive capacity of pasture soils

Abstract

Dynamic pathogen complexes can develop under pastures thereby substantially reducing potential productivity Suppression of such pathogen complexes is therefore of great importance and bioassays can quantify disease suppression in soils This study describes the development of a pasturerelevant system Rhizoctonia solani AG 21 induced dampingoff (wirestem) of kale (Brassica oleracea) As kale is not a component of traditional ryegrass clover pasture swards the assay allows assessment of general disease suppression considered more enduring in multiplehostmultiplepathogen systems A pathogenic Rhizoctonia solani isolate was obtained from New Zealand pastoral soil Inoculation of soils with this isolate resulted in a level of dampingoff disease comparable to that induced by reference Rhizoctonia solani isolate Rs0432 Significantly different levels of inoculuminduced disease incidence and progression were found in four distinct pastoral soils In combination with soil physicochemical data and environmental DNA approaches this bioassay can be used to further advance understanding of the influence of farm management practices on disease suppression in pasture soils

Impacts of long-term plant residue management on soil organic matter quality, Pseudomonas community structure and disease suppressiveness

“…The disease suppressive capacity of soils was assessed by measuring incidence and progression of Rhizoctonia solani AG2-1 induced damping-off of kale (Brassica oleracea cv. Caledonian), as described in Dignam et al (2015). Briefly, kale seeds were sown into 7 × 7 × 8 cm pots (with sealed bases) containing 190 g of field-moist soil.…”

“…As a measure of disease progression, the area under the disease progress curve (AUDPC) was calculated, for each pot, from the percentage of plants with damping-off disease (two-day intervals) over the duration of the assay. Following disease assessment, fungal pathogens were isolated from the lesions of diseased plants and identified as described by Dignam et al (2015).…”

“…Compared to the uninoculated soil, disease incidence and progression were significantly higher in inoculated soil for each of the field treatments. Causative agents were isolated from the lesions of both control and inoculated plants, and characterised by microscopy and sequencing of the ITS1-5.8S-ITS2 region (Dignam et al, 2015). DNA analysis of the fungi isolated from the lesions of uninoculated plants identified common soilborne fungal species including Trichoderma harzianum, Fusarium oxysporum, and Boeremia exigua, in addition to Rhizoctonia solani.…”

“…Phylogenetic community analysis using the Illumina MiSeq platform targeted Pseudomonas spp., and a bioassay for disease suppressiveness was applied to the pasture soils utilising a broad-range plant pathogen (R. solani AG2-1) and non-pasture host (kale; Brassica oleracea). Measuring disease incidence on host plants unrelated to the pasture system's current crop species is likely to provide a better comparative measure of general, rather than specific, suppression between the field treatments (Dignam et al, 2015).…”