Response of different forms of propagules of Rhizoctonia solani AG2‐1 (ZG5) exposed to the volatiles produced in soil amended with green manures

Abstract

The sensitivity of different forms of propagules of Rhizoctonia solani anastomosis group (AG)2-1/zymogram group (ZG)5 to volatile compounds produced in soil amended with green manure will influence the efficacy of green manures used to manage the disease. In laboratory experiments, we determined the impact of volatiles arising from residues of five species of Brassicaceae, and Avena sativa (oat), a non-Brassicaceae species, and volatiles of pure allyl isothiocyanate (AITC) or 2-phenylethyl isothiocyanate (2-PEITC) in either their soluble or vapour phase on the hyphal growth of R. solani arising from different propagules. The brassicaceous species were Brassica napus var. Karoo, B. napus B1, B. napus B2, B. nigra and Diplotaxis tenuifolia (a brassicaceous weed). Colony growth and hyphal density on water agar were measured up to 7 days. The amendment of a sandy soil with green manures at a high (100 g kg 21 , 10%) concentration generally suppressed the growth of the pathogen, but at a low (10 g kg 21 , 1%) concentration, the amendment had little effect on the radial fungal growth of the pathogen but increased the density of hyphae through more branching. The inhibition by volatiles from the residues of Brassicaceae species at 10% concentration was stronger (82-86%) than that by volatiles from oat (64%) amendment at the same rate. Hyphae arising from sclerotia and precolonised ryegrass seed were less sensitive than hyphae growing out of potato dextrose agar plugs. This indicates that thickpigmented cell walls may have protected the fungus from these unfavourable conditions. Pure AITC and 2-PEITC in the range of 0.5-2.0 mM inhibited the growth of R. solani from all forms of propagules, but hyphae originating from agar plugs were the most vulnerable compared with the two others. Thus, hyphae arising from the medulla of the sclerotia may be relatively tolerant to volatile compounds emanating from decomposing Brassica green manure amendments in the field and in vitro inhibition of the vegetative growth of the pathogen may not reflect its response to the amendments in the field.

Biofumigation for Plant Disease Control – from the Fundamentals to the Farming System

“…Thick-walled oospores or chlamydospores of various oomyces, or sclerotia of Rhizoctonia and Sclerotinia may be less sensitive to ITCs than germinating propagules of Aphanomyces euteiches or Fusarium oxysporum (Smolinska & Horbowicz, 1999). Recent studies also demonstrated that hyphae of Rhizoctonia solani arising from sclerotia were more resistant to ITCs than those arising from agar plugs (Yulianti et al, 2006). Disease control arising from direct ITC-related suppression may be expected to be more effective for obligate parasites such as that reported for the take-all fungus (Gaeumannomyces tritici) and powdery scab in potato (Spongospora subterranea) where inoculum recovery requires a host, and more variable for saprophytes such as Rhizoctonia solani.…”

Mechanism of Action and Efficacy of Seed Meal-Induced Pathogen Suppression Differ in a Brassicaceae Species and Time-Dependent Manner

“…Amendment rates employed in this and previous studies (10,11,24,25) are equivalent to the application of seed meal at 8 to 10 t ha -1 . These rates equate to an amount that ranges from <1 to 25% of that recently used in the evaluation of composts in greenhouse, apple orchard, and other field-level production systems (5,33,36,37). Seed meal sourced from the same Brassica sp.…”

“…In the current study, capacity of each Brassicaceae seed meal examined to suppress root infection by R. solani AG-5 required activity of the native orchard soil biology. This included B. juncea seed meal, which also produces glucosinolate hydrolysis products previously shown to inhibit this fungal pathogen (18,37), and provide control of damping-off incited by R. solani AG-4 (9). In the case of B. juncea PG, the requirement for an active microbial community and the functional mode of action leading to disease control varied in a temporal manner.…”

Solid-phase micro-extraction (SPME) in the early detection of potentially active volatile compounds from organic wastes used for the management of soil-borne pathogens

“…[15] Nevertheless, no extensive research has been developed to unravel the chemical nature of the volatile compounds responsible for the beneficial effects of biodisinfestation practices. Yulianti et al, [16] in experiments on the simultaneous use of a polyethylene sheet on soil (solarization or biosolarization) to retain the volatiles, highlighted the importance of sulphur compounds released from decaying Cruciferae and Compositae plants for controlling some soil pathogens. Biosolarization usually leads to a considerable enhancement of the organic matter biocidal effect on the soil pathogens, through increased topsoil temperature and concentration of bioactive compounds.…”