Involvement of metabolic components, volatile compounds, PR proteins, and mechanical strengthening in multilayer protection of cucumber plants against Rhizoctonia solani activated by Trichoderma atroviride TRS25.

In the present study, the spread of Rhizoctonia solani-induced disease was limited when cucumber plants were pretreated with Trichoderma atroviride TRS25. The systemic disease suppression was related to TRS25-induced resistance (TISR) induction with simultaneous plant growth promotion. Protection of cucumber was related to enhanced activity of defense enzymes, e.g., guaiacol peroxidase (GPX), syringaldazine peroxidase (SPX), phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO) as well as phenolic (PC) concentration increases in the conditions of hydrogen peroxide (H2O2) accumulation, resulting in thiobarbituric acid reactive substance (TBARS) decrease. Moreover, the obtained results indicated that TISR might depend on accumulation of salicylic acid derivatives, that is methyl salicylate (MeSA), ethylhexyl salicylate (EHS), salicylic acid glucosylated conjugates (SAGC), and ß-cyclocitral as well as volatile organic compounds (VOC) such as Z-3-hexanal, Z-3-hexenol, and E-2-hexenal. The results point to important, not previously documented, roles of these VOC in TISR signaling with up-regulation of PR1 and PR5 gene characteristic of systemic acquired resistance (SAR) and of PR4 gene, marker of induced systemic resistance (ISR). The study established that TRS25 enhanced deposition of callose and lignin in specialized plant cells, which protected vascular system in cucumber shoots and roots as well as assimilation cells and dermal tissues in shoots and leaves. These compounds protected cucumber organs against R. solani influence and made them more flexible and resilient, which contributed to better nutrition and hydration of plants. The growth promotion coupled with systemic mobilization of biochemical and mechanical strengthening might be involved in multilayer protection of cucumber against R. solani activated by TRS25.

Suppression of Rhizoctonia solani in Potting Mixtures Amended with Compost Made from Organic Household Waste.

ABSTRACT Compost made from organic household and garden waste was used to substitute part of the peat in potting mixtures used for growing woody ornamental nursery stock. The effects of amendment with compost on the colonization of potting mixture by Rhizoctonia solani (AG1) were studied in greenhouse experiments. A bioassay was developed using cucumber as a sensitive herbaceous test plant as a substitute for woody ornamental cuttings. Pathogen growth in the potting mixture was estimated by measuring the distance over which damping-off of seedlings occurred. Compost from two commercial composting facilities suppressed growth of R. solani in potting mixtures with 20% of the product when the compost was fresh (directly after delivery) or long matured (after 5 to 7 months of additional curing). In contrast, short-matured compost (1 month of additional curing) from the same batches stimulated pathogen growth. In vitro mycelial growth of R. solani on mixtures with mature compost was inhibited by microbial antagonism. Compost-amended potting mixtures responded differentially to the addition of cellulose powder; the effect on suppressiveness depended on curing time and origin of the compost. In long-matured compost, suppressiveness to R. solani was associated with high population densities of cellulolytic and oligotrophic actinomycetes. The ratio of the population density of actinomycetes to that of other bacteria was around 200-fold higher in mature suppressive compost than in conducive compost.