Mechanisms of a container medium for suppression of Rhizoctonia damping-off of cabbage seedlings
Mechanisms of a container medium for suppression of Rhizoctonia damping-off of cabbage seedlingsJW HUANGlDepartment of Plant Pathology, National Chung Hsing University, Taichung, Taiwan
Background and objectivesComposted agricultural wastes have shown considerable promise as container media and soil amendments to control soilborne plant pathogens[1,21. The materials used include crop debris , tree bark , and cattle manure. The proposed study is a novel approach to explore the mechanisms of a container medium formulated with agricultural wastes for suppression of damping-off pathogens.
Results and conclusionsEight agriculture wastes including spent forest mushroom compost (SFMC), spent golden mushroom compost (SGMC), rice hull, carbonized rice hull, peanut husk, coconut fiber, bagasse meal, wasted cotton, etc. were evaluated for effects on the growth of cabbage seedlings. Among them, SFMC and SGMC Nvere the most suitable growth substrates for cabbage seedlings and, thus, the potential media for replacement of BVB No.4 peat moss which is used in container crops. Growth of cabbage seedlings was markedly affected by composting period of SFMC and SGMC, the longer the composting period, the stronger seedling vigor. The optimum composting period for SFMC and SGMC was 12 and 6 weeks, respectively. A container medium (SSC -06 medium) was formulated with SFMC, carbonized rice hull, shrimp & crab shell powder, blood waste, and lime. The SSC -06 medium was suitable for growth of cabbage seedlings and able to markedly inhibit colonization of cabbage seed by Rhizoctonia solaniAG-4 and significantly reduce damping-off severity of the seedlings caused by the pathogen after it was made, and then aged for more than 10 days at 24-28 'C. Suppressive effect of 20-day-old SSC -06 medium on seed colonization by R. solani AG-4 was partially nullified after it was steamed by 100 'C - hot air for 15 -3 0 min. However, the inhibitory effect was immediately restored to steamed SSC -06 medium after infestation with Trichoderma harzianum (TH-05) at concentration of 105 cfu/g dry medium. Population densities of bacteria and fungi in SSC -06 medimn steamed at 100 'C for 0, 5, 10, 15, 25, and 30 min. were detected by peptonedextrose-rose bengal agar medium (PDRA) and nutrient agar medium (NA), respectively. After the medium was steamed for 5 -30 min., no fungal colonies were observed on PDRA plates, but the colony-forming units of bacterial population were maintained at 106/g dry medium on NA plates. It is suggested that T. harzianum and other fungi are involved in the suppressiveness of SSC -06 medium to R. solani AG-4.
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