Cotton Seedlings by Rhizoctonia solani

HOWELL, C. R. 1978. Seed treatment with L-sorbose to control damping-off of cotton seedlings by Rhizoctonia solani. Phytopathology 68:1096-1098. The keto sugar, L-sorbose, inhibits hyphal extension and accumulate in the soil. When applied to seed in crystalline promotes profuse branching in Rhizoctonia solani. When form with sticker, L-sorbose is highly water soluble and may applied to cotton seed planted in soil infested with the be leached from the spermosphere. Use of a less soluble pathogen, L-sorbose protected the seed against damping-off. formulation consisting of L-sorbose mixed with cellulose It is fungistatic and not fungicidal. Because L-sorbose is acetate in acetone alleviated this problem. metabolized by soil microorganisms, it does not persist or Additional key words: Gossypium hirsutum, emergence, survival. The keto sugar, L-sorbose, first was reported to be a methyl cellulose sticker alone were planted in flats of R. fungus growth inhibitor by Barnett and Lilly in 1951 (1). solani infested or noninfested soil and placed in a growth Subsequently, L-sorbose has been used by a number of chamber set for 14-hr days and 10-hr nights at 22 C. Each investigators to retard hyphal extension in fungi (2, 5, 7). treatment consisted of 30 seeds. Flats were watered daily The mechanism of L-sorbose inhibition appears to be with 800 ml distilled water per flat and incubated for 14 interference with oligosaccharide formation (8) and thus days. Counts were made of preand postemergence disruption of cell wall synthesis in sensitive fungi (3). damped-off seedlings and of healthy survivors. Rhizoctonia solani Kiihn, an important pathogen of Seeds also were coated with a mixture of 10% Lcotton seedlings that can grow through the soil to reach its sorbose and 5% cellulose acetate in acetone (0.1 ml/ seed) host, is sensitive to L-sorbose (7). and air dried. Seeds treated with L-sorbose and cellulose The purpose of this study was to determine the efficacy acetate or cellulose acetate alone were planted in flats of of L-sorbose as a seed treatment to inhibit the growth of soil infested with R. solani or noninfested soil and R. solani in the soil near developing cotton seedlings, compared with seed coated with sorbose by the methyl cellulose method. They were treated the same as in the MATERIALS AND METHODS first growth chamber test, except that the flats were watered with 1,200 ml per flat. Infected and healthy seeds Inoculum.-Sand cornmeal cultures of R. solani and seedlings were recovered from infested soil and prepared according to Papavizas and Ayers (6) were surface sterilized by washing them for 30-sec intervals in incubated at room temperature for 3 wk and then 1% sodium hypochlorite, 70% ethanol, and sterile water. incorporated into nonsterile soil taken from a cotton field Sections were plated on 2% water agar and examined at a rate of 100 g per 12 liters of soil. The inoculum level of after 24 and 48 hr for evidence of mycelial growth. R. solani in the soil after incorporation was determined Inhibitory effect and persistence of L-sorbose in according to the method of Weinhold (10). soil.-The L-sorbose was mixed into moist, nonsterile Seed treatment.-Cottonseed (Gossypium hirsutum L. soil at a concentration of 1% (w/w), and 100-g samples 'Deltapine-16'), were coated with methyl cellulose sticker were packed into 9-cm-diameter glass petri dishes. in water and 0, 5, 10, or 20 mg of crystalline L-sorbose per Controls consisted of moist, nonsterile soil without Lseed. For each treatment 30 seeds were planted sorbose added. Five seeds were planted in each plate at individually in 18 X 150-mm capped culture tubes points equidistant from each other. The soil plates were containing 10 g of moist soil infested with R. solani. The incubated at 22 C for 8 days. At the start of the soil tubes were incubated in the dark at 22 C for 10 days, experiment, and at 2-day intervals thereafter, 0.2-cc soil then harvested and the number of emerged seedlings was plugs were removed from around the seeds. One set of recorded. plugs was placed in metal cylinders on the surface of soil Seeds treated with L-sorbose at 10 mg/seed or with extract agar (the filtrate of autoclaved soil and an equal volume of distilled water with 2% agar added). Sterile 00032-949X/78/o0o 192$03.0o/o water (0.05 ml) was added to each cylinder and the agar Copyright © 1978 The American Phytopathological Society, 3340 surface between the cylinders was inoculated with PDA Pilot Knob Road, St. Paul, MN 55121. All rights reserved, plugs of R. solani. The plates were incubated at 24 C and