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Effect of Solar Heating and Soil Amendments of Cruciferous Residues on Fusarium oxysporum f. sp. conglutinans and Other Organisms. J. Ramirez- Villapudua, Professor, Universidad Autonoma de Sinaloa, Mexico; D. E. Munnecke, Professor and Plant pathologist emeritus, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 78:289-295. Accepted for publication 25 August 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-289.

In the laboratory and in pots buried in the field, the severity of cabbage yellows and populations of Fusarium oxysporum f. sp. conglutinans in soils were markedly reduced by amendments of nine cruciferous species; moderately reduced by alfalfa hay; and increased by wheat straw, chicken manure, or steer manure. The effectiveness of a cabbage amendment was increased by drying the residue before incorporation and was directly related to the concentration and time of exposure. Solar heating (full sunlight, polyethylene cover) of pots of soil amended with cabbage residues practically eliminated propagules of F. o. f. sp. conglutinans, and cabbage yellows was undetected in cabbage growing in the soil. The effectiveness of the treatment was complete within the first 15 days. Especially significant is the fact that cruciferous amendments in conjunction with solar heating or shade treatments were far more effective than solar heating or shade treatments alone. In laboratory experiments populations of F. o. f. sp. conglutinans were reduced almost to zero (reduced by 99.4%), total fungi were decreased by about 20%, actinomycetes apparently were unaffected, and bacterial populations were increased 16-fold by gases arising from decomposing cabbage residues in soil in closed containers. The drastic reduction of propagules of F. o. f. sp. conglutinans only occurred in closed containers. In closed jars, the fungus, which had been growing on potato-dextrose agar in petri dishes suspended above soil containing cabbage residues or moistened cabbage alone, ceased growing. The effect was fungistatic, since growth resumed upon transfer of the fungus to fresh potato-dextrose agar. In contrast, when infested soil was suspended above the decomposing cabbage residues, the effect was fungicidal. A growth-promoting effect was observed on cabbage plants grown in soil amended with cabbage residues, but tomato plants wilted within 24 hr after being planted in the amended soil.

Additional keywords: soil bacteria, soil fungi, soil solarization.