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Effect of Soluble Aluminum on Growth and Pathogenicity of Verticillium albo-atrum and Whetzelinia sclerotiorum from Sunflower. R. G. Orellana, Research Plant Pathologist, Applied Plant Pathology Laboratory, U.S. Department of Agriculture, Beltsville, Maryland 20705; C. D. Foy(2), and A. L. Fleming(3). (2)(3)Research Soil Scientist and Chemist, Plant Stress Laboratory, Beltsville Agricultural Research Center, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705. Phytopathology 65:202-205. Accepted for publication 3 September 1974. DOI: 10.1094/Phyto-65-202.

Verticillium albo-atrum from sunflower was nearly suppressed by 8 µg/g Al+3 in vitro and was characterized by hyaline, apparently unpigmented mycelia and few, if any, microsclerotia. This Al-sensitivity was related to the toxicity of soluble Al in the culture substrate at pH 4.7 or below. Whetzelinia sclerotiorum was tolerant to Al because it grew with as much as 32 µg/g Al+3 even though the acidity of the substrate increased to pH 3.7. Sclerotial development was, however, inhibited by Al above 16 µg/g. The Al-sensitive V. albo-atrum was more harmful to sunflower plants grown in acid, Al-toxic Bladen soil amended with 3,000 µg/g CaCO3 (pH 5.4) than with 750 µg/g (pH 4.4). The Al-tolerant W. sclerotiorum was extremely harmful to sunflower plants grown in acid, Al-toxic Tatum soil amended with 750 µg/g CaCO3 (pH 4.4). These host-pathogen interactions might have been influenced by the extent of detoxification of soil Al by CaCO3.

Additional keywords: Sclerotinia sclerotiorum, Verticillium dahliae, fungus physiology.