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Stunting of Citrus Seedlings in Fumigated Nursery Soils Related to the Absence of Endomycorrhizae. G. D. Kleinschmidt, Graduate Teaching Assistant, Department of Plant Pathology, University of Illinois, Urbana 61801, Present address of senior author: Cooperative Extension, Service P.O. Box 1117, Presque Isle, Maine 04769; J. W. Gerdemann, Professor, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 62:1447-1453. Accepted for publication 3 July 1972. DOI: 10.1094/Phyto-62-1447.

Stunted and chlorotic citrus seedlings growing in fumigated nurseries in California and Florida were nonmycorrhizal, and Endogone spores were not found associated with their roots; whereas seedlings growing normally in scattered areas of these nurseries were mycorrhizal, and Endogone spores were present. Stunted plants from nurseries grew normally after inoculation with Endogone mosseae, an endomycorrhizal fungus. Noninoculated citrus seedlings grew poorly in steamed, autoclaved, or methyl-bromide-treated soil in greenhouse experiments. Plants inoculated with E. mosseae produced excellent growth in these treated soils. Inoculation also improved the growth of citrus seedlings in an Illinois field plot that had been fumigated with methyl bromide. All mycorrhizal plants had a greater dry weight and a higher percentage of phosphorus than did nonmycorrhizal plants. Stunting and chlorosis of citrus in fumigated or heat-treated soils have been previously attributed to soil toxicity. Our evidence indicates that the major cause of this problem is inadequate nutrition brought about by the killing of mycorrhizal fungi.

Additional keywords: vesicular-arbuscular.