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Association of Virus-Induced Changes in Laimosphere Microflora and Hypocotyl Exudation with Protection to Fusarium Stem Rot. A. C. Magyarosy, Former Research Assistant, Department of Plant Pathology, University of California, Berkeley 94720, Present address of senior author: United States Department of Agriculture, Salinas, California 93901; J. G. Hancock, Associate Professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 64:994-1000. Accepted for publication 14 February 1974. DOI: 10.1094/Phyto-64-994.

Microbial populations were 2- to 7-fold higher in soil surrounding (0-3 mm) hypocotyls (laimosphere) of squash mosaic virus-infected squash (Cucurbita maxima) plants than healthy ones, and virus infection stimulated an increase (approx. 40%) in hypocotyl exudation. However, hypocotyl penetration by Fusarium solani f. sp. cucurbitae and initial lesion development were not influenced by virus infection. Yet protection to Fusarium stem rot was induced by squash mosaic and was expressed if the inoculum was in soil. Protection was overcome at higher fungal inoculum levels. The influence of squash mosaic on the laimosphere microflora and the regulation of protection by Fusarium inoculum levels in soil supports evidence that virus-induced resistance to stem rot is expressed during the prepenetration phase of pathogenesis. There were no differences in the rates of permeation of urea across hypocotyl cell membranes in healthy or squash mosaic virus-infected squash plants. Furthermore, virus infection had no influence on the rate of uptake of 3-o-methylglucose, 2-aminoisobutyrate, glucose, alanine, glutamate, leucine, glycolate and malate by hypocotyl tissues. Apparently changes in membrane permeability or the activity of certain membrane transport systems do not account for hypocotyl exudation increases associated with squash mosaic.

Additional keywords: permeability, membrane transport.