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Increased Susceptibility to Fusarium Crown and Root Rot in Virus-Infected Asparagus. T. A. Evans, Former graduate assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48825, Present address: Department of Plant Science, University of Delaware, Agricultural Research and Education Center, Georgetown 19947; C. T. Stephens, associate professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48825 Phytopathology 79:253-258. Accepted for publication 5 October 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-253.

Asparagus (Asparagus officinalis L.) seedlings infected with asparagus virus II (AV-II) became significantly more diseased when inoculated with Fusarium oxysporum f. sp. asparagi than did virus-free seedlings. Asparagus seedlings doubly infected with both AV-I and AV-II became more diseased when inoculated with F. o. asparagi than seedlings infected with either virus alone. Increased levels of Fusarium crown and root rot in asparagus infected with either or both viruses were correlated with an increase in root exudation and an increase in susceptibility of root tissues to infection by the pathogen. Root exudates from AV-II-infected asparagus plants grown in liquid culture contained more electrolytes (3), carbohydrates (1.7), and amino acids (8) than those from virus-free plants. Germination and subsequent germ tube growth from conidia of F. o. asparagi was stimulated more by root exudates from virus-infected plants than from virus-free plants. Histopathology studies indicated that virus-infected asparagus seedlings were less able than virus-free plants to wall-off and lignify the infection courts of F. o. asparagi.