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The Effect of Plant Age on Severity of Pea Wilt Caused by Fusarium oxysporum f. sp. pisi Race 5. Robert F. Nyvall, Department of Botany and Plant Pathology, Iowa State University, Ames 50010; William A. Haglund, Department of Plant Pathology, Washington State University, Northwestern Washington Research and Extension Unit, Mount Vernon 98273. Phytopathology 66:1093-1096. Accepted for publication 29 January 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1093.

Peas grown in soil infested with Fusarium oxysporum f. sp. pisi race 5 and transplanted after 3 or 7 days to noninfested soil exhibited mild disease symptoms as measured by plant dry weight. Peas grown 14 or more days in infested soil exhibited severe disease symptoms and usually died within 21 days. Dry weight loss was 57% greater after 14 days in infested soil than after 7 days and 50% greater after 28 days than after 14 days in infested soil. Peas grown 21 or more days in noninfested soil, then transplanted to infested soil or to soil artificially inoculated with chlamydospores exhibited only mild disease symptoms and the fungus was not isolated from the upper portions of the plants. However, peas grown 14 days or less in noninfested soil then transplanted to infested soil developed severe disease symptoms and died. The population of race 5 was highest in the rhizosphere of 14-day-old plants but probably had little effect on disease severity since plants were infested 3 days after sowing. Seven- and 21-day-old plants exposed to infested soil for various time periods and transplanted into noninfested soil exhibited wilt symptoms and these became progressively more severe the longer the plants were exposed to infested soil. Wilt severity is dependent on the age of plants at infection and length of time of root-fungus contact.

Additional keywords: Pisum sativum, soil fungi.