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Sites of Infection of Fusarium oxysporum f. pisi Race 5 on Peas. Robert F. Nyvall, Department of Plant Pathology, Washington State University, Northwestern Washington Research and Extension Unit, Mount Vernon, Washington 98273, Present address of senior author: 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, Washington 98273. Phytopathology 62:1419-1424. Accepted for publication 26 June 1972. DOI: 10.1094/Phyto-62-1419.

Propagules of Fusarium oxysporum f. sp. pisi race 5 initially infect pea cotyledons, but independent infections of roots must occur for plants to exhibit severe wilt symptoms. In 7-14 days, other soil fungi such as F. solani, F. roseum, and F. oxysporum types, nonpathogenic to peas, colonize both cotyledons and roots as secondary invaders. Infection by race 5 at a single site on one root may kill a pea plant before maturity, but severity of symptoms is directly proportional to the number of infection sites. Race 5 infects through wounds or penetrates directly through the epidermis.