AN ULTRASTRUCTURAL-STUDY OF TOMATO ROOTS INOCULATED WITH PATHOGENIC AND NONPATHOGENIC NECROTROPHIC FUNGI AND A SAPROPHYTIC FUNGUS

Tomato cultivar Moneymaker was independently inoculated with Alternari a alternata, Cunninghamella elegans, Fusarium culmorum, F. oxysporum f .sp. lycopersici, F. oxysporum f.sp. pisi and Stromatinia gladioli and analysed ultrastructurally. The extent and amount of superficial fung al growth on tomato roots was similar but C. elegans, a saprophyte, wa s exceptional in that hyphae were not closely appressed to plant surfa ces and did not adhere to plant cell walls. In general, the type of pl ant responses to fungal colonization and infection were similar in all of the interactions studied, with the exception of C. elegans which d id not infect tomato root tissue. The failure to penetrate tomato root s by C. elegans may have been associated with the lack of hyphal adhes ion to plant cell walls. Migration of cytoplasm and wall apposition/pe netration papilla formation were regularly observed in tomato root tis sue beneath appressed hyphae and at sites of fungal infection. Specifi c cellular reactions in the exodermis, namely the formation of wall 'i nclusions' and appearance of 'sensitive' cells, indicated that exoderm al cells were particularly responsive to fungal challenge. Fusarium ox ysporum fsp. lycopersici, a pathogen of tomato, invaded tomato root ti ssue more extensively than the other fungi inoculated onto tomato root s. Infection of tomato by the other fungi studied was variable, and th e extent and success of fungal invasion was tentatively associated wit h their necrotrophic capability and typical host range.