Germination of chlamydospores of Fusarium oxysporum f. sp. pisi race 1 in the rhizosphere, and penetration of the pathogen into roots of a susceptible and a resistant pea cultivar

Abstract

Germination of chlamydospores ofFusarium oxysporum f. sp.pisi race 1 in the rhizosphere of pea seedlings and red clover seedlings grown in natural soil heavily infested with the pathogen, was highest in percentage along the actively growing parts of the roots. At these sites, exudation of ninhydrinpositive substances and reducing sugars was most intense with seedlings grown in vitro. No significant difference in the percentage of germinating chlamydospores ofFusarium oxysporum f. sp.pisi race 1 were observed in the rhizosphere soil and on the root surface of homologous parts of roots of seedlings and mature plants of a susceptible ‘Rondo’ and a resistant ‘Rovar’ pea cultivar grown in natural soil heavily infested with the pathogen. Differences in the growth of mycelium of the pathogen on the root surface, or in the attachment of the mycelium to the root surface of both cultivars were not observed. Epidermis and cortex cells of roots of both cultivars reacted on penetration by the pathogen by producing a cellulose thickening of the cell wall, which later became infiltrated with a ligning-like material. A selective effect on the activities of the pathogen in the rhizosphere, on the root surface and in the epidermis and cortex in relation to resistance thus could not be demonstrated. Formation of new chlamydospores from germ tubes of germinating chlamydospores was frequently observed in the rhizosphere of the susceptible and resistant pea cultivar and in the rhizosphere of red clover seedlings.