A histological study of the pathogenesis ofverticillium dahliaeKleb. in tobacco

Abstract

Histological observations of Verticillium dahliae Kleb. in tobacco are described. The pathogen did not invade the living tissues of the root tip or parenchyma cells of xylem.Systematic invasion of a resistant variety by the pathogen WcS reduced initially by gummosis and secondary proliferation by tylosis. In susceptible plants, although gummosis and tylosis were present, the mechanisms did not completely inhibit spore germination or migration of the pathogen.The number of infected areas in the mid-stem region was less in the resistant than in a susceptible variety. Such infected areas involved only one of two vessels laterally in the former, whereas 3-5 vessels were involved in the latter.Formation of microsclerotia and profuse secondary sporulation were rare. Morphological symptoms in the leaves were always associated with the presence of the fungus nearby.