Dissemination of Verticillium albo-atrum through the Atmosphere

Abstract

IT is usually considered that spread of disease due to Verticillium albo-atrum is either by growth of the pathogen from diseased to healthy susceptible plants by root contact or by the dissemination of infected plant material such as leaves, root stocks, etc. However, the possibility, in some cases, of the disease being spread by airblown spores became apparent when Isaac1 trapped colonies of V. albo-atrum on Petri-dish plates of Dox's agar exposed approximately 2 ft. above a stand of lucerne infected with this pathogen, and also when Davies (unpublished results) isolated V. albo-atrum from house dust from Edinburgh and from the atmosphere in a garden in urban London. It should be pointed out that in diseased lucerne plants, even when they are still alive and green, the fungus grows from the vascular tract in the lower basal regions of the stems out into the cortical tissue and from there superficial hyphae bearing conidia develop; and it has been shown by Isaac that these conidia will cause infection when placed upon recently cut surfaces of mown, healthy lucerne.