THE PROTECTIVE EFFECT OF RUST INFECTION AGAINST OZONE, SULFUR-DIOXIDE AND PARAQUAT TOXICITY SYMPTOMS IN BROAD BEAN

A localized but highly protective effect of rust infection towards injury induced by the air pollutants ozone and sulphur dioxide, either alone or in mixture and the herbicide paraquat was found. The effect was proportional to inoculum density, was non-translocatable, and dependent on temperature. Protection continued even after the infection was no longer active, and was induced by different strains of the fungus in cultivars of both broad bean and pea. Protection was not due to the exclusion of pollutants resulting from stomatal closure. Histopathorogical investigations indicated that the effect was present in uncolonized tissues adjacent to the site of infection. Ultrastructural studies showed normal cell structure in the green islands surrounding the infection centres, even when nearby regions had collapsed. Peroxidase activity was increased rapidly in the infected tissues both in the colonized and in the adjacent non-colonized cells. Such activity was not detectable at significant levels in non-parasitized tissues. The results are discussed in connection with the possible mechanisms involved.