The role of avenalumin in the resistance of oat to crown rust, Puccinia coronata f. sp. avenae

Abstract

The relationship between the degree of expression of resistance and the production of avenalumins was investigated in the interactions of 2 physiological races of Puccinia coronata avenae and 21 oat Pc lines each carrying a different single major gene for resistance. Avenalumins accumulated in all incompatible interactions. More rapid and abundant accumulation of avenalumins was found in the more incompatible interactions where fungal growth was more rapidly restricted. Large accumulation of avenalumins coincided with the time of detection of retardation of hyphal growth within leaf tissues. Very little accumulation of avenalumins was found in any compatible interaction. Investigations with the incompatible Shokan 1-race 226 combination showed that the amount of accumulated avenalumins was linearly correlated with infection rate through stomata, and that no avenalumins were detected in areas adjacent to or apart from the infected area. It was thus considered that avenalumins accumulate locally in infected stomatal sites. In highly resistant interactions, the estimated concentration of avenalumins in an infected stomatal site greatly exceeded the inhibitory level for growth of germ tubes from uredospores. Avenalumins could also diffuse into intercellular spaces of infected leaves. It is postulated that the production of avenalumins is regulated as a result of resistance gene expression and is effective against the development of crown rust fungus in oat leaves.