Non-host Response of Oat Leaves against Rust Infection

Abstract

Non-host responses of primary leaves of oat seedlings (cultivar Shokan 1) following inoculation with uredospores of fourteen rust fungi were investigated. Of the rust fungi used, six were pathogenic on gramineous plants and the remainders were nonpathogenic on any of gramineous plants. The fungi of the former group, except Puccinia zoysiae, differentiated high numbers of appressoria over stomata and produced substomatal vesicles in stomata cavities equally well as the infection with the pathogen, Puccinia coronata avenae. In contrast, all fungi belonging to the latter group failed to grow towards stomata and consequently no essential penetration through stomata occurred. The development of the fungi non-pathogenic on oat within oat leaf tissues was inferior to that of the incompatible race of the pathogen. The difference between both was statistically significant before the haustorium formation could be expected. The previous inoculation of the leaves with the five rust fungi of the former group markedly inhibited the development of the normally compatible race of the pathogen. The incorporation of ³H-uridine and ¹⁴C-leucine into the acid insoluble fraction was greater at 12 or 16hr after inoculation in the leaves invaded by these fungi, as compared with corresponding non-inoculated controls. Administration of either the RNA synthesis or protein synthesis inhibitor, cordycepin or blasticidin S, into the leaves stimulated the development of these fungi. It was therefore postulated (a) that the failure of stomata infection of rust fungi that were non-pathogenic on gramineous plants was attributable to the lack of specific relationships between the fungi and the surface features of oat leaves, and (b) that the restricted development of the fungi that were pathogenic on gramineous plants was due, at least in part, to the activation of defense mechanism induced in the leaf tissues.