Histological comparison of compatible, mesothetic and incompatible reactions between Puccinia graminis tritici and wheat

Publisher Website
Google Scholar
Abstract
Three races of Puccinia graminis tritici developed by successive mutations to give increased virulence (i.e., incompatible → mesothetic → compatible) on the Sr6 gene for resistance were compared histologically on cv. McMurachy (Sr6 gene) growing at 20.5 °C. The length of the longest hyphae and the size of the lesions remained similar in the three interactions up to 3 days after inoculation and then comparative degrees of growth occurred in the following decreasing order; compatible > mesothetic > incompatible. Necrotic cells in the compatible interaction were infrequent (maximum of 6% of infection sites) and hyphae radiated out from the point of ingress in an unimpeded manner. Although necrosis in the incompatible interaction occurred 1 day in advance of necrosis in the mesothetic reaction, by the 6th day, 98–100% of the infection sites in both systems had necrotic cells. In the mesothetic reaction, hyphae grew beyond the area of necrosis in a high proportion (70% at day 6) of the infection sites whereas the incidence of such growth was much less (8% at day 6) in the incompatible reaction. The role of the hypersensitive reaction in these interactions is discussed.