CELLULAR CHANGES IN RELATION TO RUST RESISTANCE

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Abstract
Concomitant studies of the histopathological development and permeability changes associated with the browning reaction of Kubanka wheat to Puccinia graminis Tritici race 34 shows that the browning symptom is caused by encystment of haustoria and brown discoloration of host cell walls. This reaction is accompanied by a progressive permeability increase of host cells to a degree that probably becomes fatal.Extremes of resistance and of susceptibility manifest in the mesothetic reaction are found to be associated, respectively, with local decrease and increase of solute permeability of the host cell membrane.Cold hardening of wheat plants under some conditions caused a more vigorous development of rust and a slight lessening of resistance symptoms, actions that may be associated with a permeability increase induced by hardening. Hardening to cold did not appreciably alter the relative osmotic relationship of fungus and host.Infection of oats, barley, wheat, and corn with appropriate smuts did not change the degree of susceptibility to specific rusts.Evidence is presented that suggests that resistance of Hope wheat in the mature plant stage may be partly determined by lack of availability of water to the parasites. This may also explain regional differences in susceptibility. These are tentative conclusions only.Vital histological examination of the development of resistant flecks on Vernal wheat demonstrates that host cells are killed prior to the occurrence of any discernible injury to fungus organs.A suggestion is made relative to the cause of the different degrees of permeability change associated with different rust reactions.