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Thesis (M.S.)—University of Nebraska—Lincoln, 1965. Department of Botany (Plant Pathology).


Copyright 1965, the author. Used by permission.


The role of IAA oxidase in resistant and susceptible reactions was examined. Temperature-sensitive isogenic lines derived from the wheat variety Red Egyptian were used as basic host material. They different in a single gene, which imparted resistance to race 56 of stem rust at temperature below 21C, and susceptibility at temperature above 24C. Khapli wheat variety was also assayed in one of the experiments. A daily comparison was made of indole acetic acid (IAA) degradation by healthy and rust-affected first leaf tissue under different temperatures and levels of infection. Leaf sections were incubated with radioactive IAA (as—C14OOH) and the radioactivity released as C14O2 was measured at different time periods during 6 hours.

The resistant combinations developed patterns of decarboxylation during infection which were distinct from those of susceptible reactions. The resistant reactions always led to greater IAA degradation throughout the entire infection cycle as compared to that of uninfected tissues. On the other hand, rates of decarboxylation of diseased susceptible tissue fell below those of the controls with the onset of sporulation. The initial rates of oxidase activity were not significant in determining resistance or susceptibility, the rates being controlled by other factors (level of infection, temperature, light). Factors of probable significance in controlling the IAA oxidase in both resistant and susceptible tissue are discussed.

Advisor: J. M. Daly