ENDOGENOUS CYTOKININ LEVELS AND WHEAT-STEM RUST RESISTANCE

The endogenous cytokinin levels of healthy primary leaves and seeds of a stem rust susceptible wheat cultivar, Little Club, were compared wi th those of Little Club containing the stem rust resistance gene Sr25. Leaf material of the resistant line Little Club Sr25 had a higher lev el of total cytokinin activity than Little Club, whereas seed material of Little Club Sr25 did not always have higher levels of cytokinins t han Little Club. High-performance liquid chromatographic separation of cytokinins from leaf material indicated that the resistant line had h igher levels of cytokinin-like activity, that cochromatographed with z eatin-9-glucoside, trans-zeatin, dihydrozeatin and iso-pentenyladenine , than the susceptible cultivar, whereas the susceptible cultivar had higher levels of iso-pentenyladenine-9-glucoside and iso-pentenyladeno sine-like activity than the resistant cultivar. A number of cultivars would have to be tested before the usefulness of cytokinin levels as a n indicator of resistance could be determined.