Comparison of some Processes in Homogenates and Sections of Healthy Bean Leaves Resistant and Susceptible to the Bacterial Halo-blight Disease

Abstract

In unifoliates of eight lines of bean (Phaseolus vulgaris), four with a pole and four with a bush habit, symptoms of resistance and susceptibility, according to line, developed quickly when plants were inoculated with Pseudomonas phaseolicola on the day when the leaves opened. When older leaves were inoculated symptoms developed more slowly, but the resistant/susceptible difference was retained. Oxygen uptakes by homogenates of healthy unifoliates of the four resistant lines were 30 to 75 per cent. higher than the uptakes by homogenates of those of the four susceptible lines on the day when the leaves opened. Subsequently the uptakes fluctuated somewhat, although those of resistant leaves were always higher. Using leaf sections, rates of respiration and the extents of dark CO₂ fixation were found to be the same in both resistant and susceptible unifoliates at all stages of development. Old healthy resistant leaves decarboxylated indoleacetic acid less rapidly than did old healthy susceptible leaves, but there was no difference in young leaves. The oxygen uptake by homogenates is, therefore, the most promising reaction to pursue in order that the difference between resistant and susceptible leaves might be understood.