VIEW ARTICLE

Physiology and Biochemistry

Diffusive Resistances of Two Sugarbeet Cultivars in Relation to Their Black Root Disease Reaction. Gene R. Safir, Department of Botany and Plant Pathology, and U.S. Department of Agriculture, Agricultural Research Service, North Central Region, Michigan State University, East Lansing 48824; Charles L. Schneider, Department of Botany and Plant Pathology, and U.S. Department of Agriculture, Agricultural Research Service, North Central Region, Michigan State University, East Lansing 48824. Phytopathology 66:277-280. Accepted for publication 25 August 1975. DOI: 10.1094/Phyto-66-277.

Leaves of sugarbeet (Beta vulgaris) seedlings, 4 weeks old, were inoculated with zoospores of Aphanomyces cochlioides, and diffusive resistances to vapor flow were determined at intervals with a diffusion porometer. Two cultivars were used: the highly susceptible SP63269-0, and the less susceptible SP6822-0. Five days after inoculation, diffusive resistances of leaves of cultivar SP63269-0 averaged 4.5 sec cm^–1, whereas resistance of SP6822-0 averaged 2.6 sec cm^–1. Noninoculated control plants of both cultivars averaged 1.6 sec cm^–1. Inoculated plants of SP63269-0, and those from which water was withheld, had a similar relation between leaf diffusive resistance and leaf water potential. Whole-plant resistances to water transport, calculated from steady-state transpiration data, were 10-fold larger for inoculated plants than for control plants 9 days after inoculation. The increased diffusive resistance of infected plants appears, therefore, to be caused by decreased water supply to leaves.