Water relations in cotton plants infected with Phymatotrichum omnivorum

Abstract

Water relations in cotton plants infected with Phymatotrichum omnivorum were studied to determine the mechanism of wilt development. Relationships between leaf water and osmotic potentials, relative water contents, and diffusive resistances of leaves from diseased and waterstressed healthy plants were similar, indicating that wilting was not due to changes in leaf osmotic regulation. Rates of recovery from wilting, measured as increases in relative water content with time in both diseased and waterstressed healthy plants were identical. There was no significant difference in root dry weight of healthy and diseased plants, indicating that wilting is not a consequence of reduced root area. Resistance to water flow in roots and lower stems increased significantly over those of healthy plants as upper leaves of diseased plants began to wilt. However, resistance to water flow in petioles of diseased plants was unchanged. These results show that wilting in cotton plants is probably the consequence of increased resistance to water flow in roots. Results of a preliminary study indicate that a high-molecular-weight substance produced by the fungus in culture may cause blockage of xylem elements in roots and lower stems and contribute to the increased resistance to water flow.