Effects of Infection by Phytophthora megasperma var. sojae on the Water Relations of Soybean

Soybeans infected by Phytophthora megasperma var. sojae had reduced transpiration rates, lower leaf water potentials, smaller leaves, and higher leaf temperatures than noninfected ones. Flow rates of water through infected soybean roots were one‐tenth those through healthy roots. Recovery from water stress by infected plants was slower than that observed among healthy plants. A 20‐fold greater whole root resistance to water flow was observed in excised roots of infected plants compared to controls. The influence of infection on root resistance greatly exceeded the influence of infection on the size of root systems.