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Heat- and Cold-Induced Retention of Inoculum by Leaves. C. E. Yarwood, Professor Emeritus, Department of Plant Pathology, University of California, Berkeley, CA 94720; Phytopathology 67:1259-1261. Accepted for publication 24 March 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1259.

When rust-susceptible corn leaves were heated 5 sec at 55 C before being sprayed with either water or a suspension of uredospores of Puccinia sorghi, the retention of water or spore suspension on both leaf surfaces was increased about 9-fold and infection by Puccinia was increased about 5-fold over that on unheated leaves. If leaves were dipped in water instead of sprayed, the relative increase in retention due to the 55 C treatment was much greater, but the actual deposit was less from dipping than from spraying. With Chenopodium quinoa and C. amaranticolor, the increased retention of water as a result of heat treatment was greater than with corn, but with celery, safflower, cucumber, teasel, sunflower, tomato, tobacco, bean, willow, cowpea, and zinnia there was only a slight increase in retention due to heat, and with buckeye and cotton there was a significant decrease. When corn and Chenopodium leaves were dipped in water at 0 C the retention of water was greater than for water at 5-20 C, but less than that for water at 40-70 C. When corn leaves were heated at 1-10 sec at 55 C and then incubated overnight in a moist chamber, the internal water congestion was greater than for unheated leaves. When tobacco, bean, cowpea, cucumber, and cotton leaves were heated 1-10 sec at 55 C and then immersed in ice water, water congestion of intercellular spaces was slight but was greater than for heat alone, cold alone, or cold followed by heat.