Relations Among Relative Leaf Water Content, Growth, and Rubber Accumulation in Guayule1

Abstract

The relative leaf water content (RLWC) was determined guayule (Parthenium argentatum A. Gray) to quantify the effect of soil water deficits on growth and rubber yield. The RLWC was measured from June to November of 1982 in guayule cultivars 593, N565‐II, and 11591 that had been planted in April 1981 at Mesa, AR. The RLWC measurements were made 1 h after solar noon on treatments I1 and I6, where the criterion for irrigation was 75 and 90% depletion of the available water in the 0‐ to 180‐cm soil profile, respectively. This resulted in eight irrigations for I1 (1330 mm) and two for I6 (330 mm). The RLWC averaged 80% for It and ranged from 70% to minima of 30 to 40% for I6. Treatment I6 resulted in statistically significant decreases in height (26%), dry weight (51%), rubber yield (39%), and resin yield (55%). These same components increased significantly from the first to the second harvest: height by 16%, dry weight by 57%, rubber yield by 63%, and resin yield by 79%. There were no significant differences among the three cultivars in any of the foregoing items.