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Water Stress Status in Guayule as Measured by Relative Leaf Water Content¹

The relative leaf water content (RLWC), defined as the ratio of leaf water content at sampling to that at full turgor, was observed to be a sensitive indicator of soil water deficits for two cultivars of guayule (Parthenium argentatum Gray) in an experiment at Phoenix, Ariz. A year's measurements showed highly significant correlation coefficient values for the linear regression of RLWC on the amount of water in the soil (ram water/170-cm depth of soil). The r values ranged from 0.93 in the dry treatmento 0.78 in the wet treatment of cv. 593, which consistently depleted the soil moisture to lower values than 11591. The RLWC decreased to extremely low values, 30 to 40%, but irrigation restored them to about 75% overnight, accompanied by a gain in leaf area of as much as 30%. The RLWC technique does not require elaborate instrumentation or procedure and may be useful as a guide to irrigation scheduling of guayule.

Key Words: Natural rubber • Plant hydration • Irrigation study • Drought adaptation • Parthenium

² Research plant physiologist and research chemist, respectively, U. S. Water Conservation Laboratory, USDA-ARS, 4331 East Broadway Phoenix, AZ 85040.