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Genotypic Differences in Leaf Osmotic Potential Among Grain Sorghum Cultivars Grown Under Irrigation and Drought¹

Osmotic potential of leaves may have relevance to turgor maintenance and adaptation of plants to water-limited environments. Studies were conducted to determine whether it is possible to detect genotypic differences in leaf osmotic potential in the field and the conditions where screening for this character would be most effective.

Consistent genotypic diffences in osmotic potential of sap expressed from frozen-thawed leaf tissue were found during a 3-year field trial which included 10 sorghum [Sorghum bicolor] (L.) Moench genotypes in the first year. Measurements were taken during periods of minimum and maximum water stress (predawn and midafternoon, respectively) under both frequently irrigated and water-limited conditions. Despite highly significant genotype x environment and genotype x treatment interactions, the ranking of sufficiently contrasting genotypes was similar throughout all conditions with ‘Dwarf Redlan’ maintaining the highest and ‘M35-1’ maintaining the lowest leaf osmotic potential.

Seasonal changes in osmotic and total water potential (pressure chamber technique) indicated progressively increasing levels of predawn turgor potential for both frequently irrigated and water-limited treatments but progressively decreasing levels of midafternoon turgor potential. Maintenance of turgor under water-limited relative to frequently irrigated conditions was exhibited at predawn, but not midday. The low osmotic potentials of M35-1 resulted in higher leaf turgor, compared with Dwarf Redlan, at predawn under frequent irrigation.

It is proposed that differences in leaf osmotic potential may be used to select sorghum genotypes that exhibit contrasting water relations. Selection may be more effective under frequently irrigated conditions and during grain filling than under water-limited environments or during early stages of growth.

Key Words: Sorghum bicolor (L.) Moench • Osmotic potential • Water relations

² Graduate research assistant; former assistant geneticist (present address: Dep. of Agronomy and Range Science, Univ. of California, Davis, CA 95616); and professor, respectively, Dep. of Botany and Plant Sciences, Univ. of California, Riverside, CA 92521.

Received for publication November 2, 1981.

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