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Selection for Drought Avoidance in Sorghum Using Aerial Infrared Photography¹

In previous research, genetic variation in sorghum(Sorghum bicolor L. Moench) drought avoidance (maintenance of relatively high leaf water potential under c(,nditions of soil moisture stress) was revealed. Practical screening for drought avoidance requires a fast field method. The response of near infrared reflectance from plant leaves to leaf water status stimulated the development of such a method, based on infrared photographic imagery of water.stressed sorghum breeding nurseries.

Aerial infrared photography was performed from several altitudes over water-stressed and non-stressed sorghum nurseries at Lubbock, Halfway, and Chillicothe, Texas. Noontime leaf water potentials, as a measure of drought avoidance, were determined in selected strains at each nursery. Total leaf chlorophyll content of the respective strains was determined at Lubbock and Chillicothe. Strain canopy color densities in the resulting infrared color transparencies were analyzed by three methods: l) Scanning densitometry; 2) measurement of integrated light transmittance by manual photometry; 3) visual rating of color density.

Over all locations, the best correlations between canopy color density and leaf water potential across strains were obtained with the photometric method. The poorest correlations were obtained with scanning densitometry. For all methods of color density measurement, the c.3rrelations with leaf water potential across strains were the best at Halfway. At this location, plant canopies were dense, ground cover was almost complete, and film exposure and development were optimal. Leaf chloroFhyll content in the various strains was not correlated with canopy color density, although one strain presented a consistent exception. The method and some guidelines for its utilization are discussed.

Key Words: Sorghum bicolor (L.) Moench • Breeding • Drought resistance • Water stress • Leaf water potential • Remote sensing • Photometry

² Respectively, visiting associate professor, Blacklands Res. Ctr., Temple, Tex., presently at the Volcani Ctr., P.O. Box 6, Bet Dagan, Israel; geneticist, USDA-ARS, College Station, TX 77843; associate professor, Plant Science Dep., Texas A&M Univ., College Station, TX 77843; associate research scientist, Remote Sensing Ctr., Texas A&M Univ., College Station, TX 77843; associate professor, Texas Agric. Exp. Station, Lubbock, TX 79401; and associate professor Texas Agric. Exp. Sm., Vernon, TX 76384.

Received for publication September 21, 1977.