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This article in AJ

  1. Vol. 70 No. 2, p. 231-237
    Received: Mar 7, 1977

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Quantification of Growth Drought Tolerance and Avoidance of Blue Grama Seedlings1

  1. A. M. Wilson and
  2. J. A. Sarles2



Planting failures with blue grama [Bouteloua gracilis (HBK.) Lag.] prompted the investigation of relationships between physiological and morphological traits and seedling drought resistance. The objectives of this study were to quantify the tolerance and avoidance components of growth drought resistance, determine the conditions under which measurements should be made, and assess the variability among seedlings in characteristics that contribute to drought resistance. Blue grama seedlings were restricted to the seminal primary root, irrigated to maintain favorable soil moisture conditions, and retained in plant growth chambers at either a low or a high relative humidity. When leaf area had increased to the maximum that could be supported by water from the root, tiller water potential was determined for a quantification of growth drought tolerance; and total leaf diffusion resistance, water uptake, and green leaf-blade area were determined for a quantification of growth drought avoidance. Growth drought tolerance, defined as the plant drought that is just sufficient to halt the increase of seedling leaf area, varied among seedlings from about −20 to −40 bars. Growth drought avoidance, defined as the difference between plant drought and the drought of the shoot environment, is related to total leaf diffusion resistance, maximum capacity for water uptake, and seedling leaf area. Estimates of total leaf diffusion resistance varied among seedlings from 6 to 23 sec cm−1 and maximum rates of water uptake varied from 1 to 8 g day−1. Differences among accessions in capacity for water uptake suggest that improvements might be made in a plant breeding program. Additional work is needed to determine whether drought tolerance and total leaf diffusion resistance are heritable traits. The concept of growth drought resistance is particularly useful because it can be quantified for individual seedlings.

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