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Root Initiation and Root and Leaf Elongation of Dependent Little Bluestem Tillers Following Defoliation¹

Newly initiated tillers must survive for a period of time without an established root system and, therefore, are dependent on the parent- shoot for water and nutrients. Little is known about the influence of defoliation on subsequent root initiation and root and leaf elongation in dependent tillers. This investigation, conducted in a controlled environment, was designed to 1) determine the leaf stage at which dependent little bluestem [Schizachyrium scoparium (Michx.) Nash var. frequens R. T. Hubb.] tillers are capable of initiating adventitious roots and 2) compare the influence of two intensities of differential defoliation on root initiation and root and leaf elongation of dependent little bluestem tillers. Treatments included defoliation of the dependent tiller, defoliation of the parent-shoot and defoliation of all plant shoots except for the dependent tiller, to a 3 or 5 cm stubble height.

Adventitious root intiation of dependent little bluestem tillers seldom occurred prior to the fourth leaf stage. Defoliation of only the dependent tiller did not significantly (P 0.05) decrease the number of adventitious roots initiated or suppress mean root length of dependent tillers in comparison with untreated plants. Defoliation of either the parent-shoot or all plant shoots suppressed root initiation and root elongation of dependent tillers to a much greater extent than did dependent tiller defoliation. Mean root and leaf length of dependent tillers differed between treatments where all plant shoots were defoliated, and where only the parent-shoot was defoliated. Mean root length of dependent tillers in the former treatments were 62 and 57% of the corresponding length in the latter treatments for the moderate and severe defoliation intensities, respectively. Mean leaf length of dependent tillers in the former treatments were 135 and 147% of the corresponding length in the latter treatments for the moderate and severe defoliation intensities, respectively.

Following defoliation of all plant shoots, mean leaf length of dependent tillers was greater than in untreated plants while mean root length was less than in untreated plants. When only parent-shoots were defoliated, mean root length of dependent tillers was shorter than in untreated plants, while mean leaf length was unaffected. Reduced rates of dependent tiller root elongation following plant defoliation may reduce forage production by preventing successful establishment of newly initiated tillers.

Key Words: Dependent tiller defoliation • Adventitious root initiation • Differential defoliation • Simulated grazing

² Graduate research assistant and assistant professor, Range Science Dep., Texas A&M Univ., College Station, TX 77843.

Received for publication June 8, 1981.