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Genetic and Hormonal Control of Shoot and Root Growth of Sorghum¹

Sorghum [Sorghum bicolor (L.) Moench] exhibits a large degree of genetic diversity far shoot development, but diversity in root development has heen virtually unexplored. Tall and short lines of ‘kafir’ and ‘milo’ sorghum that were near-isogenic for height were examined to determine if genes which control height also exert a similar inlluence on root growth. Lines were compared both in hydroponics and in soil-filled (fine sandy loam, Udic Paleustalf) root chambers in the field. Since dwarfing genes in sorghum appear to mediate their response through regulation of endogenous gibberellin (GA) levels, effects of exogenous GA₃ applied to the shoot were also evaluated. In the field, differences in height of approximately 1 m developed between isolines of both kafir and milo, but the taller lines also developed 25 to 39% greater leaf areas. More roots were observed in the upper 60 cm of the soil profile in chambers containing the tall isolines, but when total root numbers were normalized with leaf area there were no differences between isolines. The GA₃ application to tall and 3-dwarf milo plants in hydroponic culture stimulated internode length of both cultivars, but reduced leaf area, root length, and root volume. Shoot dry weights of the tall and short isolines were increased by 19.6 and 9.9%, respectively, by GA₃ treatment, while corresponding root dry weights decreased by 20.7 and 20.4 5%. These results are inconsistent with the hypothesis that gibberellins promote both shoot and root growth in sorghum, and further suggest that the genetic control of shoot growth in sorghum is largely independent from control of root growth.

Key Words: Plant height • Root length • Root volume • Isogenic lines • Milo • Gibberellic acid • Sorghum bicolor (L.) Moench

² Former research assistant, Dep. Plant Sciences, Texas A&M Univ., College Station, Tex.; resident director for research and professor, Texas Agric. Exp. Stn., P. 0. Box 748, Temple, Tex.; professor DeP. of Plant Sciences, Texas A&M Univ., College Station, Tex.; and associate professor, Soil and Crop Sciences, Texas A&M Univ., College Station, Tex. The present address of S. A. Wright is Dairyland Research Int., R. R. Number I , Box 51, Clinton, WI 53525.

Received for publication November 8, 1982.