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This article in AJ

  1. Vol. 88 No. 1, p. 67-72
    Received: Mar 24, 1995

    * Corresponding author(s): usselle@soils.umn.edu


Fluridone Reveals Root Elongation Differences among Alfalfa Germplasms

  1. Lynda L. Meyers,
  2. Michael P. Russelle  and
  3. JoAnn F. S. Lamb
  1. PSRU, USDA-ARS and Dep. of Agron. and Plant Genetics, 411 Borlaug Hall, Univ. of Minnesota, St. Paul, MN 55108-6026



Alfalfa (Medicago sativa L.) is a deep-rooted perennial that may be able to remove nitrate from subsoil beneath the rooting zone of annual crops. Alfalfa cultivars with rapid and deep root elongation would be beneficial for reducing future nitrate contamination of ground water supplies. The objectives of this research were to (i) develop a protocol using the herbicide fluridone {1-methyl-3-phenyl-5-[3-(trifluromethyl) henyl]-4(1H)-pyridinone} as a marker for indicating alfalfa root penetration in soil, and (ii) determine the variability in rate of geotropicroot elongation within and among diverse alfalfa germplasms. Fluridone caused rapid, distinctive bleaching of alfalfa leaves at a rate of 25 mg a.i. kg−1 soil, without being fatal. When transplanted after onset of fluridone symptoms, alfalfa recovered and resumed normal growth and flowering. Alfalfa populations did not differ in sensitivity to fluridone. Decomposition of roots from a fluridone-treated plant did not cause symptom development in other plants. Individual plants within alfalfa germplasms differed by 56 d in onset of symptoms, indicating a similar difference in root activity at 80 cm depth in soil. Mean geotropic root elongation rate for 12 diverse germplasms ranged from 1.12 to 1.40 cm d−1. Populations selected for unique root morphological traits were significantly faster in geotropic root elongation rate than their nonselected parental populations. Our method permits in situ identification of plants with rapid geotropic root elongation rates within heterogeneous populations and has proven useful in germplasm selection.

Joint publication of the USDA-ARS and the Minn. Agric. Exp. Stn. Paper no. 2I 713 of the MAES scientific journal series.

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