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This article in AJ

  1. Vol. 71 No. 4, p. 573-577
    Received: Aug 8, 1978

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Dry Matter and Morphological Responses to Temperatures of Alfalfa Strains with Differing Ploidy Levels1

  1. Nitza Arbi,
  2. Dale Smith and
  3. E. T. Bingham2



Alfalfa (Medicago sativa L.) is grown in a diversity of temperature areas, but there is little information on the response to temperature of strains of different ploidy levels. The objective was to study the response of alfalfa strains of 2x, 4x, and 6x levels of ploidy when grown at three different temperature levels. Plants were grown from seed in pots of soil in three growth chamber regimes; hot (H) 33 C day/24 C night, warm (W) 27/18 C, and cool (C) 21/12 C. All chambers had 18-hour daylengths. Plants were harvested with two schedules; (i) by date (43 days after seeding) and (ii) by maturity (at first flower). First flower stage generally was delayed as temperatures decreased. The 2x was the first strain to flower in the H and W regimes and 4x in the C regime, while the 6x strain was last to flower in all regimes. At the 43-day harvest, shoot height and weight of plant parts for each strain generally were highest in the W regime, followed in order by the H and C regimes. Weights of plant parts at first flower for each strain generally were highest in the C regime, followed in descending order by the W and H regimes, except that 6x yielded least in W. Highest herbage growth rate at first flower was in the C regime for the 2x and in the W or C regime for the 4x, while the rate was similar at all temperatures for the 6x. Total plant growth rates (herbage plus roots) of all three strains at first flower were highest in the C regime followed in descending order by the W and H regimes, except 6x was similar at H and W. Leaf area, leaf weight, and specific leaf weight (SLW) generally increased as temperature decreased. However, leaf area of 2x cut by date and SLW of fix cut at first flower were lowest in W rather than H regime. Thus, the strains reacted differently to temperature. The 2x appeared to grow best in the C regime and the 4x in either the W or C regime. The 6x showed a broad adaptation to temperatures, growing about the same at all temperatures. Development of alfalfas with different ploidy levels than the cultivated tetraploids may be a means of obtaining cultivars with broader temperature adaptation or with better adaptation to low or high growing temperatures.

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