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Seedling Vigor Evaluation of Four Birdsfoot Trefoil Varieties Grown Under Two Temperature Regimes>¹

Seedling vigor of four birdsfoot trefoil varieties was studied in growth chambers, at two temperatures, 21 and 27 C. Vigor was evaluated in terms of relative growth rate and its components, net assimilation rate and leaf area ratio. At 21C, relative growth rate of Leo was superior to other varieties and relative growth rate of ‘Tana’ and ‘Viking’ was superior to ‘Empire’. The superiority of ‘Leo’ over Tana and Viking was attributed to a greater leaf area ratio but the superiority of Leo over Empire was due to a greater net assimilation rate. The greater superiority of Tana and Viking over Empire was due to a greater net assimilation rate.

At 27C, relative growth rate of Leo and Tana was greater than relative growth rate of Empire. The difference was due to a greater leaf area ratio since net assimilation rate of all varieties was the same. Within a temperature, differences in leaf area ratio between varieties were associated with changes in the leaf area to leaf weight ratio since the ratio of leaf weight to plant weight was the same.

With increasing temperature, leaf area ratio decreased as a result of a decrease in the ratio of leaf weight to plant weight. The other component of LAR (the leaf area to leaf weight ratio) increased with increasing temperature, but not enough to counteract the effect of the decrease in the ratio of leaf weight to plant weight. The decrease in leaf area ratio with increasing temperature was not great enough to affect relative growth rate. Both relative growth rate and net assimilation rate at the two temperatures were the same.

Key Words: Seedling Vigor • Birdsfoot Trefoil • Relative Growth Rate • Net Assimilation Rate • Leaf Area Ration

² Agronomist, Crops Research Division, ARS, USDA, and graduate assistant, Plant and Soil Science Dept., Montana State University, Bozeman 59715.

Received for publication June 24, 1968.