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Recurrent Selection for 2,4-D Tolerance in Cicer Milkvetch

Crops Research Laboratory, USDA-ARS, 1701 Center Ave., Fort Collins, CO 80526

^* Corresponding author (marciecg{at}lamar.colostate.edu).

Cicer milkvetch (Astragalus cicer L.), a long-lived perennial forage legume, has many attributes that make it well suited for permanent pastures in a sustainable agricultural system. Its relatively poor seedling vigor, however, has reduced its potential. A selective, postemergence herbicide, e.g., 2,4-D [(2,4-dichlorophenoxy)acetic acid], could improve establishment by controlling broadleaf weeds. Therefore, this study was conducted to evaluate the use of phenotypic recurrent selection for increasing the tolerance of cicer milkvetch seedlings to 2,4-D. Seedlings were treated in the greenhouse at the three-leaf stage of development with a 1.0 kg a.i. ha^– rate of 2,4-D. Five cycles of recurrent selection for regrowth at the apical meristem following treatment with 2,4-D increased extended seedling height (total length) 38% more than that of the cultivar Monarch (Cycle 0). Seedlings were visually selected for extended height about 4 wk after herbicide application. Selection for extended height reduced root and total seedling dry weights 21 and 13%, respectively, from the Cycle 0 to the Cycle 1 population. For Cycles 1 through 5, however, extended height was significantly correlated with shoot (r = 0.99), root (0.93) total seedling (0.97) dry weights, and apical meristem regrowth score (0.97), but not with crown meristem regrowth score ( – 0.50). Recurrent selection for increased regrowth at the apical meristem following application of 2,4-D was an effective and inexpensive procedure for increasing the tolerance of citer milkvetch to 2,4-D.

Received for publication January 21, 1994.