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Seedling Growth of Cicer Milkvetch in Controlled Environments¹

Seedling growth of cicer milkvetch (Astragalus cicer L.) is relatively slow and must be improved before the species can become a valuable forage crop. Therefore, our objectives were (a) to determine the effects of temperature on seedling growth of a seed source with a broad genetic base, and (b) to determine the variability among polycross progenies for seedling growth measurements. Seedlings were grown in controlled environmental chambers at 20 C day and 15 C night temperatures (20-15 C), at 25 C day and 20 C night temperatures (25-20 C), or in the greenhouse.

In the analysis of growth over a 42-day period, seedlings at the two temperature treatments in the growth chambers differed significantly for relative growth rate (RGR), leaf area ratio (LAR), and net assimilation rate (NAR). Seedling growth was most rapid at the 25-20 C treatment. Except for NAR at 25-20 C, growth periods within both temperature treatments differed significantly for RGR, LAR, and NAR. Simple correlation coefficients between shoot weight, root weight, total weight, shoot height, leaf area, and number of leaves were significant and ranged from 0.91 to 0.99 for each treatment. This suggests that any one of the traits studied would be a reliable indicator of seedling vigor.

Significant differences occurred among environments for height, weight, number of leaves, and multileaflet position for seedlings of 22 polycross progenies. Within most environments there also were significant differences among progenies for these traits. The two growth chamber treatments provided better environments for selection of seedling vigor than did the greenhouse. We believe that environmental growth chambers, along with field testing, can be used effectively to improve the seedling vigor of cicer milkvetch.

Key Words: Astragalus cicer L. • Relative growth rate • Leaf area ratio • Net assimilation rate • Polycross progenies • Legume breeding

² Research geneticist and research plant physiologist, SEA, USDA, Crops Research Laboratory, Colorado State Univ., Fort Collins, CO 80523.

Received for publication October 30, 1977.