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Factors Influencing Vegetative Growth and Flowering in Astragalus cicer L.¹

Cicer milkvetch (Astragalus cicer L.) grows and flowers poorly in the greenhouse during the winter. These characteristics retard progress in a plant improvement program. Therefore, the influence of environmental conditions on vegetative growth and flowering of 36 clones of cicer milkvetch was studied in growth chambers, greenhouse, and field. The four growth-chamber environments were 27 C day-21 C night, 27 C day-16 C and 21 C night (4.5 hours at each temperature), 27 C day.21 C night with a low-temperature pretreatment, and 32 C day-21 C night with a low-temperature pretreatment. The low-temperature pretreatment consisted of placing the clones in the dark for 3 weeks, with 1 week each at 5, 1.5, and _*2 C. Day length in the growth chambers and greenhouses was 15 hours.

There were significant differences among treatments and clones for number of tillers, length of tallest tiller, total dry weight, days to flower, number of racemes, and number of florets. Preconditioning with low temperatures increased number of tillers per plant. Mean plant height was greater in the growth-chamber treatments than in the field or greenhouse, but dry-weight production was highest in the field. The leaf component of total dry weight was higher than the stem component in all environments.

More florets were produced at the 27 C day-21 C night environment with pretreatment at relatively cool temperaturcs than at the other growth chamber treatments. Some clones did not require exposure to low temperature for flower induction. Twenty-one clones flowered in the field the first season, but after going through the winter, all 36 clones flowered the second season. Several dories required exposure to lower temperatures and perhaps for a longer period than those in our low-temperature environment before flowering was induced.

Key Words: Cicer milkvetch • Temperature • Genotype-environment interaction • Cold treatment • Leaf-stem ratio

² Research Geneticist and Range Scientist, respectively, ARS, USDA, Fort Collins, Colo. 80521.

Received for publication September 22, 1972.