Date of Award:

1975

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Natural Resources

Department name when degree awarded

Range Science

Advisor/Chair:

Eugene J. Cronin

Abstract

Astragalus lentiginosus, which consists of 36 varieties, is one of the principal locoweeds of western North America. The objectives of this study included identification of some of the major factors affecting germination of the seed and survival of the newly established seedlings for several of these varieties.

The seeds of the varieties studied exhibited two mechanisms for dormancy. One is a seed coat that is impermeable to water, and the other is a water-leachable inhibitor. The presence or absence of low-intensity incandescent light (in 14-hour day lengths) had no effect on germination. Of three temperature regimes studied, the regime 7/13 C proved optimal for both total and rapid rate of germination. However, though germinating at lower rates, weeds at -1/4 C and 21/27 C both ultimately reached high percentages of germination. Germination decreased linearly with increasing salinity to almost zero in NaCl solutions of -8.52 bars water potential. Variety araenosus, collected in a salt desert shrub vegetation type showed the highest germination at low temperatures and the greatest salinity tolerance.

Seedling survival work was done with both pre-established and established seedlings at the cotyledon to five leaflet stages of development. Seedlings were considered pre-established from the time of germination until the cotyledons were completely unfolded. Afterwards, the seedlings were considered established.

Germination and survival of pre-established seedlings were inhibited by day temperatures of 21 C under laboratory conditions. Maximum emergence and survival occurred at the low temperature regime of 4/13 C. However, seedlings of the three to five leaflet stages grew best at day temperatures of 30 C; growth was substantially lower at lower temperatures.

Seedlings of var. araenosus displayed the most rapid rate of root growth at 7/12 C while roots of var. vitreus grew at a rate nearly 50 percent lower.

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