Date of Award:

5-1973

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant Physiology

Committee Chair(s)

M. Coburn Williams

Committee

M. Coburn Williams

Committee

J. LaMar Anderson

Committee

Martyn M. Caldwell

Committee

Ivan G. Palmblad

Committee

Herman H. Wiebe

Abstract

Wasatch milkvetch [Astragalus miser Dougl., var. oblongifolius (Rydb.) Cronq.] was highest in miserotoxin, a poisonous nitro compound, when potassium nitrate was used as the nitrogen source in nutrient cultures. Ammonium nitrate, added to Hoagland solutions to provide four and one-half times normal nitrogen, lowered percent miserotoxin in the plants. Plants grew abnormally in the greenhouse, producing little growth and becoming periodically senescent. High greenhouse temperatures, up to 45 C, were probably responsible for the abnormal growth.

Attempts to inoculate and fix nitrogen in Wasatch milkvetch with Rhizobium bacteria were unsuccessful in the greenhouse.

In growth chamber studies, percent miserotoxin was higher in Wasatch milkvetch than Columbia milkvetch [Astragalus miser Dougl., var serotinus (Gray) Barneby] and Yellowstone milkvetch [Astragalus miser Dougl., var. hylophilus (Rydb.) Barneby] regardless of temperature combinations. Percent miserotoxin was significantly greater in all varieties at the highest day temperatures (32 C). Differences in percent miserotoxin in the growth chamber may possibly be attributed to genetic differences between varieties.

Field applications of ammonium nitrate, ammonium sulfate and potassium nitrate at 56 and 112 kilograms nitrogen per hectare were applied to the three poisonous varieties of timber milkvetch. No differences in size or vigor were detected in nitrogen treated versus untreated timber milkvetch in the field. Unusually high miserotoxin levels, over 6.0%, were found in Columbia milkvetch collected June 23, 1971. Field applications of nitrogen fertilizers did not significantly affect percent miserotoxin in any timber milkvetch variety. Nitrogen fertilizers significantly raised nitrogen levels in the plants at some locations.

Covering Yellowstone milkvetch to exclude light significantly reduced percent miserotoxin.

Wasatch milkvetch was treated with 2,4-D [(2,4-dichlorophenoxy)-acetic acid] at 0.56, 1.12 and 2.24 kg/ha, atrazine [2-chloro-4-(ethyliamino)-6-(isopropylamino)-s-triazine] at 2.24 and 4.48 kg/ha, and monuron [3-(p-chlorophenyl)-1, 1-dimethylurea] at 0.56, 1.12, 2.24 and 4.48 kg/ha. Columbia milkvetch was treated with 2,4,5-T [(2,4,5-trichlorophenoxy) acetic acid] and silvex [2-(2,4,5-trichlorophenoxy)-propionic acid] at 1.12 and 2.24 kg/ha. Percent miserotoxin in Wasatch milkvetch treated with 2,4-D at 1.12 and 2.24 kg/ha was significantly lower than the controls 10 days following treatment. Silvex and 2,4,5-T likewise lowered miserotoxin concentration in Columbia milkvetch.

Except for 2,4-D, all herbicide treatments significantly increased percent nitrogen in Wasatch milkvetch 10 days following treatment. Plants treated with atrazine at 2.24 and 4.48 kg/ha and monuron at 4.48 kg/ha consistently contained significantly more nitrogen from first to last collection.

Under natural conditions nitrogen is neither limiting for plant growth nor does its availability or concentration in the plant significantly affect miserotoxin metabolism. Enriching the soil with available nitrogen may increase nitrogen levels in the plant but miserotoxin concentration is unaffected.

In the field, the process of photosynthesis, by which the glucose fraction is produced, probably is the limiting factor in miserotoxin production. Miserotoxin level in timber milkvetch is reduced when photosynthesis (a) is blocked by subjecting plants to total darkness; (b) is disrupted by phenoxy herbicides; (c) is reduced by cold temperatures; (d) is terminated by senescence and bleaching.

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