Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Artificial lights may be used to delay flowering of soybean Glycine max (L.) Merrill cultivars. Previous research has suggested that night interruption imposed every other night may delay flowering as much as every-night interruption. The objective of the night interruption study was to evaluate the reproductive development of cultivars when exposed to night interruption every night compared with exposure every other night. One cultivar of each maturity group OO through V was grown in the field at Ames, Iowa, during 1978 and 1979. The four light treatments imposed every night or every other night included illumination from sunset to sunrise, from 2300 to 0030 hours, from 0030 to 0200 hours, or from 0200 to 0330 hours. Control plots were not exposed to artificial light;The average number of days delay in reproductive development beyond the control was twice as great for the every-night treatments as for the every-other-night treatments. Illumination from sunset to sunrise delayed reproductive development significantly more than did night interruption for 1.5 hours. Night interruption near the end of the dark period (0200 to 0330 hours) delayed reproductive development more than the earlier interruptions;Single-seed descent is a widely used breeding method in soybeans to inbreed segregating populations in greenhouses and winter nurseries. The method requires that only a few seeds be produced on a plant each generation; therefore, procedures for rapid seed production are desirable. The objective of the day length study was to determine if the time required to produce a generation of soybeans could be reduced by the use of day lengths shorter than 12 hours. Two strains of each maturity group OO through X, two day-neutral strains, and a reference strain which had been used in previous day length studies were grown in controlled environment chambers under day lengths of 4, 8, and 12 hours. The average number of days to beginning bloom was 34 for the 4-hour, 24 for the 8-hour, and 26 for the 12-hour day lengths. The average numbers of days to maturity was 95 for the 4-hour, 85 for the 8-hour, and 81 for the 12-hour day lengths. The results indicated that no reduction in generation time could be achieved by reducing the day length to less than 12 hours.



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Barry Keith Lawrence



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57 pages