Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Russell Mullen


Drought stress reduced soybean seed yield, but its effect on seed quality was highly variable. Two greenhouse experiments (one in summer and one in winter) and one field experiment were conducted to investigate the effects of drought pre-conditioning on seed yield, size, quality, accumulation of dehydrin-like proteins and soluble sugars in relation to seed quality, and seed mineral nutrients. In summer, soybean (Glycine max L.) plants were exposed at beginning seed fill (R5) to well-watered (WW), sudden stress (SS) (without drought pre-conditioning), and three drought pre-conditioning treatments: one-day stress (ODS), two periods of one-day stress (TDS), and gradual stress (GS) imposed prior to severe drought stress. Three treatments were imposed in winter (WW, SS, and GS). In the field experiment, irrigated and non-irrigated conditions were imposed at R5. Yield and yield components declined in drought-stressed plants regardless of the drought patterns compared with WW plants. In the greenhouse experiments, drought stress increased production of small and medium sized seeds, which also had lower germination. Large seeds from well-watered and gradual-stressed plants had better seed vigor (AA-germination) than seeds from suddenly stressed plants, indicating gradual stress was less harmful to seed vigor than sudden stress. In winter, all drought stress treatments induced dehydrin-like proteins at mid-seed development and reduced the level of soluble sugars in the mature seeds. The reduction in soluble sugars in seeds from drought stressed plants coincided with the reduction in AA-germination. In winter and field experiments, drought stress treatments increased the concentration of P, K, Ca, Mo, Mn, and Cu in seed similar in size and weight to seeds from well-watered plants; but, the concentrations varied between the two experiments. Drought-stress treatments reduced seed size in the winter experiment, but not in field experiment. Medium seeds had lower nutrient content than large seeds. In conclusion, all drought stress treatments reduced yield, yield components, increased production of small and medium seeds, and induced expression of dehydrins at mid-seed development. Well-watered and gradual stress treatment improved seed vigor (AA-germination) of large seeds over that observed in the SS treatment and this reduction in seed vigor was coincided with the reduction in soluble sugars.



Digital Repository @ Iowa State University,

Copyright Owner

Nezar Husein Samarah



Proquest ID


File Format


File Size

212 pages