Effects of Temperature, Moisture Stress, and Seed Size on Germination of Nine Spring Wheat Cultivars1

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Abstract
To determine if spring wheat (Triticum aestivum L.) cultivars show differential germination responses to varying levels of temperature and moisture stress, various seed‐size lots of nine cultivars were germinated in water at 5, 8, 12, 20, and 30°C, and in polyethylene glycol (PEG 8000) solutions with osmotic potentials of 0.0, ‐0.4, and ‐0.8 MPa at 10 and 20°C. Numbers of germinated seeds were recorded at intervals of 4 to 12 h depending upon temperature and stage of germination. Germination was expressed as a cumulative percentage of the number of seeds germinated by the final recording and, because of the unequal intervals between successive recordings, germination‐time curves were described as logistic functions of time. Each curve was characterized by final germination percentage, median germination time, and maximum rate of germination. Final germination exceeded 90% in all instances. At 20°C, cultivars differed by as much as 7 h in median germination time. Cultivar differences were consistent, though decreasing in magnitude, as temperature increased from 5 to 30°C. Differences in median germination time could not be attributed to differences in rate of water uptake. The reciprocal of median germination time, a measure of rate of germination, was linearly related to temperature. Small seeds germinated faster than large seeds in all cases. Increasing osmotic moisture stress from 0.0 to −0.8 MPa caused median germination time to increase from 90 to 156 h at 10°C and from 36 to 64 h at 20°C. Relative germination times of the cultivars were consistent over the different levels of osmotic moisture stress.