The cold resistance of Pacific Coast spring wheats at various stages of growth as determined by artificial refrigeration

Relative winter hardiness of varieties of spring wheat is an important ecological factor in the Columbia Basin of Oregon. Experiments were conducted to determine the value of artificial refrigeration as a means of studying cold resistance in relatively nonhardy varieties, and to find if relative resistance remains constant at different periods of growth. Some of the plants were frozen after being hardened under natural conditions by exposure outside the greenhouse. Others were frozen in an unhardened condition. The varieties were ranked according to winterkilling under field conditions in the Columbia Basin and according to injury in the artificial freezing tests, and the correlation coefficients for these ranks were calculated. The coefficient for winterkilling under field conditions and estimated injury of hardened plants frozen in the seedling stage of development was 0.762 +/- 0.085. The coefficient between field survival and the percentage of plants killed by artificial freezing was 0.740 +/- 0.092. In some instances the differences in cold resistance were shown better by the percentages of plants killed than by leaf injury. Correlation coefficients of 0.636 +/- 0.121 and 0.761 +/- 0.086 were obtained from a comparison of field results with leaf injury and plants killed, respectively, of unhardened plants in the seedling stage. The average injury of unhardened plants was greater than that of hardened plants, especially for the hardy varieties even though frozen at higher temperatures. The association between time of heading and resistance to cold was not sufficiently constant to permit the use of the former as an index of hardiness. The average leaf injury was greater for plants frozen during the day than during the night, but the difference based on percentage of plants killed was not pronounced. The correlation coefficient between field results and plants frozen when in the boot stage of development was 0.818 +/- 0.067. A comparison of injury in the boot stage with data on leaf injury and plants killed in the seedling stage gave correlation coefficients of 0.643 +/- 0.119 and 0.671 +/- 0.112, respectively, indicating a definite relation. The varieties in this experiment, however, differ relatively little in cold resistance when actively growing near the boot stage. Results from freezing varieties in the heading stage were in accord with winterkilling under field conditions and with cold resistance in the seedling and boot stages. Differences between varieties are small, however, and differentiation of varieties at this stage of development appears to be difficult.