COLD HARDINESS OF SPROUTING WHEAT AS AFFECTED BY DURATION OF HARDENING AND HARDENING TEMPERATURE

Abstract

The cold hardiness of sprouting winter wheat seeds, as measured by exposure to −15 °C. for 16 hours, increased rapidly during the first 5 weeks of hardening and decreased rapidly between the seventh and eleventh week of hardening at 1.5 °C. in the dark. With a slightly higher hardening temperature (3.5 °C.) in the dark, a lower level of cold hardiness resulted; cold hardiness reached a maximum with 4 weeks of hardening and then decreased. Material grown at 5 °C. did not develop sufficient cold hardiness to withstand the freezing temperature. The application of supplementary light during hardening at 3.5 °C. resulted in a slight increase in average hardiness but did not prevent the rapid decrease in hardiness after the fourth week of growth.Sprouting winter wheat will harden to cold in the dark. The ultimate level of cold hardiness attained depends on the hardening temperature, the duration of hardening, and the stage of development of the seedling. Small changes in these factors can result in large differences in cold hardiness.