Studies in Vernalisation of Cereals

Abstract

Two effects of low temp. during germination are considered mere delay in germination, and the specific vernalizing effect. These were experimentally separated by using anaerobic conditions and high concs. of CO2 as a means of prolonging germination at high temp. Plants of winter rye and wheat, and of spring rye grew to maturity after a maximum exposure of 3 weeks in N at 20[degree]C and 12 weeks at 1[degree]C. Anaerobic conditions resulted in "devernalization" of spring rye with increase in leaf number and delay in anthesis. Spring rye previously devernalized by anaerobic conditions could again be revernalized by low temp., giving it a normal leaf number and a normal time to anthesis. Anaerobic conditions completely prevent vernalization even after 12 weeks at 1[degree]C. The tension of O2 required for complete vernalization is greater than 1/500 normal, though at this level considerable vernalization occurs. The specific effect of low temp. was proved by exposing imbibed grain alternately to air at 1[degree]C and N at 20[degree]C. Equal daily exposures for 12 weeks gave plants indistinguishable from unvernalized; controls with similar alternations of air and N kept at 1[degree]C were completely vernalized. Alternations of 6 days at 1[degree]C in air followed by one day at 20[degree]C in N (total time in air at 1[degree]C 6 weeks) gave completed vernalized plants. Using the same total period of low temp., intermediate values were obtained with different relative durations at the 2 temps., and a linear relation was found between time to anthesis and total duration at 20[degree]C. High temps. bring about quantitative reversal of the low-temp. effect and the specific nature of the action of low temp. is proved.