FROST-RESISTANCE OF CHINESE SPRING CHEYENNE CHROMOSOME SUBSTITUTION LINES UNDER SHORT-DAY AND LONG-DAY HARDENING CONDITIONS

Investigations were carried out under phytotronic conditions to study the effect of daylength on the frost resistance of a 'Chinese Spring'/ 'Cheyenne' chromosome substitution series. The frost resistance of the 5A, 7A, 4B, 5B, 1D and 5D lines was significantly better when raised and hardened with long-day (16 h) rather than short-day (8 h) illumina tion. The frost resistance-increasing effect of daylength could be dem onstrated after freezing lines 5A and 5D at both -10 degrees C and -12 degrees C. An increase in the duration of illumination in the course of preliminary growth and hardening promoted the development of a high er level of frost resistance. This positive effect was most pronounced for chromosome substitution lines, where the frost resistance was sig nificantly better than that of 'Chinese Spring' even with normal dayle ngths.