RECOVERY AFTER FREEZING IN AVENA-SATIVA L, LOLIUM-PERENNE L AND L MULTIFLORUM-LAM

The pattern of recovery in seedlings of cultivars of Lolium perenne, L. multiflorum and Avena sativa was studied after an artificial freezing test at various stages of hardening. Unhardened plants of the three species were killed at about -6-degrees-C. The temperature at which plant mortality of hardened plants occurred was lower and was characteristic of the genotype, the hardening environment and the duration of the hardening treatment. A detailed analysis of the mode of recovery showed that the actively growing apex of the main tiller did not appear to develop increased resistance to freezing since it was killed at about -6-degrees-C in all hardening treatments. Improved survival of hardened plants at lower freezing temperatures could not be attributed to improved hardiness of the main apex but depended on the ability to establish viable regrowth from lateral tiller buds during the recovery period. This method of recovery is discussed in relation to possible physiological mechanisms of freezing tolerance including the release of apical dominance after death of the main apex and the sufficiency of post-freezing carbon assimilation.