Variable increases in cold hardiness induced in winter rape by plant growth regulators

Abstract

Triazole and conventional growth regulators were tested for their ability to extend cold hardiness and improve the winter survival of winter rape (Brassica napus L.). Winter rape plants were grown in the field (Ottawa 45°23′ N) and in growth cabinets. Plant growth regulators (PGRs) were applied during the early vegetative stage and the plants were allowed to cold harden. Cold-hardened plants from the field and cabinet were subjected to freezing and ice encasement tests in the laboratory. Some of the triazole PGRs reduced plant size by limiting cell expansion and increasing cell numbers. While cold hardiness and ice encasement tolerance were increased by some growth regulators, these effects were not consistent with time nor were they reflected in increased winter survival. Natural cold hardening may have eclipsed the PGR-induced hardening.