THE 2ND-PHASE OF COLD HARDENING - FREEZING TOLERANCE AND FRUCTAN ISOMER CHANGES IN WINTER CEREAL CROWNS

Cold-hardening plants at above freezing temperatures significantly con tributes to their overall winter hardiness. However, little research h as been conducted on hardening at temperatures below freezing, before freezing injury results. To determine the effect of hardening at below freezing temperatures, barley (Hardeum vulgare L.) and oat (Avena sat iva L.) were grown and hardened under controlled conditions and freeze tested after being held at -3 degrees C from 1 to 7 d. A significant hardening effect was observed after exposure to below freezing tempera tures. The biggest change, a reduction of 7 degrees C in the temperatu re at which 50% of the population survives, occurred after 7 d at -3 d egrees C in the winter hardy oat cultivar, Wintok. The additional hard ening appeared related to changes in carbohydrate concentration. While wheat (Triticum aestivum L.) and rye (Secale cereale L.) wore not fre eze tested, their changes in carbohydrates were even greater than oat and barley. In oat, the concentrations of all 15 fructan isomers of de gree of polymerization 3 to 5 were lower after the below freezing trea tment while the concentration of fructose and sucrose were higher. Som e carbohydrate concentrations were highly correlated with freezing sur vival under these conditions, but the exact mechanisms behind this rel ationship are not understood. Controlled freeze tests which consistent ly quantitate the effect of individual mechanisms will allow plant bre eders and geneticists to more effectively screen germplasm for winter hardiness genes.