A Comparison of the Cold Hardiness Potential of Spring Cereals and Vernalized and Non-Vernalized Winter Cereals

Abstract

Both spring and winter cereals cold acclimate in response to low temperatures, however the level of freezing tolerance attained is dramatically different. Winter rye and winter wheat seedlings have the genetic potential to cold acclimate to −30°C and −25°C, respectively. In contrast spring cereal seedlings can only cold acclimate from −7 to −9°C. Genetically winter and spring cereals are similar except winter cereals must be vernalized to initiate the reproductive cycle. A strong association has been established between the degree of vernalization and the degree of freezing tolerance that can be achieved in cereal seedlings. The freezing tolerance, water potential and expression of dehydrin transcripts of seedlings of spring, non-vernalized and vernalized winter cereals was determined using both controlled environment chambers and natural conditions. Winter cereal seedlings rapidly acclimate in response to environmental cues whereas temperatures approaching 0°C are required to induce freezing tolerance in spring cereal seedlings. In contrast to non vernalized seedlings, vernalized seedlings of Puma rye and Norstar winter wheat only acclimate to the same level as spring cereals (−7 to −9°C). The water potential of non vernalized winter cereal seedlings rapidly decreases within 12 hours of exposure to hardening conditions. In contrast, there is little or no decrease in the water potential in spring and vernalized winter cereal seedlings. During the acclimation period, crown moisture content decreased in both vernalized and non vernalized winter seedlings and in spring seedlings, however the largest decrease occurred in the non vernalized seedlings. Northern analysis revealed significant accumulation of dehydrin transcripts in non vernalized seedlings, however there was only a transient increase in transcripts in the spring cereal seedlings. Little or no expression of dehydrin transcripts was detected in vernalized seedlings exposed to hardening conditions. In summary, non vernalized winter cereal seedlings have the ability to decrease their water potential and accumulate dehydrins upon exposure to cold hardening conditions. In contrast, vernalized winter cereal seedlings respond similar to spring cereal seedlings when exposed to low temperature hardening conditions.