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Title: Differences between wheat genotypes in damage from freezing temperatures during reproductive growth

item Livingston, David
item Tuong, Tan
item ISLEIB, THOMAS - North Carolina State University
item MURPHY, J - North Carolina State University

Submitted to: European Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2015
Publication Date: 1/10/2016
Citation: Livingston, D.P., Tuong, T.D., Isleib, T., Murphy, J.P. 2016. Differences between wheat genotypes in damage from freezing temperatures during reproductive growth. European Journal of Agronomy. 74:164-172.

Interpretive Summary: Many researchers believe unexpected spring freezes have become more frequent as a result of climate change. When wheat is in its reproductive growth stage a sudden spring-freeze can be devastating to yield. Yield reductions from a spring-freeze of up to 90% have been reported in some cases. Very little information is available on cultivar differences in tolerance of wheat to a freeze during spring because cultivars mature at different times; early maturing wheat is less susceptible to freezing than varieties which mature later. We developed a test that permits selecting cultivars all at the same stage making it possible to evaluate them for freezing tolerance while they are all at the same growth stage. We were able to freeze up to 90 wheat cultivars under controlled conditions using this technique. We monitored freezing in a smaller sample of plants using Infra-Red Thermography to confirm which plants froze and found that most plants do not actually freeze even though the soil they are growing in had frozen. In addition we found that most freezing begins at the bottom of the plant and proceeds upward even though the leaves and stems are colder than the soil and have frost on their leaves. All the plants that froze died and were unable to produce a head at all. Only plants which did not freeze (super-cooled), as confirmed by IR thermography, were able to produce a head. Among super-cooled plants three cultivars produced significantly more seeds per plant than 4 cultivars that had the lowest seed count. Results from this study indicate that it is possible to detect significant differences in tolerance or avoidance of freezing during heading of wheat cultivars. This will allow breeders to select superior genotypes in agronomically acceptable populations and potentially mitigate damage caused by unexpected spring freezes.

Technical Abstract: Winter cereal crops in the reproductive stage of growth are considerably more susceptible to freezing temperatures than they are during their vegetative stage during the fall. While damage resulting from spring-freeze events has been documented, information on genotypic differences in tolerance to spring-freezes is scarce. In this research, 10 wheat genotypes were grown in a greenhouse and subjected to a simulated spring-freeze at the mid-boot growth stage under controlled conditions. Spring-freeze tolerance was evaluated as the number of seeds/head 3 months after plants were frozen at -6C for 3 hours. Infra red thermography indicated that plants which had frozen, as evidenced by a prominent heat signature in the region containing the head, were killed and were not able to produce a head. Only plants that had no visible freezing (supercooled) were able to reach maturity and produce seeds. Damage to florets under these conditions may have been similar to that in florets of cold (above freezing) susceptible plants such as rice. While there was no discernible pattern to explain which plants froze and which plants super-cooled, in those that super cooled four genotypes had significantly (p=0.05) higher seed counts after being exposed to freezing than 3 with the lowest seed count. In addition, significant differences between genotypes were found in whole plant survival among those that were confirmed by IR imaging to have frozen. Interestingly, those genotypes with high freezing survival were not necessarily the same as the super-cooled plants with the highest seed count. Spring-freeze tolerance was not correlated with maturity (measured under field conditions) suggesting that genetic improvement in superior cultivars could be made without affecting heading date. In addition, spring-freeze tolerance was not correlated with freezing tolerance of genotypes measured on plants in a vegetative state, either under non-acclimated or cold-acclimated conditions indicating that vegetative freezing tolerance is not a good predictor of spring-freeze tolerance. These results suggest that genotypic differences in the effect of super-cooling in addition to freezing tolerance may be exploited to improve the response of existing cultivars to sudden spring freezes.