A re-evaluation of controlled freeze-tests and controlled environment hardening conditions to estimate the winter survival potential of hardy winter wheats

Abstract

S. 2001. A re-evaluation of controlled freeze-tests and controlled environment hardening conditions to estiomate the winter survival potential of hardy winter wheats. Can. J. Plant Sci. 81: 241-246. To identify superior winter-hardy winter wheat genotypes it is essential to have a reliable screening method that can detect small differences in freezing tolerance. A highly significant correlation was obtained between the minimum temperature tolerated by fully cold-hardened seedlings and the field survival index for 36 winter wheat cultivars with freezing tolerance varying from -13°C to -23°C. On the basis of their long-term field survival under cold stress, these cultivars represent two separate genotypic groups, semi-cold-hardy (Group A) and very cold-hardy (Group B). The correlation coefficient between minimum survival temperature and winter survival for the semi-hardy genotypes was not significant, although it was significant for the hardy genotypes (coefficient of determination was 25.9%). However, the minimum survival freeze test did not differentiate genotypes that varied widely in field survival. In comparing the very hardy winter genotypes (e.g., Norstar, Alabaskaja, Roughrider, etc.), no significant correlation was observed between either minimum survival temperature or crown moisture content. The freezing tolerance of 33 winter wheat genotypes was compared for seedlings naturally cold acclimated and for seedlings grown either in soil or hydroponically and hardened in a controlled environment chamber. On average, soil-grown seedlings, cold acclimated in a controlled environment were more freezing tolerant than seedlings acclimated naturally or grown hydroponically and acclimated in a controlled environment. Several semi-winter-hardy genotypes attained a freezing tolerance equivalent to that of very hardy winter genotypes when acclimated in a controlled environment chamber. Thus, it is possible to overestimate the freezing tolerance of seedlings acclimated in a controlled environment. Les phytogénéticiens ont besoin d'une méthode de présélection fiable pour déceler les petites variations de tolérance au gel qui les aideront à identifier les meilleurs cultivars de blé d'hiver rustique en ce qui concerne la résistance aux conditions hivernales. Les auteurs ont noté une corrélation très significative entre la plus basse température que supportent les plants totalement acclimatés au froid et l'indice de survie au champ chez trente-six cultivars de blé d'hiver dont la tolérance au gel variait de -13°C à -23°C. Selon leur taux de survie au champ à long terme au stress causé par le froid, les cultivars se divisent en deux groupes, ceux à génotype semi-résistant (groupe A) et ceux à génotype très résistant (groupe B). Le coefficient de corrélation entre la température de survie la plus basse et le taux de survie à l'hiver n'était pas significatif pour les cultivars du premier groupe mais bien pour ceux du second (coefficient de détermination de 29,5 %). Le test de survie minimum au gel ne permet toutefois pas de ...

Direct and indirect measurements of freezing tolerance: advantages and limitations

“…This also might be observed in our experiment, where the group of wheat accessions of rather low variation in their winter hardiness (Polish plant breeding programs only) was studied. In the paper by Gusta et al (2001) the correlation coefficient between LT50 for field-cold-acclimated plants and winter survival (FSI) for the group of winter-hardy genotypes was 0.51 (0.15 for semi-hardy accessions), thus it was almost the same as in the case of the accessions studied in our experiment (0.43). In the same study freezing tolerance of plants cold acclimated in the field were better correlated with FSI than the freezing tolerance of the plants cold acclimated in the laboratory (0.73 vs. 0.56).…”

The relationship of LT50 to prolonged freezing survival in winter wheat

“…This result was consistent with the possibility of distinct groups of cultivars with similar ability to survive long-term freezing within the groups, but differences between the groups diminish with longer periods in the frozen state. We suggest that the LT 50 can be used to provide evidence of these groups, but we agree with Gusta et al (2001) that long-term freezing tests are needed to identify genotypes with superior ability to remain viable while frozen for long periods of time.…”

“…The ability of the plants to remain alive in the frozen state for extended periods of time is crucial to surviving the winter months in Canada and the Northern US. Survival in the field is the ultimate measure of winterhardiness of a cultivar, but the use of field survival as a tool in selection is unreliable because of variable winter severity with differential winter kill (Gusta et al 2001), and microgeographic environmental variation resulting in the plants throughout a field being exposed to a wide variation in temperature stress (Fowler 1979).…”

“…The LT 50 of plants grown at low, above-freezing temperatures, first declined, then increased (Mahfoozi et al 2001(Mahfoozi et al , 2000. Nonetheless, it has been shown that survival in the field and the LT 50 , determined at a particular point in the cold acclimation process are often significantly correlated (Gusta et al 1997(Gusta et al , 2001), but not with all cultivars (Gusta et al 2001). Fowler et al (1981) reported that a 18C difference in LT 50 translated to a 30% difference in field survival index.…”

Hv-CBF2A overexpression in barley accelerates COR gene transcript accumulation and acquisition of freezing tolerance during cold acclimation

“…Freezing tolerance was determined using two independent tests previously established to assay freezing tolerance levels of Triticeae cereals (Veisz and Sutka 1989;Gusta et al 2001;Limin and Fowler 2006). One method consisted of isolating the crown region from plants and then subjecting the excised crowns to the target freezing temperatures.…”