Gusta, L. V., O'Connor, B. J. and MacHutcheon, M. G. 1997. The selection of superior winter-hardy genotypes using a prolonged freeze test. Can J. Plant Sci. 77: 15-21. Methods of assessing the freezing tolerance of winter cereals must be improved in order to distinguish small differences due to genotype or environment. Seed of eight winter wheat (Triticum aestivum L. em Thell) cultivars, ranging in winter hardiness, were sown either in mid-August, the first week of September or mid-September. Individual plants of each were collected in late October and stored at either -4°or -8°C. In December controlled freeze tests, employing a cooling rate of 2°C h -1 , could not distinguish the less freezing-tolerant cultivars stored at -4°C. However, by March the less winter-hardy cultivars from the third seeding date stored at -4°C could be distinguished. Seedlings stored at -8°C declined in freezing tolerance more rapidly than seedlings stored at -4°C. In December, the less hardy winter wheat cultivars, Rose, Rita and Siouxland, were less freezing tolerant than the hardy cultivars (e.g. Norstar). Seedlings of Rita and Siouxland from the second and third seeding date died by February when stored at -8°C. Seedings of all winter wheat cultivars were dead by March, except Norstar and Alabaskaja, the most winter-hardy cultivars. Storage of seedlings of wheat, triticale (× Triticosecale Rimpani Wit.) and rye (Secale cereale L.) at either -12°or -15°C readily identified the superior winter-hardy genotypes. For example, in mid-winter both Siouxland and Norstar winter wheat had a similar LT 50 (temperature at which 50% of the plants are killed). However, Siouxland could not tolerate storage at either -12°or -15°C for the same length of time as Norstar. These results support the theory that winter kill in nature is more a function of duration of exposure to sub-lethal temperatures rather than exposure to a minimum low temperature for a short duration as programmed in a conventional freeze test. A more realistic and precise freeze test would be to determine the ability of genotypes to survive lengthy exposure to sub-lethal low temperatures. Nous avons semé des grains de 8 cultivars de blé d'hiver (Triticum aestivum L. em Thell) de divers niveaux de rusticité à la miaoüt, à la première semaine de septembre ou à la mi-septembre. Les plantes entières de chaque cultivar étaient recueillies en fin d'octobre et gardées à la température de -4 ou de -8°C. En décembre, des épreuves de gel contrôlé, utilisant un taux de refroidissement de 2°C ha -1 n'ont pas permis de distinguer les cultivars moins tolérants gardés à -4°C. En mars, cependant, on pouvait distinguer ces mêmes cultivars résultant de la troisième date de semis. La résistance au gel des plantules gardées à -8°C baissait plus rapidement que celle des semis gardés à -4°C. En décembre, les cultivars moins rustiques Rose, Rita et Siouxland étaient moins résistants que les cultivars rustiques, notamment Norstar. Les plants de Rita et de Siouxland provenant des deux dernières dates de se...
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 ...
Gusta, L. V., O'Connor, B. J. and Bhatty, R. S. 1997. Flax (Linum usitatissimum L.) responses to chilling and heat stress on flowering and seed yield. Can. J. Plant Sci. 77: 97-99. The effect of a 5°C chilling treatment at the seedling stage on days to flower, yield and oil quality and quantity was determined for seven cultivars of flax (Linum usitatissimum L.). Three days of chilling delayed flowering in Dufferin, McGregor and NorLin, whereas 5 d of chilling delayed flowering in all cultivars except Andro and Noralta. Seven days of chilling reduced the seed yield of only McGregor, Norlin, NorMan and Vimy. The effect of a 40°C heat stress at the flowering stage on yield and oil composition was determined for the same seven cultivars. A heat stress of 40°C for 3 d reduced the seed yield of NorMan, whereas, a 5 d stress reduced the seed yield of all cultivars except McGregor and Noralta. The composition of the oil was not affected by the heat stress. These results suggest genetic variability exists among flax cultivars for tolerance to chilling and heat stresses. Controlled tests can be used to select superior stress tolerant genotypes. Although flax (Linum usitatissimum L.) is considered to be a cool season crop, air temperature less than 10°C in the spring inhibit both growth and development which can delay flowering (Rowland, G.G., Crop Development Centre, University of Saskatchewan, personal communication). A delay in flowering can result in both reduced oil quantity and quality (lower iodine value) especially if the crop matures under hot and dry conditions (Kenaschuk 1975).It is well established that flax at flowering and seed set is sensitive to heat, particularly to temperatures exceeding 30°C (Dillman and Hopper 1943;Painter et al. 1944;Ford and Zimmerman 1964). Dillman and Hopper (1943) reported high temperatures at the time of flowering reduced both the content of flax oil and iodine numbers. Kraft et al. (1963) found that seed set was reduced at temperatures warmer than 25°C. Partial necrosis of the ovule occurred after 1 d exposure to 31°C and complete necrosis occurred after a 5 d exposure to 31°C. Ford and Zimmerman (1964) reported that a heat period during flowering had a negative effect on boll set. Dybing and Zimmerman (1965) observed increasing temperatures hastened shoot and boll maturity and decreased the numbers of seeds per boll and seed weight. The objectives of this study were to develop methods to screen flax cultivars for both chilling and heat tolerance and to determine if genotypic variation exists within cultivars for resistance to both stresses in regard to flowering, yield, oil content and composition.All studies were conducted over 2 yr using different seed lots from the same location. Each year the experiment was replicated four times in a randomized complete block design. Seven cultivars of flax, Andro, Dufferin, McGregor, NorMan, Noralta, NorLin and Vimy were grown in 13 × 16 cm plastic pots in a mixture of soil: peat: vermiculite (1:1:1). Planting date was the third week of May...
Each year in western Canada, millions of dollars are lost in crop production due to untimely spring and fall frosts. For example, on 11 June 1985 and 6 June 1986, frosts of −7 and −6 °C, occurred in Saskatchewan. From Saskatoon North, on 13 Aug. 1979 a frost of −6 to −8 °C completely devastated all unripe crops. The seeding of frost-sensitive crops such as canola and mustard must be delayed in certain areas to avoid spring frosts. This results in a yield reduction and a delay in maturity which, in turn, can result in crop loss due to fall frosts. If seeding is delayed to avoid killing frosts, early-maturing, lower yielding varieties must be sown. In addition to reducing yield, frosts may induce lesions which provide a means of infection by bacteria and fungi. Fall frosts may result in either a complete loss or reduced quality. Frosted wheat may not be suitable for milling and is often graded as feed. Frost at the soft dough stage can result in poor seed germination which makes seed unacceptable for registration. Fall frosts result in green seeds which are unacceptable to the crushers because green oil is produced. Certain spring crops such as wheat, barley and oats possess a certain degree of frost hardiness. Some of our current cultivars can withstand a frost of −5° to −7 °C with little or no apparent injury. The current cultivars of canola and mustard cannot tolerate −4 °C of frost in the cotyledon stage without being severely injured or killed.Key words: Frost tolerance, wheat, oat, barley, canola, mustard
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