The selection of superior winter-hardy genotypes using a prolonged freeze test

Abstract

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...

Asparagus cultivars with varying adaptation to southern Ontario differ for induction of freezing tolerance in the fall

“…The detection of differences among cultivars for LT 50 values early, but not late, in the fall, suggests the ability to withstand early autumn freezing events may contribute to winter hardiness and survivorship. In winter wheat and alfalfa the most winter-hardy cultivars showed physiological and metabolic changes earlier than those with low hardiness levels (Fowler et al 1981;Gusta et al 1997;Schwab et al 1996;Yoshida et al 1997).…”

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

“…Low-temperature tolerance determined by these tests has been highly correlated with winter survival of winter wheat genotypes that vary greatly in freezing tolerance (Fowler and Gusta 1979). Little or no correlation, however, was observed between field survival and low temperature tolerance using genotypes that had a similar LT 50 (Gusta et al 1997).…”

Phosphorus and nitrogen effects on the freezing tolerance of Norstar winter wheat

“…In both years, available N at a depth of 0-60 cm was only 15 kg of NO 3 -N ha -1 , whereas available P at a depth of 0-30 cm was 10 kg ha -1 in 1985 and 15 kg ha -1 in 1986. Fowler and Brydon (1991) reported that the degree of winter kill in the field was related to the quantity of seed-placed N. Gusta et al (1997) demonstrated that seedlings stored at -8°C dehardened much more quickly than seedlings stored at -4°C. Also, seedlings from a late date of seeding (end of September) dehardened more quickly than seedlings obtained from a sowing date in early September.…”

“…The rate of decrease in freezing tolerance was dependent on cultural practices, environmental effects during acclimation and, most importantly the duration and intensity of subzero temperatures. For example, seedlings stored at -8°C deharden faster than seedlings stored at -4°C (Gusta et al 1997). The objective of this study was to determine if N and P affected the midwinter dehardening of Norstar winter-wheat seedlings stored at -4°C.…”

“…On 26 October 1984, 6 November 1985and 29 October 1986, approximately 200 plants plot -1 were harvested with shovels; the soil was removed by hand, and the plants were stored in a soil peat vermiculite mixture (1:1:1) at -4°C under a 20-cm layer of snow (Gusta et al 1997). Controlled freeze tests were conducted in mid-December, mid-January, early March and early April.…”