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L.A. Hunt, Department of Crop Science, Ontario Agricultural College
Cereals often have been characterized as the staff of life to civilization. They provide a neat package of stored energy which can be harvested easily, cleaned and handled, and which can be stored readily, often without special drying.
The true cereals are all members of the grass family, of which the major crops are rice, wheat, maize, barley, oats, rye, sorghum, and various millets. Of these wheat, barley, oats and rye are grown mostly in the temperate regions OF in some tropical regions during their cool season, whilst rice, maize, sorghum and millet are grown in the warmer regions. The temperate species, as contrasted to their more tropical relatives, can be grouped into what are called winter and spring types. The winter types are planted in autumn and gain a head start before the freezing temperatures of winter set in. They mature in early summer. When planted in the spring, winter cereals do not normally head, flower, and produce seed in the same growing season. The over-wintering period is thus necessary for the successful completion of their life cycle. (In scientific jargon they need vernalization). By contrast, the spring types will head quite normally when planted in the spring in the more northerly latitudes, or when grown during winter in the tropical regions. Spring planting of spring varieties that are adapted to a short season (90 days or less) can result in an adequate crop given the long summer daylength of the more northerly regions.
Winter cereals generally yield more than their spring cousins. This is partly a consequence of their becoming established in the soil in the fall so that they are ready to begin growth as soon as the temperatures start to rise in early spring. At that time the soil is generally very wet, making it impossible for the cultivation and seeding of spring types. Associated with the early spring growth is early maturity so that winter types not only escape the damaging effects of drought in late summer, but are usually harvested before disease has built up to severely damaging proportions.
Because of their yield advantage, winter cereals are preferred over the spring type wherever it is possible for them to survive the winter period. The limit to winter cereal production is thus determined by winter hardiness, an aspect that is determined not only by cold tolerance but also by tolerance to certain other conditions associated with winter. The list of factors involved here includes; ice cover; flooding; heaving of the sold by ice formation; diseases that grow under a heavy snow cover; and dry winds. Although these factors must be considered when viewing the local situation, geographic limits to winter cereal production can be delineated fairly well by considering the cold tolerance of the species and the January daily minimum temperature. The following limits were given by a U.S. researcher (Salmon) in the early part of this century:
|Species||Average daily minimum temperature in January (0C)|
* not classified by Salmon
These climatic limits, which were developed some 50 years ago still relate reasonably well to the geographic distribution of the cereal crops. For wheat the distribution in the major areas where winter wheat is grown, is shown in Figures 1, 2, and 3. The maps show that winter wheat accounts for a large proportion of wheat land, and overall some 75% of wheat production is derived from winter types. For the other crops the distributions are not shown, but they can be related to the distribution of wheat by considering differences in cold tolerance.
The approximate climatic limits to distribution are only applicable to current and related varieties. Should plant breeders succeed in producing varieties with greater hardiness, then the limits to production will move northwards, and the winter types will displace spring types. This happened with barley in North America in the 1930's and 40's, at which time winter barley became more firmly established as a crop as far north as Pennsylvania and New York. In Europe at the present time, winter barley is supplanting spring barley in many areas. In France, for example the area of winter barley has increased from some 300,000 ha to more than 1,200,000 ha over the past 12 years, with the total barley area remaining constant. With wheat, a similar situation has been apparent in certain areas. In the Ukraine winter wheat has largely supplanted the spring crop, and this may become more apparent elsewhere as new hardy varieties become widely used. For example a new hardy variety, Norstar, recently has been released for S. Alberta.
In the future it can be expected that winter cereals will continue to replace their spring cousins and become more important on the world scene as new hardy varieties are introduced. The breeding of new hardy varieties of wheat may be accelerated by crossing between wheat and rye. This same process may also result in very hardy varieties of the new crop, triticale. The process of breeding hardier varieties will have to make use of new sophisticated techniques of plant breeding and will be as challenging to researchers as the more startling aspects of genetic engineering. The potential pay-off is large, however as emphasized by Dr. Borlaug, winner of the Nobel Peace Prize for his work in wheat breeding, in an article written jointly with Dr. Krull: "If adequate cold or frost resistance could be found to shift the winter wheat belt northward 300 miles across the prairies and steppes of northern U.S.A. and Canada it could be of enormous benefit. Since winter wheat generally utilize moisture better than spring sown varieties this would be reflected in higher yields and a vast jump in production throughout these regions".
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