Questions remain about wheat vernalization in Nebraska
One of the concerns of Nebraska winter wheat producers during the winter and early spring is stand survival.
With good establishment conditions and proper seeding rates and planting depth, winter wheat is best suited for winter if it went into dormancy at the four-leaf stage.
It is no secret that much of the wheat did not germinate last fall because of dry soil conditions. So it is likely that a significant amount of the current wheat crop germinated during warm days that occurred since January and questions arise over whether this late germinating wheat had time to vernalize.
What is vernalization? The root of the word gives you a clue to its meaning. The Latin word “Vernus” means “of the spring.” Vernalization is a stage in the development of many plants, including believe it or not, bulbs, fruit trees, and nut trees. In agriculture it is most commonly associated with hard red winter wheat.
Vernalization, or exposure of seeds or seedlings to cold temperatures, is an adaptation mechanism of winter-sown cereals. It is basic to breeding and selection of new cultivars. Wheat genotypes vary in vernalization response and genetic control of vernalization is complex.
Most winter wheat varieties require up to 45 days (1,080 hours) accumulated exposure to temperatures of 45 to 32 degrees Fahrenheit at the growing point in order to vernalize. Vernalization begins when the seed begins the germination process, when water is absorbed by the seed. Without adequate vernalization, winter wheat plants will remain vegetative and will not produce grain. Non-vernalized wheat will exert heads much later than normal and heading is erratic, if it occurs at all. Vernalization requirements differ by variety. The exact number of vernalization days for most wheat varieties is not known. There are differences, however, in varieties and generally, early maturing wheat varieties require less vernalization than later maturing varieties.
If a wheat plant has not received adequate chilling to vernalize, then the developing seed head (spikelet) and corresponding stem joints will not be present within the stem. The seed head development and jointing varies by variety and geographic location. Producers whose wheat has emerged recently may be wondering whether their wheat had enough exposure to cold temperatures to vernalize and yield potential. Wheat does not have to emerge as a seedling in order to be vernalized by cold temperatures. As long as the seed has received enough moisture to become physiologically active and begin the germination process, it can undergo vernalization. Winter wheat will vernalize after experiencing three to six weeks of soil temperatures below 48 degrees.
Some varieties require a little longer period of cold to vernalize; and some require less. Jagger, Jagalene and perhaps other varieties containing their parentage have one of the shortest vernalization requirements. In almost all cases, winter wheat planted in the fall will vernalize. The only exception would be if the soil is so dry during the fall and winter months that the seed never becomes physiologically active until later in the spring, and it warms up very quickly in the spring. Most often this is rare, but producers may be experiencing this scenario right now. If the latter is the case, then he may see a reduction in yield of 40 percent to 50 percent, if there is not good moisture and other good growing conditions.
Wheat that emerges late typically has fewer total tillers than wheat that emerges in the fall. Late-emerging wheat is also behind in development, and typically flowers and reaches grain fill later in the spring than fall-emerged wheat. If the spring weather is dry, or if it turns hot and dry early, the yield potential of late-emerged wheat could be even less than 40 percent of normal. However, in a cool spring with adequate moisture, late-emerged wheat will have enough time to develop and fill grain, and can yield relatively well.