Post-Harvest Dormancy in Wheat
Production Technology - Crops

Gene Krenzer, Richard Austin, and Charles Luper Department of Plant and Soil Sciences
Division of Agricultural Sciences and Natural Resources  
Oklahoma State Univeristy

Post-harvest dormancy refers to the inability of seed to germinate after it has been harvested. Some seeds undergo a biochemical process that must occur before germination is initiated. This may be just a matter of time or other factors may interact with time. Post-harvest dormancy is sometimes nature's way of preventing seed from germinating at the wrong time of year.

In wheat, the germination conditions influence the level of post-harvest dormancy expressed. With higher soil temperature, more post-harvest dormancy is expressed. It is common for laboratories conducting wheat germination analyses within six weeks of harvest to place the moist seed in a refrigerator for two to three days prior to placing them in the germination chamber. This breaks most post-harvest dormancy. The level of post-harvest dormancy is genetically controlled, meaning some varieties could have a high level of post-harvest dormancy while others have very little post-harvest dormancy.

The level of post-harvest dormancy is important to Oklahoma wheat producers who emphasize fall forage production, because they are planting into high-temperature soils which may cause post-harvest dormancy to be expressed. They are also planting earlier than producers planting for grain only. This means there is less time from maturity until planting and the post-harvest dormancy may not have dissipated. Under such conditions, varieties with the genetic potential for high post-harvest dormancy may have low germination, even if adequate soil moisture is present for germination. Once soil temperature decreases (e.g., after a cool rain), the remaining seed are likely to germinate and emerge. Just a few days delay in germination can result in a significant reduction in fall forage production.

For three years, seeds harvested from all varieties planted in the Stillwater variety demonstration strips have been germinated in growth chambers to evaluate post-harvest dormancy. The initial germination is conducted immediately after the July 4th weekend in a chamber set at 95º F day and 75º F night (Fig. 1). At two-week intervals we repeated the germination until all varieties had germinated 90% or more. Using the results of these tests, we assign varieties a post-harvest dormancy rating of low, medium, high, or very high if they germinated above 90% by the first of August, September, October, or later, respectively.

We were able to demonstrate the impact of post-harvest dormancy on fall forage production in the wheat variety trials at Perkins and Chickasha in 2000. At Chickasha the wheat was dusted in on September 19, and rain occurred on September 23. The high temperature on Sept. 23 was 85, but dropped to 56, 63, 73, 80, 83, and 83º F the next six days. We would expect with these temperatures that post-harvest dormancy would not be expressed, and it was not. However, at Perkins we pre-irrigated because of lack of soil moisture. Wheat was planted on October 2 and the high temperature for that day and subsequent days was 94, 95, 91, 76, 57, and 55º F. These above 90-degree days were hot enough to cause the post-harvest dormancy to be expressed.

When the Perkins plots were observed 10 days after planting, all varieties appeared to have an excellent stand except 2174 and Cutter, which appeared to have about 35% stand. By 20 days after planting all plots were up to an excellent stand. At Chickasha, all plots appeared to have a good stand 10 days after germination was initiated by the rainfall.

The following table summarizes fall forage data from these two trials. Varieties are ranked from 1 (highest fall forage yield) to 28 (lowest fall forage). Note that if the post-harvest dormancy rating for a variety was medium or low, then that variety performed relatively well at Perkins compared with Chickasha (e.g., Intrada and Lockett). In contrast, if the post-harvest dormancy rating was very high, then that variety performed relatively poor at Perkins (e.g., Cutter and 2174). The only exceptions were varieties that were either very good (2158) or very poor (Ogallala) forage producers regardless of the location. We conclude that wheat varieties with a very high post-harvest dormancy may not produce maximum fall forage. In addition to 2174 and Cutter, Cimarron, Ok102, and Triumph 64 have high post-harvest dormancy.