PLANTING WHEAT SEED DAMAGED BY FROST BEFORE HARVEST

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Frosts associated with cold fronts during late spring damage winter wheat in Kansas in many years. Damage ranges from light to severe depending on the stage of plant growth, the growing conditions, and the intensity and duration of the frost. Genetic resistance to the problem is not available, and varieties of wheat differ little in susceptibility at similar stages. The symptoms of injury to plants and effects on yield from late frosts are described in Spring Freeze Injury to Kansas Wheat (C646, Kansas Cooperative Extension Service).
The developing kernels of wheat are affected directly by frost during maturation of the crop. However, little information from research is available regarding the effect of injury on the quality of the grain for seed.
Temperatures of 25 to 28°F on May 25-29 caused considerable damage to wheat in northwestern Kansas in 1992. The developmental stage of the kernels ranged from milky ripe to soft dough when the frost occurred, and the reduction in grain yield at harvest varied from slight to severe. Growers were concerned about the suitability of the grain as seed for the next year's crop. They were given general recommendations to test the germination of the seed and to not use grain that was shriveled or had low test weight, because specific advice based on research with frost-damaged seed was unavailable.
The frost in 1992 enabled extensive tests of the suitability of damaged wheat for seed. Samples of hard red winter wheat were obtained from certified seed producers, and their kernel characteristics and performance as seed were determined.
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived. Current information is available from http://www.ksre.ksu.edu.

Procedures
The variety TAM 107 was used because it is the most widely grown in northwestern Kansas. Eleven seedlots were evaluated, and results are presented for four lots that represent a range of injury. A sound seedlot of TAM 107 from the area was the control.
Test weights of the uncleaned seedlots containing 12% moisture were measured by Federal Grain Inspection Service methods. All seedlots, particularly those that were damaged most, contained a large range of kernel sizes. The distribution of sizes was determined by sieving the kernels with 6/64 x 3/4-inch and 5/64 x 3/4-inch slotted screens and calculating the percentages by weight above and below the screens. One thousand kernels in each fraction were weighed to determine their average weight.
Germination of 100 kernels in each of the three size fractions of all seedlots was measured after they were prechilled at 41°F for 5 days and incubated on moistened, heavy paper at 59°F for 7 days. After 15 months of storage at room temperature, germination was measured again without the prechilling treatment. Samples of the seedlots also were subjected to accelerated aging at 104°F for 72 hours, prechilled, and tested for germination.
Ability of the seedlots to form a stand of wheat was estimated by planting the seeds in a greenhouse at different depths. Twenty-five seeds in each size fraction of all seedlots were planted 1, 2, 3, or 4 inches deep in masonry sand, which was moistened as needed, and emerged seedlings were counted twice weekly.
All experiments were in randomized complete block designs with four replications of treatments. Data were analyzed statistically by the general linear model method.

Results
Test weight of the wheat decreased steadily as the level of frost damage increased (Table 1). The nondamaged seedlot had a high percentage of large kernels and few small kernels, whereas the severely damaged seedlot had fewer large kernels and more small kernels. The kernel weights of all size fractions fell as the severity of injury increased.
Germination of large kernels was high after harvest, after storage, and after accelerated aging, regardless of the level of frost injury (Table 2). Medium kernels also germinated well after no or slight injury, but viability dropped after moderate or severe injury. Frost was most damaging to small kernels, which germinated poorly in all tests after moderate or severe injury.
Seedling emergence from different planting depths followed the same pattern as germination (Table 3). Emergence was high from all planting depths for large seeds after all levels of injury. Moderate or severe injury decreased emergence at all planting depths for medium kernels. Emergence was always poorer from small kernels than from large or medium kernels, particularly at the greater levels of frost injury.

Discussion
Frost damage was obviously selective, affecting some kernels and leaving others in sound condition. This selectivity. which probably was associated with differences in maturity among tillers or among kernels on the same spike. has important implications for the use of frost-damaged wheat for seed.
Deficiencies in test weight, germination, and emergence were caused by the increased content of small kernels in frost-damaged seedlots. Moderate or severe This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived. Current information is available from http://www.ksre.ksu.edu.