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CONSERVATION TILLAGE HANDBOOK SERIES
Selecting Soft White Winter Wheat Varieties For Conservation Tillage
Northwest producers often need to consider some crop management changes in winter wheat production when making the transition from conventional tillage to conservation tillage. Alternative pest management options, such as crop rotation and seeding date, may need to be explored to help control certain disease and weed problems previously minimized by conventional, tillage-intensive systems. Uniform combine residue distribution becomes much more important under conservation tillage. Changes in fertility management may also be needed.
Another common concern producers have when making the transition to conservation tillage winter wheat production is variety selection. Are some winter wheat varieties particularly adapted to conservation tillage conditions? Preliminary research with soft white winter wheat has shown that top yielding varieties under conventional tillage will generally be the top varieties under conservation tillage as well.
Much of the research on developing winter wheat varieties and abroad spectrum of other management considerations for conservation farming has been conducted through the STEEP (Solutions to Environmental and Economic Problems) research program. Since 1975, this comprehensive research program on conservation farming has involved more than 100 USDA-Agricultural Research Service (ARS) and university scientists in Washington, Oregon and Idaho.
More than 10 Northwest researchers have been involved in some aspect of winter wheat varietal development and evaluation for conservation farming in the STEEP effort, Two of the researchers who have concentrated on soft white winter wheat are Robert Allan, USDA-ARS Research Geneticist, and Clarence Peterson, Washington State University Research Agronomist. Both are located at WSU in Pullman. Their research has focused on several different approaches to variety development and selection for conservation farming. Part of their research effort has concentrated on comparative trials of varieties, advanced breeding lines and early genetic selections under no-till and conventional tillage. The goals of that effort were to identify special fitness characteristics for conservation tillage and incorporate the sources of those characteristics into improved genetics background for new varieties.
Comparative Trials Under Two Tillage Systems
Allan and Peterson conducted comparative soft white winter wheat trials under no-till and conventional tillage during 1978 to 1985 at Pullman and/or Colton, WA. Annual precipitation levels at the trial sites were 20.3 and 16.5 inches, respectively. A total of 29 trials were conducted, with 8 following spring peas and21 following either spring barley, spring wheat or winter wheat. The number of entries in the trials ranged from 40 to 130.
A rotary tillage (till) treatment was used to simulate conventional tillage. Both the till and no-till treatment were seeded with a modified deep-furrow hoe drill on 14-inch row spacings. Liquid fertilizer was banded 1.5 inches below the seed row beginning in 1981. Prior to that, the fertilizer was surface broadcast before seeding. Seeding dates were generally between October 15 and November 15.
A number of winter wheat varieties were included in the trials along with the advanced breeding lines and special genetic selections, Some of the regional, common and club varieties of soft white winter wheat included in the trials were Stephens, Daws, Lewjain, Hill 81, Tres, Tyee, Crew and Fare. The researchers found that yield rankings for the varieties were nearly the same under no-till and till treatments. The ratios of no-till yield to till yield for each variety generally ranged from 0.95 to 1.00. A 0.90 yield ratio for Hill 81 was slightly lower than for the other varieties, indicating that it was not achieving its yield potential under the no-till conditions of the trials. However, Peterson has found that Hill 81 has been consistently among the top yielding varieties in no-till trials at Pullman since 1985,
When all 29 trials are considered together, the mean yields of the 2,409 total genotypes from varieties, breeding lines and genetic selections averaged 56 bu/acre for no-till and 58 bu/acre for the till treatments, a no-till to till yield ratio of 0.97.
Implications for Producers
The researchers point out that the results of their comparative studies under conventional tillage and no-till will be helpful for producers in considering which soft white winter wheat varieties to plant under conservation tillage systems. The results of their research indicate that growers should generally select varieties which yield the highest under conventional tillage in their area when evaluating varieties for no-till or other conservation tillage systems.
Allan and Peterson stress, however, that there are other important factors to consider when selecting varieties for conservation tillage, Disease potential, varietal disease resistance and emergence potential can be important considerations, Here are a few examples.
Cephalosporium Stripe Potential
Research has shown that Cephalosporium stripe fungal disease of winter wheat survives on infested wheat residue. The most effective control is 2 years out of winter cereals to allow sufficient time for residue decomposition to reduce the disease inoculum level. Consider the situation of a 2-year crop rotation where the previous winter wheat crop was infested. In this case, producers might consider planting high yielding winter wheat varieties with Cephalosporium stripe tolerance, even if they may not be the highest yielding in that area. This would be particularly important if more of the infested residue remained on the soil surface under a conservation tillage system. If the previous crop of winter wheat was not infested, however, varietal tolerance and tillage system would be less important. Stephens is highly susceptible to Cephalosporium stripe, whereas Lewjain is moderately tolerant to the disease.
In contrast to the 2-year rotation, if the infested winter wheat crop is followed by 2 crop years out of winter cereals in a 3-year crop rotation, the potential for Cephalosporium stripe in the next winter wheat crop would be minimal. This disease suppression benefit of the 3-year rotation would generally occur regardless of tillage system used.
Seeding date also influences Cephalosporium stripe impact, with later seeding reducing infection potential. Therefore, later seeding can partially compensate for lower Cephalosporium stripe tolerance in a variety. However, late seeding lowers overall yield potential and also increases the potential for damage from Pythium root rot. Winter weather conditions, which significantly influence root injury and infestation potential, can often have an overriding effect on disease infestation.
In summary, the significance of Cephalosporium stripe tolerance in the variety can depend on the crop rotation, tillage system following the previous winter wheat crop, whether or not that crop was infested, seeding date, winter weather conditions and other factors,
Another example of a variety selection consideration might be seedling vigor and emergence potential at deeper seeding depths. No-till seeding of winter wheat after chemical fallow is a conservation tillage practice which has gained popularity in recent years. The success of maintaining adequate seed-zone soil water for winter wheat planting has been variable, depending on the location, the residue level and management, and weather conditions during the particular year, In situations where producers are attempting to seed at deeper depths than normal to reach soil moisture, the researchers point out that adapted varieties with strong emergence potential, such as Lewjain, might be considered.
Disease potential, disease resistance and emergence characteristics of the varieties are just some examples of considerations for producers when selecting winter wheat varieties for conservation tillage and conventional tillage systems. These considerations are in addition to yield performance in the area. The researchers point out that some varieties may exhibit special adaptation to conservation tillage conditions for specific locations and conditions. Also, only a small number of the commonly-grown soft white winter wheat varieties were included in the comparative studies. They encourage producers to explore special varietal adaptations in their area and share their findings.
Implications for Future Research
From a research standpoint, the results of the 7-year comparative study under the two tillage systems indicate that a separate soft white winter wheat breeding program is not needed for conservation tillage systems. Allan and Peterson concluded that genetic advances in soft white winter wheat could be made for conservation tillage based on selection for particular characteristics and yield performance under conventional tillage.
A more recent genetics study on winter wheat development for conservation tillage indicates, however, there may still be a potential for a selective breeding program under these conditions. Allan directed a 5-year study completed in 1988 which assessed the use of natural selection to identify winter wheat cultivars and characteristics specifically adapted to no-till systems. He subjected 18 genetic populations to 5 years of natural selection under no-till and conventional tillage treatments. Year-to-year changes in crop characteristics were monitored in the populations.
In one genetically diverse population, yield was significantly increased under no-till by the end of the 5 years. Shifts in specific genes, such as red glumes, club spikes and awned spikes, increased under no-till compared to conventional tillage. Analyses of special biochemical genetic markers also showed that moderate to dramatic divergent changes occurred in the genetic structures of most of the populations between the two tillage systems. The results indicate, for the first time, that a separate breeding program for conservation tillage may be justified.
Soft White Winter Wheat Breeding Emphasis
Other major STEEP breeding efforts by Allan and Peterson on soft white winter wheat have focused on developing crop characteristics which would overcome specific production limitations under conservation farming. These production limitations include diseases associated with earlier seeding dates and weather related stresses. Much of their research is a cooperative effort with other Northwest scientists.
Diseases Associated with Early Seeding
In addition to conservation tillage practices, another approach to controlling soil erosion under winter wheat production is to seed earlier to achieve increased soil protection with larger wheat plants. In the Northwest, one of the greatest obstacles to earlier seeding are diseases associated with early plant growth in the fall. Some of the most important of these diseases are being addressed by Allan and Peterson, and a number of other scientists in the STEEP effort. The diseases include stripe rust, Pseudocercosporella (strawbreaker foot rot, Cephalosporium stripe and barley yellow dwarf virus (BYDV).
Resistance to stripe rust has been effectively exploited by many wheat breeders in the Northwest, Recently, Allan has incorporated a source of resistance to strawbreaker foot rot from a weedy relative of wheat into two new, high yielding soft white winter wheat varieties. These new varieties are Hyak, a club-type, and Madsen, a common-type. Certified seed of these two varieties will be available in the fall of 1989.
Sources of resistance to Cephalosporium stripe are rare and environmental conditions greatly affect the reaction of winter wheat to this disease. However, lines of ''tolerance" to the disease have been identified and successfully incorporated into some new breeding lines in the Northwest. Genetic lines with BYDV tolerance are also being evaluated for possible incorporation into the breeding program.
Weather Related Stresses
Along with resistance to diseases related to earlier seeding or increased surface residue levels, other agronomic characteristics are needed in higher yielding, high quality varieties. These characteristics often include strong emergence and seedling vigor for good stand establishment and cold hardiness.
The first semidwarf varieties of soft white winter wheat were developed in the Northwest in the 1950's. This genetic breakthrough provided a major increase in production potential in the region. There are, however, still some drawbacks to the sernidwarf genetic background, One significant drawback is poor emergence under less-than desirable seedbed conditions, Allan, Peterson and other researchers have a significant research effort concentrated on finding new genes for semi-dwarfism which do not adversely affect emergence and seedling vigor. Some promising genetic lines are being evaluated for incorporation into the breeding program.
Cold hardiness can be an important trait of winter wheat in the Northwest. Significant winterkill during the winter of 1988-89 is a grim reminder of that fact. The variety Daws has generally shown superior cold hardiness compared to other soft white winter wheat varieties, but has other agronomic limitations, such as emergence potential. Significant progress has been made in developing advanced lines with good cold hardiness, as well as improved disease resistance, emergence and yield potential.
us: Hans Kok, (208)885-5971
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