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Rapid Evaluation of Winter Wheat Residue Decomposition Potential

Posted by Georgine Yorgey | April 10, 2019

In recent months several BIOAg-funded projects came to a close. This post is a summary of one of the finished projects. To read the full project report, please follow the link within the post.

Wheat residue on dry field
Wheat residue on field near Ritzville, Washington, which is part of the a grain-fallow cropping system. (Photo: D. Kilgore)

Managing crop residue is essential to reduced and no-till farming systems that enhance soil health and reduce soil erosion. And growers in different parts of the dryland Pacific Northwest are likely seeking different residue characteristics. In most areas with less than 12 inches of annual precipitation, wheat is grown every other year, and land is fallowed in between to conserve moisture. Having a cultivar which has a slow straw breakdown would help reduce soil erosion by wind and retain more of the scarce water in the soil. In contrast, where annual rainfall exceeds 18 inches, wheat yield, and residue production, is much higher. As a result, when growers try to direct seed into the winter wheat stubble in the spring, it can oftentimes be difficult due to the high amount of remaining residue.

Growers in these areas are searching for cultivars with residue that decomposes quickly. Growers, and the seed dealers they work with, regularly request information on residue decomposition of  winter wheat cultivars, but none is currently available. Arron Carter and colleagues’ 2017 project, “Rapid Evaluation of Winter Wheat Residue Decomposition Potential,” aims to develop efficient methods to provide this information – and lay the groundwork for future breeding efforts that select for wheat varieties with the decomposition characteristics that growers want. The project explored the degradability characteristics of wheat, and how degradability might be dependent on both genetic and environmental factors. It also sought to identify regions of the wheat genome involved in degradability, and to develop new, faster methods for evaluating degradability.

Under the BIOAg project, the team analyzed a set of 151 lines created by crossing two varieties with very different decomposition characteristics (Eltan and Finch). Based on these preliminary results, Carter and his students successfully approached Western SARE to support additional work – as results from the BIOAg project indicated that repeating the work with a population that had more genetic diversity would generate more conclusive insights. They are now repeating the work with a large diversity panel of 480 soft white winter wheat lines from the Pacific Northwest that represents maximized allelic and phenotypic diversity.

The results from these studies indicated that both genetic and environmental factors are important for determining degradability – but not all lines respond to the environment in the same way. Thus recommendations for growers in one location who want a degradable wheat residue are likely to be different than recommendations for growers in another location who want a degradable wheat residue. Using the results the team acquired from the diversity panel, which includes a large number of wheat varieties currently being grown, Carter is now able to give recommendations to growers across the region about varieties they should consider based on their residue needs. He has also discovered that this information is of interest to researchers working on other types of more sustainable systems across the region – for example, those seeking to develop approaches for using wheat straw to produce cellulosic ethanol.

Carter and his team have identified about 20 genomic regions associated with the degradability traits. Each of these genetic regions contributes to a small amount of the variation – indicating that the factors that contribute to degradability are likely to be complex. It also means that selecting for any single one of these genetic regions in breeding is unlikely to have much impact on degradability – though focusing on a set of multiple regions (for example, 6-8 or more regions) could be beneficial. The team is still working with the larger diversity panel to see if they can identify additional genetic regions that are important. In the process, they hope they will continue to develop a better understanding of the genetic factors that contribute to degradability, with the hope of better informing breeding efforts.

Last, the team is working to develop new methods that rely on near-infrared (NIR) spectroscopy for evaluating degradability – methods that would be much faster than the wet chemistry methods currently used. The NIR prediction models generated from their BIOAg data were moderately correlated to trait values, and they are hoping to improve the model once they have finished evaluating the diversity panel.

The BIOAg project supported two graduate students, Alejandra Roa and Nathan Nielsen. Building on the work under BIOAg, USDA-NIFA and the Washington Wheat Commission have awarded funds to make NIR testing standard within the WSU winter wheat breeding program. The OA Vogel and Willard Hennings Endowment, and Western SARE, have supported continuation of this work. The full grant report PDF is available online.

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