Location: Wheat Health, Genetics, and Quality Research
2018 Annual Report
Accomplishments
1. Genetic loci controlling falling numbers identified (Triticum aestivum L.). Preharvest sprouting, the germination of grain before harvest, causes falling numbers below 300 seconds, which result in grain discounts, and soft white wheat is particularly susceptible. ARS researchers in Pullman, Washington, together with collaborators at Washington State University, conducted a genome-wide association study on a large adapted soft white winter wheat population over multiple years and locations under natural and induced conditions that triggered low falling numbers. Genetic loci were identified for resistance to preharvest sprouting and for falling number per se, but these loci were not always the same for both traits, indicating that other factors also contributed to low falling numbers in soft white winter wheat. Regional wheat breeders are using the molecular markers that were identified to select for resistance in their own breeding programs so that producers can reduce their risk of discounts resulting from low falling numbers caused by preharvest sprouting.
2. Ability of winter wheat (Triticum aestivum L) to tolerate freezing. Measured freezing tolerance of winter wheat plants has long been known to be inexplicably, highly variable. ARS researchers in Pullman, Washington, discovered that young winter wheat plants, grown under 12-hour light/12 hour darkness at constant low temperature (4 degrees Centigrade) varied dramatically in their ability to tolerate exposure to subfreezing temperatures, depending on the time of day. Nearly 20 percent greater survival was found if the plants were exposed to subfreezing temperatures in the middle of the dark period, or the middle of the light period, compared to exposure starting at the end of either period, and freezing tolerance cycled from low to high twice in each 24-hour period. Expression analyses of cold-responsive genes and metabolite concentrations showed that most cycled from low to high once per day, leading to the conclusion that at least two distinct signaling pathways, one conditioning freezing tolerance in the light, and one conditioning freezing tolerance in the dark, are active in the wheat plants. The influence of the time of day must be considered for artificial freezing trials to accurately predict freezing survival for winter wheat in the field.
3. Loss of seed dormancy in dry seeds. Preharvest sprouting, the initiation of germination on the mother plant, is one major cause of low falling numbers, which result in poor flour functionality, due to the presence of the enzyme alpha-amylase in the grain. Resistance to preharvest sprouting in wheat (Triticum aestivum L) results largely from seed dormancy, the inability to germinate under favorable conditions. When ARS researchers in Pullman, Washington, used the model plant, Arabidopsis, to compare the transcriptomes of dry after-ripened highly dormant seeds possessing the sly1 mutation with Arabidopsis seeds without the mutation, dormancy loss through after-ripening was associated with increased expression of protein translation genes and decreased expression of histone deacetylase, an enzyme that inhibits gene transcription. The prevention of seed germination in seed dormancy occurs through control of fundamental cellular processes, illustrating that this critical survival trait is essential to seed biology.
4. Near-infrared spectrometry (NIR) as a rapid proxy for the falling number test. Addition of small amounts of low falling number wheat to high falling number wheat results in unacceptable product because the enzyme alpha-amylase is effective at low concentrations. Farmers and elevators must currently wait two weeks for results from the commercial falling numbers test, and, consequently, low falling number wheat is inadvertently mixed with high falling number wheat, resulting in unacceptable financial losses to growers and grain elevators. ARS scientists in Pullman, Washington, and Beltsville, Maryland, collaborated to determine if near-infrared spectrometry (NIR) could be used to rapidly sort high and low falling number grain. While it was possible to find a calibration that worked in one environment, it was not possible to arrive at a calibration that would work for all environments. This is likely because low falling number is caused by two phenomena, preharvest sprouting and late maturity alpha amylase. Published papers claiming that NIR can replace falling number tests are incorrect.
Review Publications
Delwiche, S.R., Steber, C.M. 2018. Falling number of soft wheat wheat by near-infrared spectroscopy: a challenge revisited. Cereal Chemistry. 95(3):469-477.
Martinez, S.A., Thompson, A.L., Wen, N., Murphy, L.R., Sanguinet, K., Steber, C.M., Garland Campbell, K.A. 2018. Registration of the LouAlp (Louise/Alpowa) wheat recombinant inbred line mapping population. Journal of Plant Registrations. https://doi:10.3198/jpr2017.08.0053crmp.
Skinner, D.Z., Bellinger, B.S., Hiscox, W., Helms, G. 2018. Evidence of cyclical light/dark-regulated expression of freezing tolerance in young winter wheat plants. PLoS ONE. 13(6). https://doi.org/10.1371/journal.pone.0198042.
Liu, L., Wang, M., Feng, J., See, D.R., Chao, S., Chen, X. 2018. Combination of all-stage and high-temperature adult-plant resistance QTL confers high level, durable resistance to stripe rust in winter wheat cultivar Madsen. Theoretical and Applied Genetics. https://doi 10.1007/s00122-018-3116-4.
Gizaw, S.A., Godoy, J.V., Garland Campbell, K.A., Carter, A.H. 2018. Using spectral reflectance indices as proxy phenotypes for genome-wide association studies of yield and yield stability in Pacific Northwest winter wheat. Crop Science. https://doi:10.2135/cropsci2017.11.0710.
Lewein, M.J., Murray, T.D., Jernigan, K.L., Garland Campbell, K.A., Carter, A.H. 2018. Genome-wide association mapping for eyespot disease in US Pacific Northwest winter wheat. PLoS One. https://doi.org/10.1371/journal.pone.0194698.
Zhang, C., Si, Y., Lamkey, R., Boydston, R.A., Garland Campbell, K.A., Sankaran, S. 2018. High-throughput phenotyping of seed/seedling evaluation using digital image analysis. Agronomy. https://doi.org/10.3390/agronomy8050063.
Jernigan, K.L., Godoy, J.G., Huang, M., Zhou, Y., Morris, C.F., Garland Campbell, K.A., Zhang, Z., Carter, A.H. 2018. Genetic dissection of end-use quality traits in adapted soft white winter wheat. Frontiers in Plant Science. https://www.frontiersin.org/articles/10.3389/fpls.2018.00271/full.
