Performance Story: Influence of Genotype, Weather and the Growing Environment, and Crop Management on Gluten Strength of CWRS Wheat

Gluten strength is a critical asset of CWRS wheat and is the foundation for the longstanding success of the CWRS wheat brand. Today’s CWRS wheat as a class, has stronger gluten than in the past, but still retains good dough extensibility and mixing tolerance for processing flexibility. Consistency of gluten strength in milling grades of CWRS wheat is the expectation of customers. However, in the past decade, questions have been raised in the industry about excessively variable or even deficient gluten strength of CWRS wheat shipments. This variability results from genetic and environmental factors. Genetic variation of gluten strength is constrained by a robust variety registration system. However, the vast crop-growing region in the Prairie provinces experiences an enormous range of varying weather and biotic pressures which in turn leads to varying gluten strength. The supply chain also factors into this variability because wheat typically flows by rail to lakers or ocean-going vessels from farms in geographically small catchment areas around delivery points with limited or no further comingling. This accentuates regional differences in gluten strength as a result of difference in local growing conditions. There is also the possibility that some management practices, and pesticide applications in particular, may play a role in gluten strength variability.

Objectives of the research:

• Develop a thorough understanding of genotype (G), growing environment (E) and select management practices on gluten strength for breadmaking and the relative magnitude of their influence on gluten strength variability
• Develop or refine and validate methods for efficient evaluation and prediction of gluten strength

Research studies and methods:

The research was organized into three separate subprojects (SP1, SP2 and SP6).  Each subproject involved replicated field trials, optimally fertilized study sites based on soil tests and a selection of prominent CWRS wheat varieties.

• SP1, the main G x E study, encompassed nine varieties and nine growing sites across the Prairie region in 2015, 2016 and 2017 and generated 27 site-years of results.
• SP2 studied the effects of fungicide application at anthesis for Fusarium head blight (FHB) control and preharvest application of glyphosate at physiological maturity. SP2 used six varieties and four sites over three years and generated results for 10 site-years.
• SP6 was implemented in 2017 to study the effects of delayed harvest on gluten strength. SP6 involved four varieties at four Manitoba study sites producing 4 site-years of results.

In all three studies, the same set of wheat properties were evaluated. These included grade and grading factors, milling quality, gluten strength evaluated using a computerized dough mixer (mixograph), flour protein content, and gluten protein quality assessed by fractionating and quantifying the two key gluten proteins, gliadin and polymeric glutenin.

Key results:

• Despite optimally fertilizing field sites to minimize differences in fertility, the range in flour protein contents for samples of individual genotypes across the 27 site-years in SP1 was remarkable (11-17%). This outcome was mainly attributed to differences in growing season weather and highlights the extent of CWRS quality variation.
• Dough mixing properties related to gluten strength of individual genotypes varied considerably across growing sites as a result of growing season weather variation.
• Gluten strength evaluated by dough mixing and proportion of high molecular weight glutenin in flour protein were distinct as a group of quality parameters by having considerably larger genotype variance compared to environment variance and were therefore relatively less sensitive to site-year effects caused by growing season weather variation.
• Among the grading factors that were assessed (test weight, fusarium-damaged kernels (FDK), ergot, midge and sprout damage), FDK stood out as the principal grading factor that influenced grade.
• There was a negative relationship between FDK and gluten strength evaluated by dough mixing and content of high molecular weight (HMW) glutenin, in agreement with published research indicating a cause and effect relationship between degradation of polymeric glutenin protein and increased levels of FHB.
• Genotype differences in gluten strength were more distinct at study sites with higher precipitation and more FHB pressure. This appears to be a novel observation not reported in previous G x E studies.
• Variation in gluten strength was unrelated to variation in protein content. This means that protein content is not a proxy for gluten strength as is often believed. Accordingly, gluten strength would not be expected to be affected by protein segregation. It follows that gluten strength cannot be controlled via the grading system or inferred from the protein content of milling grade samples.
• Dough mixing results based on mean values showed the relatively high gluten strength of varieties Glenn and Carberry, and weakness of variety Harvest, regardless of the growing season or site-year. However, in at least two of the three study years, the leading CWRS variety Brandon (since 2017), as well as Stanley, Stettler and Unity had significantly lower mean gluten strength than Carberry which is the current check variety in wheat registration trials establishing the floor of gluten strength for registration support of a bread wheat line.
• Estimated population distributions of gluten strength by genotype revealed the substantial range of gluten strength that would be expected across the Prairie region for varieties in the study sample set exposed to the same environmental conditions as those in the study. This result indicates that possibly excessive variation of gluten strength in shipments of CWRS wheat persists currently, and is independent of standards for gluten strength evaluation in wheat registration trials which are based on mean values.
• Application of fungicide at anthesis to mitigate effects of FHB had no significant effect on gluten strength or on the underlying protein composition of gluten proteins.
• Preharvest application of glyphosate at label timing and rate had no effect on gluten strength or gluten protein composition.
• Delayed harvest adversely affected wheat grade but had no negative effect on gluten strength. Interestingly, gluten strength was slightly increased for wheat samples from the two most delayed harvest dates.
• An accurate and efficient protein fractionation procedure, developed to distinguish the two main constituents of gluten, provided invaluable data to explain the biochemical nature of gluten strength and its variation. Excellent prediction of gluten strength was achieved based on the proportion of HMW glutenin in flour protein. This result could potentially be exploited to develop a driveway test of gluten strength.

Conclusions:

Results of this study indicate that an issue of deficient and/or excessive variation in gluten strength in CWRS wheat shipments most likely existed in 2013 when this research project was conceived. Furthermore, results of this study go far to explain the reason why issues of variable and/or deficient gluten strength can be noticed by commercial customers of CWRS wheat receiving multiple deliveries of wheat within and between crop years. On the one hand, wheat from different regions of the Prairies impacted by different growing conditions are very likely to have different gluten strengths, especially when varieties in the mix are similar. A complicating factor is when leading wheat varieties in different regions of the Prairies have significantly different levels of gluten strength on average. This was probably the case before the list of designated CWRS wheat varieties was updated by the CGC for the 2019 crop year, and may still be the case today. Additionally, gluten strength of individual varieties can vary widely as the population distribution results show. Variation in gluten strength of wheat shipments is to be expected because comingling wheat from different regions to average regional variations in growing conditions is very limited across the supply chain. As protein content is unrelated to gluten strength and gluten strength is not a grading factor, this issue is likely to persist in the long term. While CWRS wheat class modernization has moved the needle of mean gluten strength to a higher level, and varieties which came through variety registration before Carberry was established as the gluten strength floor gradually fade from production, it is unclear if the uniformity of gluten strength delivered to customers can be substantially improved in the absence of gluten strength as a grading factor, considering all the variation caused by the growing environment.

Recommendations:

For gluten strength to become a grading factor, a driveway test needs to exist. Development of such a test is feasible and justifiable owing to the importance of gluten strength to the CWRS wheat brand. This should be a funding priority in wheat quality research.

Many site-years of data are required to accurately establish the processing quality of wheat varieties. In this regard, the current protocol for quality evaluation of bread wheat lines in wheat registration trials could be viewed as deficient as no results are generated from individual trial locations. Adopting a G x E approach in wheat registration trials, even on a limited basis for a few key quality traits, most notably gluten strength could significantly enhance the reliability of outcomes.

This G x E study has generated considerable new knowledge, but there is a pressing need for more science going forward, as quality and marketing issues related to weather and climate change could seriously challenge the reputation of CWRS wheat as a premium bread wheat class in global markets.