Final Report for SW07-025
Project Information
The wheat stem sawfly is the major insect pest for wheat in Montana. We developed a trap crop system using two different mechanisms of resistance. The first is solid-stems, which kills sawfly larvae in the stem. The second is a trait whereby females avoid laying eggs in certain varieties. A solid-stemmed variety is paired with a high-yielding unattractive variety. The sawflies lay their eggs in the solid-stem trap. This allows growers to choose higher yielding varieties for most of their acreage, providing both sawfly control and increased production.
1) Assess the potential of solid-stemmed Choteau spring wheat as a trap crop for control of wheat stem sawfly.
2) Select solid-stem lines from a Reeder/Choteau cross that have high end-use quality and vary in volatile production and stem solidness.
3) Determine the relative ability of the solid-stemmed Choteau/Reeder lines to trap wheat stem sawfly.
4) Provide meaningful outreach to growers regarding sawfly control in general and use of trap varieties specifically.
Climate and marketing make wheat the primary crop grown in the state of Montana. A major impediment to profitable production is the wheat stem sawfly. The project was developed to meet the objectives of Western SARE by integrating the expertise of scientists and growers to develop sustainable methods for control of the wheat stem sawfly. We have developed a novel approach to sawfly control using two plant characteristics. First, wheat with solid stems suppresses sawfly damage and causes high mortality of the insect (Cook et al., 2004). Second, certain wheat varieties produce a high level of volatile compounds that serve to attract egg-laying females (Weaver et al., 2009; Sherman et al., 2010). Our goal was to develop and conduct farm-scale tests of a system whereby wheat stem sawfly females preferentially deposit eggs in attractive, solid-stemmed wheat lines. Solid-stemmed lines were paired with hollow-stemmed, high-yielding lines in replicated field scale traits on two sawfly-infested farms in Montana in each of two years. Our hypothesis was that attractive solid-stemmed lines will serve as a trap crop to protect unattractive, and higher-yielding, hollow-stemmed lines. This project presents a unique approach for sawfly control by combining high levels of plant-produced volatiles to attract the sawfly and solid stems to kill them. The research addressed SARE national goals of enhancing the natural resource base and making efficient use on-farm resources by utilizing natural biological patterns and controls. Western SARE goals included promotion of good land stewardship by providing regional sustainable farming methods without the use of agricultural chemicals.
Our intent was for the outreach plan to be led by an extension specialist. However, both extension collaborators left the university during the course of the project, and thus the outreach program was primarily conducted by PIs Weaver and Talbert through over 30 presentations in all areas of the state. The goal of the outreach program was to involve growers in a fact-based discussion of system-based approach for management of the wheat stem sawfly. A primary educational product was on-site presentations. The short-term outcome of this work was a test of concept for manipulating volatile production and stem solidness in a systems-based approach to sawfly management.
The medium-term impact is increased profitability due to enhanced sawfly control and increased sawfly mortality. The impact can be measured by adoption of the system by growers in sawfly-infested areas. Two producers assisted with all levels of the proposal, from proposal writing to planting and data collection. The Montana Wheat and Barley Committee Board of Directors served as an excellent sounding board for this work during their annual research meeting. In the long term, the best measure of success will be adoption of varieties and the adaptation of production systems by Montana farmers.
A primary approach to sawfly control has been in variety selection, in that solid-stem wheat varieties provide a measure of resistance to damage by the sawfly by impeding development from egg-laying to larval maturity. A critical component of this resistance is a reduction in the stem lodging that is caused by mature larvae. This visual measure of resistance is an important indicator of economically valuable suppression. A recently released wheat variety, Choteau (Lanning et al., 2004), has higher yields than previously released solid-stemmed varieties and very solid stems resulting in high levels of sawfly mortality. However, new hollow-stemmed varieties yield more than Choteau in many parts of the state (http://plantsciences.montana.edu/Crops/Default.htm). As a result, farmers must make systems-based choices in varieties and cultural practices – that is, balancing sawfly resistance with yield potential. Development of a system whereby a solid-stemmed variety could serve as a trap crop for adjacent hollow-stemmed varieties would help farmers achieve both maximum yield potential and sawfly control.
Literature Cited
Cook, J. P., D. M. Wichman, J. M. Martin, P. L. Bruckner, and L. E. Talbert. 2004. Identification of microsatellite markers associated with a stem solidness locus in wheat. Crop Sci., 44:1397-1402.
Lanning, S. K., G. R. Carlson, D. Nash, D. M. Wichman, K. D. Kephart, R. N. Stougaard, G. D. Kushnak, J. L. Eckhoff, W. E. Grey and L. E. Talbert. 2004. Registration of Choteau wheat. Crop Sci. 44:2264-2265.
Sherman, J. D., D. K. Weaver, M. Hofland, M. Butelar, S. P. Lanning, Y. Naruoka, F. Crutcher, N. K. Blake, J. M. Martin, P. Lamb, G. Carlson, and L. E. Talbert. 2010. Identification of novel QTL for sawfly resistance in wheat. Crop Sci. 50:73-86.
Weaver, D. K., M. Buteler, M. L. Hofland, J. B. Runyon, C. Nansen, L. E. Talbert, and G. R. Carlson. 2009. Cultivar preferences of ovipositing wheat stem sawflies as influenced by the amounts of volatile attractants. J. Econ. Entomol. 102:1009-1017.
Cooperators
Research
Two plant characteristics that impact the wheat stem sawfly were exploited for this proposal. First, solid stems impede larval development inside the stem, cause sawfly mortality and reduce lodging of infested plants. Second, spring wheat varieties vary for their degree of attractiveness to the female wheat stem sawfly due to production of specific volatile compounds from the growing plant (Weaver et al., 2009). In side-by-side comparisons, female sawflies lay up to ten times as many eggs in attractive hosts relative to unattractive hosts. Three wheat varieties that vary for solidness and attractiveness are keys to our experiments. Reeder is hollow-stemmed and attractive, Conan is hollow-stemmed and unattractive and the trap Choteau is solid-stemmed and attractive (Table 1).
A fortuitous discovery during the early stages of the study is that the solid-stemmed variety Choteau is itself very attractive to the wheat stem sawfly. Thus, Choteau served as an excellent choice for the trap crop experiments. Experiments were successfully conducted in Conrad MT in 2008 and 2010 and in Havre MT in 2009 and 2010. All experiments were planted by the growers using farm-scale equipment. Establishment of the experiments in Conrad in 2009 and Havre in 2008 were not successful due to weather-related issues and farmer equipment malfunction, respectively. The layout of all trials were a large block of either Reeder (attractive) or Conan (unattractive) flanked on both sides by the attractive solid-stem variety Choteau. The size of the trap/crop plot was determined by the farmer’s seeding equipment. Plots at Conrad were approximately four acres each, involving two seeder passes for the trap Choteau and five seeder passes for the crop to be protected. At Havre, plots were approximately eight acres in 2009 and six acres in 2010. Three replications of each experimental unit (trap plus crop) were established. Our hypothesis was that solid-stem Choteau would attract the female sawfly for egg-laying when next to Conan but would not attract the females away from Reeder. The manifestation of the attraction is the number of larvae in the stems of plants that received eggs.
A second part of the experiment was the development of solid stem lines from a Choteau/Reeder cross that varied in attraction and solid stems for determination of relative levels of sawfly infestation. During the course of the study, we made several genetic discoveries that allowed us to proceed beyond the initial aims of the proposal. In particular, we were able to genetically map the genes that controlled attractiveness of a plant to the female sawfly for oviposition (Sherman et al., 2010). Important genes were identified on chromosomes 2D and 5D, respectively. This allowed us to produce near-isogenic lines in several backgrounds that varied for attraction, similar to the method we described in Blake et al. (2011). These lines were planted in replicated hill plot experiments in Amsterdam MT in 2009 and in Havre and Amsterdam MT in 2010. The Amsterdam 2009 experiment was unsuccessful due to an inadvertent herbicide application by the grower-cooperator. Successful trials were conducted in 2010 at both Havre and Amsterdam. The trials consisted of ten seeds per hill for sets of near isogenic lines that varied for the sawfly-attraction genes. Three replications were planted, and hills were harvested for determination of sawfly infestation per stem harvested. Data allowed us to determine the ability of the genes for attractiveness to aid in sawfly control.
In addition to testing the effects of specific genes, we also tested currently grown varieties for relative levels of attraction to the sawfly. The goal was to identify high-yielding varieties with low attractiveness to the sawfly, so that Choteau would serve as an efficient trap. The impetus for this work is that the unattractive variety Conan does not yield much more than Choteau in many parts of the state, and growers need additional choices. To address this issue, we grew successful replicated studies in Amsterdam in 2009 and 2010 and Havre in 2010 to test current varieties for their ability to be protected by the trap crop (Choteau) from sawfly infestation. Trials consisted of solid-seeded plots of approximately five m2, whereby high-yielding varieties were planted either alone or in blends with Choteau. All experiments contained four replications.
A final objective was to provide meaningful outreach to growers regarding the use of trap crops in sawfly control. Due to the fact that the two extension specialists associated with the project left during the course of the experiments, the PIs for the grant took on the responsibility for this activity. Our goal was to present the trap crop data and theory to growers across the state of Montana in field day settings and at statewide grower-based meetings. In addition, we presented data and discussed direction annually with the Montana Wheat and Barley Committee Board of Directors.
The first objective for this study was the most resource intensive. Our goal was to provide a rigorous test of the concept that a solid stem variety that is attractive to the female sawfly would serve as an effective trap crop when planted beside a relatively unattractive variety. Further, we hypothesized that the attractive solid stemmed variety would not serve as an efficient trap when planted beside an attractive variety. Trap crop experiments were successfully established at four farm sites. Samples were taken for determination of sawfly infestation soon after heading and again at harvest. Analysis of samples taken on green stems in July has been completed for all four trials. The Choteau trap successfully attracted sawfly in all four years when planted next to Reeder. However, Reeder received almost as many eggs as Choteau. Thus, the trap did not keep the sawfly from infesting the crop. The converse result occurred with the Choteau/Conan combination, as very few females flew over Choteau to lay eggs in Conan. Results from the green samples are shown in Appendix Figures 1 and 2.
We have also completed analysis of the 2008 and 2009 harvest samples. In 2008 (Conrad) and 2009 (Havre), samples were taken at harvest for the trap Choteau on both the exterior edge (adjacent to fallow ground) and the interior edge (adjacent to crop). The female sawfly emerge from the fallow ground, thus we expected more sawfly larvae in the exterior of the trap. In addition, samples were obtained from the protected crop. In 2008, the Choteau and the Reeder samples were each 50% infested with sawfly larvae, indicating that the trap did not work. Conversely, the Conan crop was only 10% infested, while the Choteau trap was 50%. Infestation was lower in 2009, but the same trend occurred. There was approximately four times the number of larvae in the trap as in the Conan, while there were statistically similar numbers in both the Choteau trap and the Reeder trap. These results show that Choteau served as an excellent trap when paired with unattractive Conan but not when paired with attractive Reeder. The harvest sample results are shown in Appendix Figures 3 and 4. In 2010, experiments were successfully conducted at both the Conrad and Havre farm sites. We have not finished processing the samples collected at harvest.
In sum, results from the trap crop experiment verified the hypothesis that solid-stemmed Choteau serves as an excellent trap crop for attracting the wheat stem sawfly but only when paired with a relatively unattractive variety such as Conan. Choteau will not function as a trap crop if the variety meant to be protected is highly attractive to the wheat stem sawfly. These experiments provide proof of concept for a novel systems-based approach for wheat stem sawfly control in Montana and surrounding states and provinces.
The second part of our research involved identifying current varieties that would be suitable in trap crop system and to develop new varieties specifically for use in trap cropping. The first part of this work entailed experiments to determine the utility of the key genes controlling relative attractiveness of wheat plants to the female sawfly in field situations. We transferred these key genes into several genetic backgrounds and were able to test their utility in near-isogenic line pairs. Data on number of cut stems per line has been obtained for the 2010 Havre site, and data for infestation based on splitting stems is currently being collected. Analysis of cutting data confirmed the importance of the loci for female attraction Sherman et al. (2010). The effect of the 2D and 5D loci on sawfly cutting were significant at P = .02 and P = .07, respectively. These values will improve as we obtain data on infestation.
The identification and verification of the genetic locations for the sawfly attraction trait has two implications. First, we will be able to breed the trait into a range of varieties tailored for different areas of the state. Second, we will be able to use this information to provide data to farmers regarding which varieties are suitable for use in a trap crop situation. This will allow farmers to choose the best variety for their area based on sawfly control and yield potential.
To further address the goal of identification of suitable high-yielding varieties that are not attractive to the sawfly, we planted the leading Montana varieties in blend experiments with the trap crop Choteau. Our data showed that current popular hard red spring wheat varieties O’Neal and Vida are suitable for the trap crop approach. Both of these varieties are higher-yielding than Conan and will provide additional incentive for growers to adapt the trap crop approach. Conversely, the popular variety McNeal is very attractive to the sawfly, and the trap crop approach will not work with this variety.
Our final objective was to communicate our results and the concept of trap cropping to Montana growers. PIs Weaver and Talbert have each given at least five talks per year to various growers groups, reaching over 1,000 people per year (Appendix Table 2). These included numerous talks at grower field days at locations throughout the wheat growing region of Montana.
The primary impact of this project has been proof of concept that a trap crop approach is an effective method of wheat stem sawfly control, but only if the varieties are chosen correctly. The trap variety needs to be attractive to the sawfly and solid-stemmed to kill the larvae, while the protected variety needs to be less attractive than the trap. Based on our research, and the over thirty presentations we have given in the past three years, many of the more progressive farmers in the state have experimented with some variation of the trap crop system on their own farm. We estimate that at least 35 growers are in this category. However, many of these growers have not selected appropriate varieties, especially for the protected crop. We need to continue the educational aspect for this work. In addition, we were able to screen the most widely grown Montana varieties for their efficacy as protected crops in a trap crop system. Our work provides direction to growers in variety selection and will allow them to choose higher-yielding varieties than Conan for their own farms. In addition, private breeders in the state have begun to evaluate their new varieties for their efficacy in the trap cropping scenario.
The second impact of the project comes from our efforts to understand the basis for the attraction characteristic. In particular, we identified two genetic loci that control the trait (Sherman et al., 2010). This information will be critical for further breeding efforts to improve the economics of using the trap crop system.
Research Outcomes
Education and Outreach
Participation Summary:
Two refereed papers have been published based on results from these studies.
Weaver, D. K., M. Buteler, M. L. Hofland, J. B. Runyon, C. Nansen, L. E. Talbert, and G. R. Carlson. 2009. Cultivar preferences of ovipositing wheat stem sawflies as influenced by the amounts of volatile attractants. J. Econ. Entomol. 102:1009-1017.
Sherman, J. D., D. K. Weaver, M. Hofland, M. Butelar, S. P. Lanning, Y. Naruoka, F. Crutcher, N. K. Blake, J. M. Martin, P. Lamb, G. Carlson, and L. E. Talbert. 2010. Identification of novel QTL for sawfly resistance in wheat. Crop Sci. 50:73-86.
A flier was produced to explain the trap system (Appendix Figure 5).
Approximately 30 talks were given around the state on the subject. Appendix Table 2).
Education and Outreach Outcomes
Areas needing additional study
Our work has clearly shown that the concept of trap cropping, whereby a solid stem variety traps female sawfly from infesting a high-yielding variety, provides a viable control measure. However, our results also show that this approach will only work if the protected variety is less attractive than the trap. We have obtained data on a few other varieties that will be useful to growers. However, new varieties continually enter the market. It is critical that we develop a method to identify those which will function in trap cropping system. This may either be through the use of molecular markers or through actual field experimentation. Challenges exists with both approaches. For instance, a specific marker may not give the same information with all varieties, and we need to determine whether this is in fact the case with the markers we developed during this project. With the field approach, sawfly infestation depends upon weather variables, and field experiments may not have sufficient infestation to give reliable results. In sum, this is an area that we need to conduct further research.
Finally, outreach will continue to be critical. The trap concept works, but growers need to be careful of variety selection. This is more demanding than planting a single mono-culture variety, and growers need to be convinced that the additional production is worth their effort.