Final report for OS22-158
Project Information
The focus of this proposal is to evaluate current peanut commercial cultivars and breeding lines in the pipeline for release for resistance to SCRW feeding. This will increase the sustainability of peanut production by reducing or eliminating reliance on pesticides to control a potentially devastating pest. The entomology department at the Tidewater Agricultural Research and Extension Center (TAREC) will be collaborating with the Peanut Variety and Quality Evaluation (PVQE) program, a multi-state project established in 1968. This program includes Virginia, North Carolina, and South Carolina, and serves peanut producers, breeders, and shellers by screening peanut breeding lines for suitability in the V-C region and South Carolina. The PVQE program is under the direction of PI Balota at the Virginia Tech TAREC (please see "Balota letter of collaboration". Our collaboration will allow us to evaluate six currently planted peanut cultivars (e.g., Bailey, Bailey II, Emery, Sullivan, Walton, and NC 20) in addition to multiple cultivar lines that are in the advanced stage of development (typically 20-30 new lines are evaluated each year) (see Balota et al. 2021a and 2021b for PVQE annual summary ).
We also have the advantage of working on commercial and research farms in multiple states (Virginia, North Carolina, South Carolina) maximizing the opportunity for a range of pest pressure and growing conditions. Importantly, if resistant germplasm cannot be identified, we will generate data on relative maturity rates of these cultivars and lines. Resistant- and or early maturing cultivars can provide farmers a viable strategy for planting high-risk fields and avoiding economic damage from this pest.
The focus of this proposal, identifying resistant cultivars and breeding lines, has a proven record of success (Chalfant and Mitchell 1970, Smith 1970, Smith and Porter 1971). Prior studies have evaluated Virginia type peanut for SCRW resistance in the greenhouse (Chalfant and Mitchell 1970, Smith 1970, Smith and Porter 1971) and field (Coffelt and Herbert, 1994) and identified genotypes with high levels of resistance, although these cultivars (most recently, VA 861101 and AgraTech VC-1) are obsolete. Other lines with reported resistance do not provide complete control in the absence of insecticides (Smith and Porter 1971). The body of current research is lacking in this area, perhaps because of reliance on chemical control. Our proposed research is a critical first step in providing peanut producers a pest control method that does not rely on pesticides.
Our research personnel have a demonstrated record of success working with this pest species, identifying high-risk fields, and evaluating peanut injury and maturity. We annually conduct multiple on-farm experiments for a variety of research projects. Our research programs have the equipment necessary to perform all field and greenhouse experiments (e.g., tractors, planters, trucks and trailers, diggers, growth chambers, penetrometers) and the existing facilities (e.g., research farms, greenhouses, laboratory space) established to perform the proposed work. PIs Taylor and Balota are active leaders of the peanut research and extension communities and organize field days, production meetings, and professional conferences in addition to publishing numerous blogs, Extension publications, magazine articles, and peer-refereed manuscripts. We are confident in our capacity to do quality, repeatable research that can be rapidly communicated to our stakeholders to address an immediate threat to sustainable agriculture in the V-C region. Importantly, our research is supported by both Virginia peanut farmers (please see "Letter of support Paul Rogers, Jr."), Virginia Cooperative Extension Programs (please see "Letter of Support Pittman"), and commodity boards (please see "Letter of support Dell Cotton") and our findings can provide meaningful impact in other peanut producing states.
Objective 1: Quantify SCRW injury and pod maturity in the field
We will evaluate peanut cultivars and advanced breeding lines in replicated randomized complete block design experiments at research stations and cooperating on-farm locations. The PVQE program annually plants research plots on farms and on research stations in Virginia, North Carolina, and South Carolina. We will utilize these experiments, designed to measure yield and quality of new and existing cultivars, to evaluate SCRW injury. Adding SCRW injury observations to existing tests allows us to maximize the benefit of available funding by minimizing costs associated with large, multiyear field projects.
Methods are adapted from Coffelt and Herbert 1994. Briefly, plots will be planted at research stations and cooperating farms. Planting date and early-season thrips injury (on a 1-10 scale) will be recorded because the severity of thrips injury can affect maturity. Pod injury from SCRW will be determined by randomly sampling three plants at each location at two times, end-August and before digging dates. This will allow us to have enough information on maturity to correlate with the injury by SCRW without compromising yield experiments. Pods will be visually examined to determine maturity (mature vs. immature) and injury (injured vs. uninjured). As pods mature, the mesocarp color changes, which allows for maturity ratings and assessing optimal digging date. A process that removes the exocarp to reveal the mesocarp color (commonly known as “pod blasting”) will be used to make maturity assessments (Williams and Drexler, 1981). The profile maturity classes by Williams and Drexler (1981) defines white and yellow pods as immature, and orange, brown and black as mature pods; orange is defined as incipient maturity, brown full maturity, and black over mature pods. Injury from SCRW feeding is distinct from other soil-borne pests and rated by percentage of scarred (outside pod fed upon) and penetrated (pod penetrated and seed injured). Yield will be determined at optimum maturity using the Williams and Drexler (1981) color chart. Data will be entered and analyzed using established statistical procedures. Results from year one of the proposed study will be used to identify promising genotypes for further screening. These genotypes will be planted in year two in fields known to have severe SCRW infestation. The effect of pod maturity on SCRW injury will be analyzed and genotype earliness, in addition to inherent resistance, will be considered for recommendations to use in high-risk SCRW fields.
All other agronomic practices (fertilizer, weed control, leaf spot fungicide program) will be according to standard extension recommendations for peanut production.
Objective 2: Quantify SCRW injury and pod maturity in the greenhouse
A second set of experiments will be performed in the greenhouse to supplement Objective 1 with known levels of SCRW larvae. Methods are adapted from Smith 1970 and Smith and Porter 1971. Briefly, the most promising , based on resistance and or maturity in our field experiments, will be grown in the greenhouse and infested with SCRW larvae reared from laboratory colonies (we have the necessary equipment and knowledge to establish and maintain these colonies). Second instar larvae will be used and allowed to feed and develop naturally. Following three weeks, plants will be removed from pot. Pods will be visually observed for SCRW injury and maturity. Different infestation levels will be tested conditional on the availablility of larvae. Percent maturity and SCRW injury will be compared between cultivars using established statistical procedures. Results will be used to supplement and or enhance results from field experiments.
Potential pitfalls and limitations
We have designed experiments that provide direct answers to key questions regarding varietal resistance to SCRW feeding. Our methods are relatively simple, straightforward, and, most importantly, field-tested and proven in our systems. We acknowledge that any study that depends upon fieldwork risks losses to unforeseen abiotic factors. While we cannot be certain that we will have suitable conditions for fieldwork in all years, we are confident that our most important prerequisite – access to field sites that we can control, with known histories – will be maintained. Our study areas are all within peanut production regions in the V-C region. We have reserved research fields, as well as abundant laboratory space for the work. The analytical methods we use are ones that we have abundant experience with. We performed experiments listed in this proposal in the past and are confident in our ability to perform the work listed here. The most significant challenge is ensuring pest pressure and this is achieved by working on-farm with producers who manage fields with a known history of pest infestations.
We have established protocols to minimize risk associated with the Covid pandemic. Virginia Tech employees and students, existing and incoming, are required to be vaccinated. We have experience presenting to diverse audiences using a variety of digital resources (please see examples in “Outreach Plan”). We have also developed and adhere to good laboratory practices that include use of personal protective equipment, additional cleaning and sanitation procedures, and social distancing.
Cooperators
- - Technical Advisor
Research
Replicated experiments to evaluate southern corn rootworm (SCRW) pod injury and yield for a total of 42 peanut cultivars and advanced breeding lines were established in 2022 and 2023 at four locations: Virginia Tech Tidewater Agricultural Research and Extension Center, Suffolk, VA; a commercial peanut farm in Williamston, NC; North Carolina State University Upper Coastal Plain Research Center, Rocky Mount, NC; and Clemson University Edisto Research and Education Center, Blackville, SC. Each location used a randomized complete block design with two replicates. Plots were 10.6-m long x 2 rows wide. Plots were managed using standard agronomic practices for weed, disease, and thrips management, with standard fertilizer and calcium applications. SCRW injury was assessed after digging by visually examining and categorizing 100 pods as scarred (feeding limited to the outer pod) or penetrated (feeding penetrated the pod hull and into the seed). Peanut maturity was assessed by randomly selecting two plants per plot at digging, removing all pods from the plants, pod blasting the sample with a pressure washer, then arranging the pods by color (white, yellow, orange, brown, black) on a peanut maturity profile board. Orange, brown, and black pods were considered mature while white and yellow pods were considered immature. At the Suffolk and Williamston locations, we investigated whether SCRW injury was affected by dig date (peanut maturity). At these locations we had one dig date at optimal harvest maturity and the other 10 days prior to optimal harvest maturity.
Statistical analyses were performed in IBM-SPSS. We used a generalized linear mixed model to compare SCRW scarred and penetrated pods. Location and treatment (variety or breeding line) and their interaction were fixed factors, and year was a random factor. For digging time analyses, a repeated measures generalized linear mixed model was used with treatment, digging date, and their interaction as fixed factors and year and location as random effects. Nonsignificant interactions were excluded. Fisher's least significant difference (LSD) was used to compare means at α=0.05.
The percentage of scarified pods was not different among varieties and advanced breeding lines (P=0.884) (Fig. 2), but varied across locations (< 0.001). There was no interaction between genotype and location (P = 0.597) and this variable was excluded from the final model.
The percentage of penetrated pods was not different among varieties and advanced breeding lines (P = 0.105) (Fig. 3), but varied across locations (P < 0.020). There was no interaction between genotype and location (P = 0.141) and this variable was excluded from the final model.
The digging time and variety interaction was excluded from the final model due to non-significant effect (P = 0.145). Although overall no significant effect of variety was detected (P = 0.583) (Fig. 4), there was a significant effect of digging time (P < 0.001) (Fig. 5). Early-dug pods had the higher rate of scarified pods.
Although overall no significant effect of variety was detected (P = 0.203) (Fig. 6), there was a significant effect of digging time (P < 0.001) (Fig. 7). Like the scarified pod observations, the early-dug pods had a significantly higher rate of penetrated spots (Fig. 7).
None of the evaluated varieties and advanced breeding lines from this project showed resistance to SCRW feeding. These findings were different from Chali & Mitchell, 1967, where some varieties and/or breeding lines demonstrated resistance to larval feeding . Their screening experiments were in a controlled laboratory setting with a set number of laboratory-reared larvae on sprouted peanut seed, while our experiments focused on SCRW field resistance. Varieties from this earlier study are now obsolete.
Digging timing affected insect injury in our study with later, or optimal, dug plots having less injury. This is contrary to our hypothesis that early digging was expected to show less injury because of shorter exposure time for insects to feed on the crop itself. This is an encouraging finding because producers can continue to dig and harvest at optimal times to maximize yield and quality without increasing insect injury.
Taylor SARE final report Figures
We were unable to maintain a laboratory colony of SCRW for Objective 2. To our knowledge, few such colonies are kept by research or commercial institutions. Being able to use test varieties in a controlled environment would have been confirmation of resistance, or lack thereof, in our varieties and breeding lines. Using a colony and a laboratory-based experiment would mitigate environmental factors. Protocols from prior studies (e.g., Chali & Mitchell, 1967) were not able to be replicated to produce adequate numbers of surviving larvae.
Educational & Outreach Activities
Participation Summary:
Researchers posted the following two YouTube videos on SCRW: https://www.youtube.com/watch?v=po_5p1W5vsI
https://www.youtube.com/watch?v=LaDqWrT_wl0
Researchers presented findings from this project at the Virginia Peanut Production Meeting (Franklin, VA) on February 23, 2023 and on February 22, 2024 (estimated audience of 100 producers at each event)
Hoar, E., S. Taylor, S. Malone, & A. Rashed. Evaluation of current Virginia Peanut cultivars and advanced breeding lines for southern corn rootworm resistance. Presented at the Entomological Society of America National Meeting, National Harbor, MD, November 2023.
Learning Outcomes
Host plant resistance, and making cultural modifications such as planting date, optimal digging date, judicious irrigation practices, and selecting fields based on soil characteristics to reduce losses to southern corn rootworm.
Project Outcomes
While the 42 varieties and advanced breeding lines that we evaluated in this project were not resistant to feeding by southern corn rootworm, there have been resistant ones in the past (they are now obsolete), and there may be some waiting to be discovered. Even though we can not recommend a peanut variety that has resistance to our insect pest of focus, we believe that all of the producers who attended the peanut production meetings gained knowledge about their limited management options for southern corn rootworm via this project.