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2016 Annual Report
Objectives
The long-term objective of this project is to improve integrated pest management (IPM) practices for cereal aphids in wheat, barley, and sorghum in the United States. To achieve this objective enhancing the role of aphid host plant resistance and natural enemies for IPM programs and providing fundamental knowledge of cereal aphid biology and ecology is required. Over the next 5 years we will focus on the following objectives:
Objective 1: Determine the distribution and diversity of resistance-breaking biotypes of cereal aphids in the Great Plains states, identify new sources of resistance for wheat and sorghum, and transfer into suitable genetic backgrounds, to facilitate development of new aphid resistant cereal varieties.
Subobjective 1A: Characterize the biotypic structure of Russian wheat aphid (RWA) populations in wheat and non-cultivated grasses to address biotypic diversity to provide knowledge needed to develop and deploy durable RWA resistance in wheat and barley.
Subobjective 1B: Identify, characterize, and introgress greenbug resistance sources/genes into wheat germplasm.
Objective 2: Determine the distribution and severity of sugarcane aphid in sorghum in the Southwest United States, identify resistant germplasm in sorghum, and evaluate population dynamics to assess the potential for development of resistance-breaking biotypes in this aphid species.
Subobjective 2A: Identify sorghum germplasm with resistance to sugarcane aphid and determine the mechanisms of resistance.
Subobjective 2B: Determine if biotypes exist in sugarcane aphid populations that can overcome sugarcane aphid resistance in sorghum.
Objective 3: Develop and refine methods for field, landscape, and area-wide scale approaches for detecting and monitoring invasive aphid infestations, and optimizing invasive aphid biological control methods in wheat and sorghum.
Subobjective 3A: Develop and refine methods for aphid infestation detection and monitoring in wheat and sorghum based on spatial pattern analysis of multispectral remotely sensed imagery.
Subobjective 3B: Assess resource availability and diversity for the aphid parasite Lysephlebus testaceipes across a range of landscape/agroecosystem diversity levels.
Objective 4: Apply knowledge obtained from aphid genome and transcriptome sequencing to develop plant mediated or other delivery methods for RNAi silencing of critical genes for aphid survival in a broad range of aphids affecting cereals.
Approach
Field and laboratory experiments will be conducted to : (1) characterize the biotypic structure of Russian wheat aphid (RWA) populations in wheat and non-cultivated grasses to address biotypic diversity to provide knowledge needed to develop and deploy durable RWA resistance in wheat and barley; (2) identify, characterize, and introgress greenbug resistance sources/genes into wheat germplasm; (3) identify sorghum germplasm with resistance to sugarcane aphid and determine the mechanisms of resistance; (4) determine if biotypes exist in sugarcane aphid populations that can overcome sugarcane aphid resistance in sorghum; (5) develop and refine methods for aphid infestation detection and monitoring in wheat and sorghum based on spatial pattern analysis of multispectral remotely sensed imagery; (6) assess resource availability and diversity for the aphid parasite Lysephlebus testaceipes across a range of landscape/agroecosystem diversity levels; and (7) apply knowledge obtained from aphid genome and transcriptome sequencing to develop plant mediated or other delivery methods for RNAi silencing of critical genes for aphid survival in a broad range of aphids affecting cereals.
Progress Report
Under Subobjective 1A, a survey of biotypic structure of RWA biotypes conducted from 2010 to 2013 found a significant shift in biotype structure from that reported in 2007. There is a great need to continue monitoring biotype structure in RWA to insure resistance sources that are currently being developed for resistance to RWA2 will be effective in the future. The costs of these surveys preclude a yearly survey on biotype structure at a regional level, thus, these surveys will be conducted every 4-5 years since the previous survey. For this reason, there was no 12 mo. milestone for this objective since this study will not be initiated until 2017. This gap provided an opportunity to conduct a survey on a new pest of cereal that was discovered in oats in New Mexico in late 2014. This pest has been demonstrated to cause significant damage to wheat. Our survey has determined that this pest is distributed throughout New Mexico and Colorado. More importantly, in spring of 2016 we discovered it has expanded its range into the primary winter wheat belt in the Great Plains region of Colorado.
Under Subobjective 4A, the genome assembly produced by this project, Dnox_1.0 and its RefSeq (available of GenBank) used gene and protein sequences to identify 25 new gene targets and have made the constructs for an RNAi approach. A feeding bioassay is in progress to determine the optimal sucrose concentrations in the artificial diets for four aphid target species, Russian wheat aphid, greenbug, soybean aphid, and green peach aphid. These target aphids are among the most destructive to agricultural crops and the objective is to identify RNAi constructs and target genes that are most effective against these species. The feeding bioassay to optimize the diet will be completed this FY.
Under Objective 3A, the first year, imagery was acquired to initiate a database of remotely sensed data for differentiating sorghum fields infested by sugarcane aphid from non-infested fields. Preliminary evaluation indicates that sugarcane aphid infestations in sorghum fields are very aggregated and distinctive visually, which should permit development of a statistical model (or models) that can be used to distinguish sugarcane aphid infested sorghum fields stressed by other factors. Under Objective 3B, the first year of field data on parasitism of aphids in wheat fields in landscapes dominated by wheat and in wheat/canola dominated landscapes was obtained. Preliminary evaluation indicates that while canola provides resources for parasitoids in wheat, and there is spillover of parasitoids from canola into wheat, parasitism of aphids in wheat may not be increased by the presence of canola in the landscape. However, additional year's data will be required before a definitive statement is possible.
Under Objective 1, we have screened a set of 2,500 wheat germplasm, and reselected one line resistant to greenbug biotype E from PI 595379. We further made a cross (PI 595379-1/PI243735) to derive a mapping population. An F2 population consisting of 270 plants is currently grown in a vernalization chamber, and we expect to get F3 seeds at the end of 2016. The F3 lines will be evaluated to map the greenbug resistance gene in PI 595379-1 in early 2017. Collaborating a research group at Texas A&M University, we have evaluated a recombinant inbred line population derived from a cross "W7984 x Opata_M85" to fine map the greenbug resistance gene Gb4. SNP markers closely linked to the Gb4 gene have been converted to KASP markers for marker-assisted selection. Collaborating with Oklahoma Wheat breeding Team, we have selected a set of F7 lines resistant to both greenbug biotype E and Russian wheat aphid biotype 2 from two breeding populations. These lines will be further evaluated and selected in the field.
Under Objective 2, several collaborative research relationships have been made between the USDA-ARS research entomologists at Stillwater and sorghum plant breeders from Texas A&M, other USDA-ARS laboratories, and industry sorghum breeders. This work has led to the identification of host-plant resistance in both grain and forage sorghums. The WPOFC USDA-ARS laboratory also identified cross-resistance for greenbug resistance which is commercially available in grower adapted lines and this was conducted through Industry MTRA's. Two new parental lines were released to the public in 2016 from collaborative work with the Texas A&M as well as hybrids have been identified. The genetics for grain sorghum resistance is also in 2 parental forage sorghums, and will be released within months. Two sources of resistance from the introgressive breeding at the USDA-ARS Laboratory in Lubbock, Texas, have recently been identified with plans for a release within 2016. Genetic analysis of sugarcane aphids was conducted, and a manuscript written that shows very little diversity or divergence in individuals collected the sorghum growing regions of the south, central, and south central U.S. Collaborative research on the genetic background of the sugarcane aphid with regards to host specificity (biotypes) has been conducted and shows that the sugarcane aphid has a low genetic diversity from the collections within the United States and some South African nations. More plant phenotypic response research needs to be conducted.
Accomplishments
1. New invasive pest of cereals, Sipha maydis, has expanded its range into the wheat belt of the Great Plains region. ARS-Stillwater, Oklahoma scientists in collaboration with researchers with Colorado State Extension Service conducted surveys on a new invasive pest, Sipha maydis, discovered infesting oats in New Mexico in late 2014. Surveys in 2015 determined this pest was distributed in wild grasses and wheat west of the Rocky Mountains. Surveys in 2016 discovered that this pest has expanded its range east of the Rocky Mountains and is firmly established in the wheat belt of the Great Plains region.
2. Identification of sorghum (grain sorghum and forage sorghum) germplasm resistant to new invasive aphid pest of sorghum, sugarcane aphid. USDA-ARS research entomologists at Stillwater, Oklahoma in collaboration with sorghum breeders from Texas A&M, other USDA-ARS laboratories, and industry sorghum breeders identified plant resistance in both grain and forage sorghums. The WPOFC USDA-ARS laboratory also identified cross-resistance for greenbug resistance which is commercially available in grower adapted lines and this was conducted through Industry MTRA's. New sugarcane aphid resistance sources in grain sorghum has released 2 parental lines through collaboration with Texas A&M sorghum breeding program. Additionally, 2 new sources of resistance have also been discovered in forage sorghum and will be released in the near future.
3. Genetic diversity in sugarcane aphid show little genetic divergence in the U.S. and world populations. Sugarcane aphids were collected from various host plants from fifteen states within the United States and Uganda and South Africa. The genetic diversity from these populations was very low, indicating that the probability of having different host plant divergent populations (biotypes) is also low. However, more sorghum response research needs to be conducted by challenging a diverse sorghum background in order to conclusively say that no biotypes exist.
Sorghum Improvement Committee of North America; producer field days; invited presentations to the National Sorghum Producers Organization; collaborative work with Mexico Entomological Society; Sorghum and Millet Crop Germplasm Committee (CGC).
Review Publications
Li, G., Xu, X., Bai, G., Carver, B.F., Hunger, R.M., Bonman, J.M. 2016. Identification of novel powdery mildew resistance sources in wheat. Crop Science. 56(4):1817-1830.
Royer, T.A., Pendleton, B.B., Elliott, N.C., Giles, K.L. 2015. Greenbug (Hemiptera: Aphididae) biology, ecology, and management in wheat and sorghum. Journal of Integrated Pest Management. 6(1): 19 doi: 10.1093/jipm/pmv018.
Mbulwe, L., Peterson, G.C., Armstrong, J.S., Rooney, W.L. 2016. Registration of sorghum germplasm Tx3408 and Tx3409 with tolerance to sugarcane aphid [Melanaphis saccari (Zehntner)]. Journal of Plant Registrations. 10(1):51-56.
Backoulou, G.F., Elliott, N.C., Giles, K.L. 2016. Using multispectral imagery to compare the spatial pattern of injury to wheat caused by Russian wheat aphid and greenbug. Southwestern Entomologist. 41(1):1-8.
Nansen, C., Elliott, N.C. 2016. Remote sensing and reflectance profiling in entomology. Annual Review Of Entomology. 61:139-158.
Armstrong, J.S., Mornhinweg, D.W., Payton, M.E., Puterka, G.J. 2016. The discovery of resistant sources of spring barley, Hordeum vulgare ssp. spontaneum, and unique greenbug biotypes. Journal of Economic Entomology. 109(1):434-438.
