Location:
2018 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 Objective 1A, in FY 2017, ARS aphid colony room and genetics lab were modified and sealed, for APHIS aphid quarantine approval which was granted in April made this study possible. Field studies in the fall 2017 identified sites that provided wild grass hosts near cultivated wheat to compare biotypic population differences in Russian wheat aphid (RWA). Only sites in western Oklahoma were sampled and colonies are currently being evaluated for initial biotype differences. Other areas were not sampled due to pending retirement of a scientist assigned to this project. During the RWA study, critical information on the distribution and host range of new invasive aphid species, Sipha maydis, was also collected from FY 2015-2018 and a paper will be submitted this FY. In addition, research has been completed on identifying resistance in barley to S. maydis that found cross-resistance in some RWA resistant germplasm. With the identification of resistance mechanisms to RWA in a new resistance gene in wheat, both studies on resistance in barley and wheat are completed, analyzed, and manuscripts are in preparation.
Under Objective 1B, over 10,000 wheat accessions were screened for greenbug resistance, a few resistant plants from a U.S. breeding line PI 595379 were identified. Bioassays suggested that the reselection line PI 595379-1 was highly resistant to greenbug biotypes B, C, E, and I. Using a set of F2:3 lines derived from the cross PI 595379-1 x PI 243735, we mapped the greenbug resistance gene in PI 595379-1, designated Gb595379, to the long arm of chromosome 7D, where Gb3 and Gb7 were harbored. Given that greenbug biotype B was virulent to Gb3 and Gb7, Gb595379 is a new gene/allele. We further made two crosses to derive segregating populations for allelism tests aimed at determining the relationships of Gb595379 with Gb3 and Gb7. We expect to complete allelism tests in 2019.
Under Objective 2A, the mechanisms of resistance for several sugarcane aphid sorghum (SCA) lines has been identified, described and published in peer review journal articles through graduate student research and cooperation and collaboration with other USDA Laboratories and University sorghum breeders and geneticists. Another 3,000 germplasm sources from the Sorghum Conversion Program were initially screened and identified over 400 lines that showed promise and will be further evaluated. Currently, all 400 sorghum germplasm entries are currently planted in the field at Texas A&M Lubbock, Texas and are currently being be field evaluated for SCA resistance. To date, a total of 33 sugarcane aphid resistant sorghum germplasm have been released through the journal of plant registrations in cooperation with the USDA Laboratory in Lubbock, Texas and through two sorghum breeders from Texas A&M University.
Under Objective 2B, during 2018 a sugarcane aphid (SCA) isolate collected from sugarcane in Florida was compared to the Texas sorghum type that caused severe economic loss in sorghum throughout the USA beginning in 2013. The sugarcane/Florida isolate (MLL-D) and was genetically different when compare to the Texas sorghum (MLL-F) type through gel electrophoresis and when exposed to a series of sorghum and sorghum relatives used as host differentials. This was further verified from research recently published where several U.S. collections were genetically compared to a set of global collections outside the USA. It was found that the two USA biotypes (MLL-D and MLL-F) were different from biotypes MLL-A in Africa, MLL-B in Australia, MLL-C in South America, Caribbean, East Africa and Indian Ocean islands, and MLL-E in China. The complete genome of the sugarcane aphid biotype MLL-F was sequenced by collaborative effort between ARS-USDA, Stillwater, and other USDA laboratories in Nebraska, Hawaii and Iowa.
Under Objective 3A, we were unable to obtain multispectral imagery of sugarcane aphid infested sorghum fields due to lack of availability of sugarcane aphid infested sorghum fields. However, data from previous years of this project were analyzed to (1) demonstrate that airborne multispectral imagery be used to quantify the pattern of sugarcane aphid infestations at a subfield level, and (2) quantify temporal change in spatial pattern of sugarcane aphid infestations at the field scale.
Under Objective 3B, nine greenhouse grown plants (wheat or canola) infested with bird cherry-oat aphids (wheat) or turnip aphids (canola) were placed in each of eight study fields of wheat and canola. The study was repeated twice during the growing season, once in late October and a second time in mid-March. The plants were left in the field for three days and then caged and returned to the greenhouse to allow any parasitoids to develop to the pupal stage. Adult parasitoids from plants were counted and identified to species. In addition, a D-Vac sampler was used to obtain an estimate of the density of aphids in each field on approximately the day plants were placed in that field. Parasitoid exclusion cage experiments were conducted in each wheat field in late October and again in mid-March in each wheat and canola field. The experiments ran for four weeks in both autumn and spring. At the end of four weeks the foliage from within each cage was cut and transported to the laboratory. The numbers of aphids and mummified aphids were determined for each cage.
Under Objective 4, bioassays on dsRNA constructs for aphid control did not achieve mortalities over 20%. Due to the pending retirement of the Scientist, new constructs were not made in order to pursue salivary comparisons of two sugarcane aphid biotypes, MLL-F on sorghum and MLL-D on sugarcane which our project has been provided extra funding by ONP to pursue. Salivary fluids have been collected and are currently being concentrated for proteomic analysis by LC-MS this FY to determine both proteomic and genetic differences between these biotypes.
Accomplishments
Review Publications
Nibouche, S., Costet, L., Holt, J.R., Jacobson, A., Pedarcik, A., Sadeyen, J., Armstrong, J.S., Peterson, G.C., Mclaren, N., Medina, R.F. 2018. Invasion of sorghum in the Americas by a new sugarcane aphid (Melanaphis sacchari) superclone. PLoS One. 13(4): e0196124. https://doi.org.10.1371/journal.pone.0196124.
Mornhinweg, D.W., Armstrong, J.S., Puterka, G.J. 2017. New greenbug resistant sources in winter barley, Hordeum vulgare (L.). Southwestern Entomologist. 42(3):619-626.
Limaje, A., Hayes, C., Armstrong, J.S., Hoback, W., Zarrabi, A., Paudyal, S., Burke, J. 2018. Antibiosis and tolerance discovered in USDA-ARS sorghums resistant to the sugarcane aphid (Hemiptera: Aphididae). Journal of Entomological Science. 53(2):230-241. https://doi.org/10.18474/jes17-70.1.
Li, G., Xu, X., Carver, B.F., Guo, P., Puterka, G.J. 2018. Dn10, a new gene conferring resistance to Russian wheat aphid biotype 2 in Iranian wheat landrace PI 682675. Crop Science. 58(3):1219-1225. https://doi.org/10.2135/cropsci2017.10.0649.
Elliott, N.C., Brewer, M.J., Giles, K.L. 2018. Landscape context affects aphid parasitism by Lysiphlebus testaceipes (Hymenoptera: Aphidiinae) in wheat fields. Environmental Entomology. 47(4):803-811. https://doi.org/10.1093/ee/nvy035.
Backoulou, G.F., Elliott, N.C., Giles, K.L., Alves, T.M., Brewer, M.J., Starek, M. 2018. Using multispectral imagery to map spatially variable sugarcane aphid infestations in sorghum. Southwestern Entomologist. 43(1):37-44. https://doi.org/10.3958/059.043.0122.
