2012 Annual Report
1a.Objectives (from AD-416):
Sustainable production of switchgrass and other bioenergy grasses will require effective pest management. Currently we know little about the potential insect pests of the tetraploid switchgrass genotypes that are being developed as bioenergy cultivars for the Central USA. Our prior experience with greenbug-sorghum and chinchbug-turfgrasses interactions indicates that insect pests will eventually emerge on switchgrass fields. Identification of potential insect pests and detailed characterization of the plant-insect interaction will better enable us to address emergent insect pests in switchgrass production fields. Additionally, it is unclear how manipulation of plants for improved quality (for example lower lignin) will affect plant resistance to insect herbivory. Our collaborative team has recently identified the yellow sugarcane aphid, chinch bugs, and greenbugs as potential pests of switchgrass. With our combined expertise in plants and insects, we are uniquely positioned to provide significant new information that will serve as the foundation for long-term sustainable pest management strategies. The research goals of this 5 year project are to identify plants with enhanced resistance to sucking insects using defined populations of switchgrass, improve our understanding of the mechanisms, genes, proteins and metabolites contributing to the resistance, and develop sustainable pest management strategies through endogenous plant resistance. Our long-term research goals are to significantly impact the development of bioeneregy grasses with enhanced resistance to biotic stress that offer improved environmental safety and reduce human health risks.
1: Develop efficient phenotyping tools for insect resistance of switchgrass and other tall perennial grasses.
2: Understand insect resistance mechanisms among defined switchgrass populations.
3: Obtain biochemical, physiological and anatomical insights into insect-bioenergy grass interactions.
4: Define transcriptional and metabolic changes occurring in switchgrass genotypes with varying levels of insect resistance.
5: Utilize methods in RNA profiling of insects to uncover key transcriptional regulatory mechanisms that govern host range in grass-feeding insects.
1b.Approach (from AD-416):
We will take defined populations of switchgrass and investigate plant and insect responses with a wide array of complementary tools, including characterization of the resistance responses using antixenosis, antibiosis, and tolerance methodologies. Functional genomic tools will be used to define biochemical, physiological, metabolic and molecular plant defense mechanisms, and take advantage of existing switchgrass molecular resources and the pending release of a draft version of the switchgrass genome, and exploit its synteny with sorghum to identify potential genes. Traditional and molecular methods such as high-throughput DNA sequencing will be used to decipher fitness parameters for the different insects.
This work is being performed through a USDA/NIFA competitive grant awarded in October 2010 with an official start date of February 1, 2011 through January 31, 2015. For FY 12, both laboratory and greenhouse experiments were conducted.
One of the goals of the USDA-ARS Forage and Bioenergy project at Lincoln, Nebraska is to develop improved switchgrass plants for forage and bioenergy. However, it is unclear if these improved plants will be resistant to insect herbivory. The goal of this project performed through a USDA/NIFA competitive grant is to understand plant responses to herbivory to piercing-sucking insects to ultimately develop switchgrass plants with improved insect resistance.
Greenhouse experiments were continued to assess the resistance/susceptibility of 5 different switchgrass tetraploid populations to insect damage by greenbugs and the yellow sugarcane aphid. These experiments were performed with plants at the two-leaf stage and five leaf stage. Experiments are in the process of being analyzed. Consistent damage by greenbugs and yellow sugarcane aphids was observed in two populations and consistent resistance was observed in one population. Limited or no damage was seen in plants challenged with several other aphids. Work will now focus using greenbugs and the yellow sugarcane aphid to obtain plant tissues for a number of downstream uses including microscopy, biochemistry and RNA studies. In conjunction with the yearly visit by a collaborator, experimental design and collection schedule for plants were established. Leaf samples from several switchgrass genotypes identified as resistant or susceptible towards greenbug feeding were fixed and observed by scanning electron microscopy. Plants scored as resistant or susceptible have been isolated from three switchgrass populations and will be allowed to intermate in the greenhouse in 2012. Seeds obtained from these crosses will be tested for insect resistance. Plants will be maintained in the greenhouses until Spring 2013, when they will be transplanted to the field. Initial screening work has been completed and is being readied as manuscripts for peer-reviewed journal.
All team members were cognizant of the planned experiments and had approved implementation. Communication was by email and telephone between the Lead Scientist and appropriate project personnel at distant locations (University of Nebraska-Kearney; University of Nebraska-Omaha; University of Nebraska -Panhandle Research & Extension Center, Scottsbluff; University of San Diego) and by in-person meetings for project personnel located in Lincoln, NE. Two team meetings of all personnel were held in Lincoln on April 27, 2012 and on June 22, 2012.