Location: Floral and Nursery Plants Research
2022 Annual Report
Objectives
1. Enhance marker resources and diversity assessment in the genus Danthonia. (NP215 2D)
Sub-objective 1.A: Utilize induced mutations to study D.spicata reproductive biology.
Sub-objective 1.B: Evaluate native Danthonia species genetic diversity and ploidy.
2. Characterize the phytobiome of native and newly established Danthonia populations and correlate them with biotic and abiotic stress resistance. (NP215 2D)
Sub-objective 2.A: Evaluate the genetic diversity of Atkinsonella hypoxylon associated with D. spicata.
Sub-objective 2.B: Utilize culture-dependent fungal isolation to identify the endophytic fungal populations of D. spicata from diverse locations.
Subobjective 2.C: Determine the contribution of the Danthonia phytobiome on ecosystem services in the DC metropolitan urban environment.
3. Determine the impacts of stress (heat and drought) on Danthonia gene expression and reproductive biology. (NP215 2D)
4. Characterize the phytobiome of turf species and determine their role in disease resistance in the warm humid climate of the mid-Atlantic U.S. The research will investigate the contribution of the turf phytobiome to ecosystem services and disease resistance.
Approach
The native grass Danthonia spicata has a number of characteristics that make it well suited for use as a low input turf in the U.S. mid-Atlantic region. The primary drawback for utilization is poor seed production potential and very limited genetic diversity. For example, D. spicata seed production suffers from seed shattering, a common characteristic of unimproved grasses, but its lack of genetic diversity combined with its unusual reproductive characteristics do not provide options for improving seed production through conventional breeding approaches.
The unusual reproductive characteristics of D. spicata include anther developmental arrest at a very early stage and precocious seed production without any evidence of fertilization. Progeny plants exhibit extreme uniformity, and SSR markers scored on progeny populations are monomorphic. Although apomixis would be a possible reproductive strategy, apomicts typically exhibit high levels of fixed heterozygosity due to premeiotic embryo formation. Post-meiotic automixis, either through the formation of a restitution nucleus or an endomitotic event, are additional possible mechanisms. To test the various reproductive strategies genetically and to generate variation for plant improvement requires the creation of polymorphisms that can be followed through meiosis; this will be done through mutation breeding.
The genus Danthonia includes a number of species that have been recognized as native grasses of the U.S. The existence of an unusual reproductive biology in the genus and the fact that a number of the proposed species grow in close proximity suggests that some of the species may simply be variants of a single species. One mechanism that would support the current species designations is polyploidy. Currently no data is available on the ploidy levels of the native Danthonia species. A second factor that would support the species designations is large amounts of genetic variation between the described species; this will be tested using Simple Sequence Repeat (SSR) markers.
Atkinsonella hypoxylon (Clavicipitaceae, tribe Balansieae) is an Ascomycete that has been reported to grow epiphytically and endophytically on grasses in the genus Danthonia. Genetic diversity assessments of A. hypoxylon have been completed; however, they were conducted using isozyme technology and no Internal Transcribed Spacer (ITS) data was obtained to confirm isolate taxonomy. The genome sequence of A. hypoxylon has been determined, making Simple Sequence Repeat (SSR) marker development possible; currently our lab has approximately 20 functional SSR primer pairs that have been tested on isolates from 4 locations. Additionally, all isolates we have examined exhibit multiple loci with 2 alleles. This multiallelic state in what is expected to be haploid hyphae has also been reported in Epichloe festucae and could be due to multistrain infections of the plants. ITS cloning will be utilized to determine if Danthonia plants harbor multiple symbiotic fungi.
Progress Report
Danthonia spicata is a native low input grass that has potential as a new turf species. D spicata harbors an epiphyte, Atkinsonella hypoxylon, that may play a significant role in the plant’s ability to persist under low input conditions. Field observations suggest that the epiphyte may be significantly impacted by UV light exposure. This hypothesis would explain why D. spicata is generally found under tree cover; when trees are removed, D. spicata populations do not persist. We refocused our germplasm collection efforts on D. spicata plants exposed to full sunlight. New full-sun germplasm of D. spicata has been identified and this material will be tested for its ability to persist under full sun conditions.
Creeping bentgrass, Agrostis stolonifera, and colonial bentgrass, A. capillaris, are cool season turfgrass species well adapted for utilization on golf courses. Natural stands of creeping bentgrass are often found in wetland areas and exhibit very poor tolerance to dry soils. Colonial bentgrass is frequently found in drier habitats and can go dormant and recover quickly under water deficit stress. It is also resistant to dollar spot disease, which is the most economically important fungal disease of turfgrass. We developed and established an interspecific mapping population by crossing creeping and colonial bentgrass. The population consists of approximately 300 plants and has been replicated in the field and greenhouse for evaluating genetic variations in drought and disease resistance. Mapping work on this population will provide useful data on dollar spot resistance and drought tolerance. In addition, the genetic mechanisms involved with colonial bentgrass dormancy will be studied.
To understand the genetic diversity of the Agrostis genus more fully, a germplasm panel was established consisting of nearly 1000 plants from approximately 50 different creeping, colonial, and velvet bentgrass cultivars. This plant material will be utilized in phenotyping experiments and to evaluate the variability that exists at important genetic loci.
A detailed investigation of temporal and spatial dynamics of disease/drought progression is necessary to evaluate genetic variations in these mapping populations and diversity panels. Recent advances in high-throughput imaging technologies such as hyperspectral imaging systems (HIS) along with multi-omics-driven technologies such as molecular detection assays, and metabolite/enzyme profiling can greatly enhance the speed, efficiency, and accuracy of phenotyping of visual traits and symptoms triggered by abiotic and biotic stresses. We began to develop a GPS-based, Deep Learning (DL)/Artificial intelligence (AI)-enabled multimodal imaging interface to effectively monitor drought and disease outbreak and progression. Temporal and spatial observations at anatomical, physiological, molecular, and biochemical levels will provide multiple layers of information that can be interconnected to build a convolution neural network (CNN) for DL. After filtering multiple layers of phenotypic traits, the network will try to condense the information down into a final prediction. DL is a new breakthrough technology that can go through multiple layers of information to analyze and classify data to enable accurate and precise detection of plant phenotypes.
Accomplishments
Review Publications
Amundsen, K., Warnke, S.E., Bushman, B.S., Robbins, M.D., Martin, R.C., Harris-Shultz, K.R. 2020. Colonial bentgrass transcripts-expression differences compared with creeping bentgrass in response to water-deficit stress. 61(3):2135-2147. Crop Science. https://doi.org/10.1002/csc2.20437.
Bushman, B.S., Robbins, M.D., Warnke, S.E., Martin, R.C., Harris-Shultz, K.R., Amundsen, K.E. 2020. Gene expression differences for drought stress response in cool-season turfgrasses. International Turfgrass Society Research Journal. https://doi.org/10.1002/its2.25.
Warnke, S.E. 2020. PCR-based detection of the epibiotic fungus Atkinsonella hypoxylon within its host grass Danthonia spicata. Crop Science. 60:1660-1665. https://doi.org/10.1002/csc2.20149.
