Location: Crop Genetics and Breeding Research
2024 Annual Report
Objectives
1. Improve genetic tools and pollinator-friendly management for more sustainable turfgrass systems.
1A. Identify SNPs associated with seed yield and other morphological traits in centipedegrass.
1B. Identify pollinators and beneficial insects of turfgrasses and cultural practices that enhance their abundance.
2. Improve sorghum aphid resistance and management in sweet and forage sorghum.
2A. Evaluate combining ability of new sweet sorghum lines.
2B. Test the efficacy of applied Lecanicillium fungus for sorghum aphid control.
3. Improving forage bermudagrass cultivars for cold tolerance and yield and improving availability to growers.
3A. Breed forage bermudagrass (Cynodon spp.) for cold tolerance, high yield and BSM tolerance.
3B. Improve the establishment and availability of forage bermudagrass.
4. Establishing sustainable full-year cropping systems for Southeastern Coastal Plains using a mixture of winter covers crops.
Approach
For Sub-objective 1A, single nucleotide polymorphisms (SNPs) will be identified that are associated with seed yield and morphological traits using a genome-wide association study population of 295 diverse centipedegrass lines in a replicated experiment. Genotyping-by-sequencing will be performed on all lines to generate SNPs and all traits will be measured for at least 2 years.
For Sub-objective 1B, to identify pollinators and beneficial insects of turfgrasses and cultural practices that enhance their abundance, sod will be obtained of centipedegrass, tetraploid bermudagrass, and zoysiagrass. In a split-split plot experiment, blocks will be irrigated with fertilizer, irrigated with no fertilizer, not irrigated with fertilizer, or not irrigated and no fertilizer. Mowing frequency will be weekly, every 2 weeks, and every 3 weeks. Insect type and abundance will be recorded by sweep netting, visual observations, or with cameras. Inflorescence density and height, and flowering date and period will be recorded.
For Sub-objective 2A we will produce 10 sweet sorghum hybrids by crossing three sorghum aphid resistant lines (GTS1903, GTS1904, and GTS1905) and two susceptible lines each with two seed parents. These hybrids and the parental lines will be evaluated in field trials in Georgia and Texas for yield, agronomic traits, and response to sorghum aphid.
For Sub-objective 2B we will culture 2 isolates of the fungal entomopathogen Lecanicillium longisporum in the laboratory. Fungal spores will be mixed into formulations and sprayed onto sorghum aphid infested plants in the greenhouse (year 1) and field (year 2). Water and blank formulation will be negative controls, and chemical insecticide will be the positive control. Aphid population and damage will be recorded weekly.
For Sub-objective 3A, 20 of the most cold tolerant plant introductions from previous tests and 15 introductions identified with bermudagrass stem-maggot tolerance (BSM) will be evaluated for 3 years at 3 locations for yield, BSM tolerance and cold tolerance. The 5 highest-yielding entries from the 2 northern locations and the 5 most BSM tolerant lines will be crossed and progeny evaluated at the 3 locations.
For Sub-objective 3B, 2 propagation methods (sprigs and tops) will be evaluated for establishment with current cultivars and 2 experimental forage bermudagrass lines. In year 2, a subset of 6 entries will be propagated via cut stems and tested for establishment and weed control with various herbicide treatments. The 3 best treatments will be tested against an untreated control in larger plots. From the results of these trials, a protocol will be revised to guide designated growers for establishing new fields.
For Objective 4 a replicated trial will be performed with rotating summer plots as main plots. The main plots will have three different winter sub-plot crops in rotation. Half of the winter crop biomass will be harvested and weighed, and the other half will remain on the soil as compost. We will determine the effects of rotating winter crops on the summer crops. An economic analysis using WHOLEFARM will determine the best rotations for economic returns to growers.
Progress Report
For Sub-objective 1A, 2-year data for chlorophyll content, fall color retention, stigma color, leaf length, leaf width, spring green up, and reflectance data were collected from the centipede Genome-wide association study (GWAS) population. Stigma color was analyzed first and markers on one chromosome were highly associated with stigma color for both years. The most associated single nucleotide polymorphisms (SNPs) were near two genes involved in chlorophyll biosynthesis. One candidate gene was amplified and sequenced and found to contain a large insertion in the accessions with white stigmas.
For Sub-objective 1B, the field was fumigated and then sod of common centipede, ‘Empire’ Zoysia, and ‘Celebration’ bermudagrass was sodded to form 180 6.5 ft x 6 ft squares on 6/1/23. Plots were allowed to grow in and then data was collected. Mowing frequency was varied from a weekly, biweekly, or triweekly (every 3 weeks). Insects collecting or consuming turfgrass pollen were recorded per plot from 8/28/23-10/10/23. Morphological measurements per plot were chlorophyll content, leaf length, leaf width, inflorescence height, inflorescence density. Pollen was collected several times from these plots and with expertise from ARS in Tucson, Arizona pollen protein and lipid content was measured from the three different turfgrasses.
For Sub-objective 2A, seven seed parent lines (A/B pairs) of sorghum were acquired from another ARS location and were planted in the field in 2023 for initial evaluation and increase. Among these, A/BTxARG-1, A/BTx631, and A/BTx635 had the best performance in the field and were selected for crossing in the 2024 nursery.
For Sub-objective 2B, with proper permits obtained, we have requested cultures of ARSEF 14358 and ARSEF 14370 (Akanthomyces dipterigenus, formerly Lecanicillium longisporum) from the ARS Collection of Entomopathogenic Fungi. We have not yet received these cultures.
For Sub-objective 3A, plant material was established in pots in the greenhouse during the fall of 2023. This material will be transplanted to the field in the summer of 2024.
For Sub-objective 3B, two propagation methods were evaluated for three current forage bermudagrass cultivars and three experimental lines. The experimental lines established well by using either method (above-ground stems or below ground sprigs). Further trials are underway.
For Objective 4 core soil samples have been taken and will be evaluated for baseline carbon and nitrogen. Summer crops (peanut, cotton and sorghum plots) have been planted.
The field portion of the subordinate project ‘Sustainable Herbaceous Energy Crops for the Southeast’ has been completed. At Tifton, Georgia, three genotypes of biomass sorghum were grown for four years, three genotypes of energycane were grown for three years, and biomass yields were measured. Each crop was sampled regularly during the growing season for stalk count, leaf and stem masses, and concentration of nitrogen and other nutrients. Deep (approx. 1 meter) soil cores were taken annually to assess changes in soil carbon and other soil properties under bioenergy crop production. Soil cores from a ‘local reference crop’, in this case corn, were also sampled for comparison. Shallow (30 cm) soil samples were also collected annually to assess changes in the soil microbiome. Ground-active invertebrates were monitored during the growing season by pitfall traps. Surface runoff and deep percolating water were collected after rain events to monitor cycling of nitrogen and other nutrients. Greenhouse gas emissions from the soil were monitored using static chambers, collected at regular intervals throughout the growing seasons. Post-harvest storage trials of biomass in tarped piles (aerobic storage) or in bale bags (anaerobic storage) were conducted twice. Stored biomass was sampled after three, six, and nine months of storage for biomass loss and fiber composition. Data from Tifton, Georgia and from other locations throughout the Southeast are being compiled and analyzed.
Accomplishments
1. Pearl millet is a pollinator magnet. Bees provide the most pollinator services and are in decline due to loss of floral abundance and diversity, loss in suitable habitat, long-term exposure to pesticides, species introductions, and infection by parasites and pathogens. Human efforts to aide bees focus on the planting of nectar rich plants but rarely promote wind pollinated crops that mainly provide only pollen. Yet bees and hoverflies are frequently seen collecting or consuming pollen from grasses. Many growers of pearl millet note the large number of bees that are attracted to this crop during flowering. To document this, ARS researchers at Tifton, Georgia identified insects that collect or consume ‘Tift Long-Headed Bulk’ pearl millet pollen and determined if plant traits impact insect number. We found honeybees were the most abundant insect followed by lined earwigs, maize calligraphers, two-spotted longhorn bees, banded cucumber beetles, exotic stripetails, common eastern bumblebees, American bumblebees (threatened species), sweat bees, and an eastern band-winged hoverfly. More maize calligraphers were seen on shorter plants as compared to taller plants. Thus, ‘Tift Long-Headed Bulk’ pearl millet can serve as a multi-week food source for native and non-native pollinators which is useful to growers and homeowners interested in protecting/providing food resources to beneficial insects. The ARS Office of Communications will release a news brief during National Pollinator Week (June 17-23, 2024) featuring this research.
Review Publications
Knoll, J.E., Uchimiya, S.M., Hayes, C.M., Punnuri, S.M., Harris-Shultz, K.R., Smith, J.S. 2023. Registration of three sweet sorghum lines with high tolerance to sorghum aphid (Melanaphis sorghi). Journal of Plant Registrations. 17:551-560. https://doi.org/10.1002/plr2.20310.
Harris-Shultz, K.R., O'Hearn, J.S., Knoll, J.E., Clem, C.S. 2024. Insects foraging on pearl millet, Cenchrus americanus, pollen. Journal of Entomological Science. 59(4):506-514. https://doi.org/10.18474/JES23-91.
Baxter, L.L., Anderson, W.F., Hudson, W.G., Rios, E.F., Bowling, C.H., Burt, J.C. 2024. Improved management of the bermudagrass stem maggot. Crop, Forage & Turfgrass Management. 10:e20269. https://doi.org/10.1002/cft2.20269.