Location: Crop Genetics and Breeding Research
2025 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, the centipedegrass genome-wide association study (GWAS), over 72,000 filtered single nucleotide polymorphisms (SNP) markers were developed and a large number of traits have been measured for four replicates of 295 accessions. These traits include three years of chlorophyll content, fall color retention, and spring green-up. We also have two years of stigma color, weekly flowering data, leaf length, leaf width, reflectance data (drone), inflorescence height, and seed head density. This fall we will measure seed yield (year 1).
Stigma color was analyzed and a single region on HIC-ASM-8 controls stigma color. Two candidate genes involved in anthocyanin accumulation were identified near the most significant SNP. Homologs of the two candidate genes in maize (b1 & r1) are functionally duplicate. Both candidate genes were sequenced from white and purple accessions and do contain insertions and SNPs that are color dependent. Thus, we suspect these two genes are involved in stigma color for centipedegrass.
For Sub-objective 1B, where we examine how cultural practices impact pollinators for three different turfgrasses, the plots were established and visual ratings on turfgrass health, flowering, and insects were taken over the summer months for the different treatments as well as morphological measurements. Additionally pollen was collected from each turfgrass to determine nutrient content. This year we are waiting for the plots to recover from last year’s drought treatment but hope to start observations and the treatments again starting on July 1, 2025.
For Sub-objective 2A, sorghum seed parents ATxARG-1, ATx631, and ATx635 were each crossed to aphid-resistant lines GTS1903, GTS1904, and GTS1905, and aphid-susceptible lines Dale and Sugar Drip in the 2024 breeding nursery. Sufficient seed from all 15 possible hybrids was recovered for testing in 2025.
For Sub-objective 2B, starter cultures of ARSEF 14358 and ARSEF 14370 (Akanthomyces dipterigenus, formerly Lecanicillium longisporum) were obtained from the ARS Collection of Entomopathogenic Fungi. Several different culture formulations were tried in order to obtain spores. Unstirred liquid Sabouraud Dextrose (SD) broth cultures with and without chitosan did not yield sufficient spores. Stirred liquid cultures (SD broth) yielded spores initially after one week, but after an additional week the spore counts actually decreased. SD agar cultures in flasks were attempted, and spores were harvested by flooding with distilled water and scraping with a rubber spatula. These cultures grew very slowly (36 d), but they did yield a reasonable concentration of spores (around = 1 x 10^6 spores/mL or around 4 x 10^5, CFU/mL). Addition of yeast extract to the stirred liquid or agar cultures generally resulted in higher spore and colony forming unit (CFU) counts. ARSEF 14358 tended to produce more spores and CFUs in culture than ARSEF 14370.
Sorghum plants were established in the greenhouse for the proposed biocontrol test, but by the time sufficient spore counts were obtained in mid-winter, there were no sorghum/sugarcane aphids available. Aphids will be collected this summer from sorghum fields so that testing can proceed.
For Sub-objective 3A, the 40 entries to be tested for cold tolerance, yield and bermudagrass stem maggot (BSM) tolerance were planted at three locations and establishment ratings were performed in the summer of 2024. Survival and vigor are being recorded in the spring of 2025 and the first clippings for yield will be performed.
For Sub-objective 3B the trial with six entries (three experimental lines plus cultivars Tifton 85, Jiggs and Russell) and two establishment methods were planted and evaluated for rates of growth. Two of the three experimental lines had a superior establishment rate by using above ground stems over traditional below ground sprigs. A new trial will be performed to determine the best herbicide treatments for establishing these lines.
For Objective 4, the division of NuSeed that works on carinata went out of business and thus Objective 4 was eliminated as no seed could be obtained.
Accomplishments
1. Discovery of naturally occurring fungi that kill sugarcane aphids. ARS researchers at Tifton, Georgia believe the invasive sugarcane/sorghum aphid has been an economically important pest to sorghum since it was first found in the U.S. in 2013. Two insecticides have been used for its control, but both have similar modes of action. A need exists for an alternative form of sugarcane aphid control in case the aphid develops pesticide resistance (which commonly occurs for insects) and for organic sorghum production. In this study, naturally occurring fungi that kill sugarcane aphids were identified from aphids infesting sorghum grown in Georgia. From morphological and molecular data, the fungi Akanthomyces dipterigenus, Neoconidiobolus thromboides, and Neoconidiobolus sp. were identified infecting sugarcane aphids from the four farms sampled. The identification of these fungi and their preservation allows the potential of a biologically based insecticide to be developed.
2. Bees utilize sorghum pollen as a food source and bumble bees can pollinate sorghum. ARS researchers at Tifton, Georgia suggest pollinators are experiencing a global decline and recommendations to increase bee populations suggest utilizing nectar-rich plants but rarely recommend plants that provide only pollen. Grasses mainly provide only pollen and at least 51 grass genera have been documented as a pollen source for bees and hover flies. In this study, insects that utilize sorghum pollen were documented and a myriad of sorghum traits were measured to determine the traits that impact insect visitation. The most numerous insect observed collecting/consuming sorghum pollen was the maize calligrapher followed by honey bees, lined earwigs, lovebugs, southern carpenter bees, common eastern bumble bees, exotic stripetails, margined soldier beetles, a signal fly, and a dusky-winged hover fly. Additionally, our results show that inflorescence (flower) abundance, plant height, and plant disease impact bee visitation in sorghum. Furthermore, field-captured bumble bees successfully fertilized sorghum in a greenhouse study, suggesting that bumblebees can pollinate sorghum flowers in field conditions. These data show that sorghum is serving as a pollinator food source and that bumblebees have the ability to pollinate the crop.
3. Discovery of a new aphid in Georgia. ARS researchers at Tifton, Georgia believe aphids are a major pest to agriculture as they damage plants by removing plant sap and serve as a vector for plant viruses. Although aphids are small in size, aphid populations can be extremely large due to their short generation times and high reproductive rates. Introduced aphids can have devastating impacts on U.S. agriculture. We report the identification of Melanaphis donacis on giant reed in Tifton, Georgia. This identification was performed by morphological and molecular analysis. Previously this aphid had only been identified in North America (U.S. in California and Mexico) as well as in Europe, Asia, Africa, and South America. The hosts, giant reed, clumping bamboos, and common reed may be impacted.
Review Publications
Yang, Y., Bera, T., Araji, H.A., Dou, F., Wilson, L.T., Rooney, W., Morrison, J., Baldwin, B., Knoll, J.E., Jifon, J., Wright, A., Odero, C., Sandhu, H.S., Hale, A.L., Mula-Michel, H.P., Wang, J. 2025. Ground-active arthropod diversity under energycane and biomass sorghum production. Insects. 16(5), 442. https://doi.org/10.3390/insects16050442.
Boatwright, L., Thudi, M., Sangiredday, M.R., Coffin, A.W., Tadesse, H.K., Vutla, S., Harris-Shultz, K.R., Knoll, J.E., Cuevas, H.E., Kumar, N., Soman, C., Schnable, J., Punnuri, S. 2024. GWAS analysis for plant height and stem diameter in sorghum using multiple phenotyping approaches. The Plant Phenome Journal. 7, e70008. https://doi.org/10.1002/ppj2.70008.
Castrillo, L., Harris-Shultz, K.R. 2024. Entomophthoralean and hypocrealean fungal pathogens of the sugarcane aphid, Melanaphis sacchari (Hemiptera: Aphididae), on sorghum in Georgia . Journal of Invertebrate Pathology. 204:108107. https://doi.org/10.1016/j.jip.2024.108107.
Davis, R.F., Harris-Shultz, K.R., Hayes, C.M., Xin, Z., Knoll, J.E. 2025. Evaluating diverse sorghum genotypes used in breeding programs for resistance to Meloidogyne incognita. Nematropica. 54:166-176.
Harris-Shultz, K.R., Halbert, S.E., Moore, M., Ni, X. 2024. First record of Melanaphis donacis (Hemiptera: Aphididae) in Georgia. Journal of Entomological Science. 59(4):524-527. https://doi.org/10.18474/JES23-105.