Location: Crop Genetics and Breeding Research
2020 Annual Report
Accomplishments
1. Identification of a new root-knot nematode resistance QTL in sorghum. The southern root-knot nematode (RKN) is the most common and destructive nematode species with a wide host range. Found in agricultural regions worldwide, farmers manage root-knot nematodes by applying nematicides, crop rotation, and the use of resistant cultivars. Sorghum is highly tolerant of RKN but some cultivars are able to support increased RKN population numbers. Higher numbers of RKN in the soil increases the risk of damage to subsequently planted susceptible crops. ARS researchers at Tifton, Georgia, previously identified a major quantitative trail locus (QTL) for RKN resistance on sorghum Chr. 3 but for a cultivar to maintain durable resistance, multiple resistance genes should be present in a plant. In this study these ARS researchers from Tifton, Georgia, and collaborators from the University of Georgia identified a new source of root-knot nematode resistance, created a genetic mapping population, and identified genetic markers associated with egg number and egg number per g of root. They found a single major QTL on Chr. 5 is associated with resistance to RKN. These regions on Chr. 5 and Chr. 3, from their respective parents, can be moved into elite, high-yielding sorghum by crossing for durable RKN resistance.
2. Survey of pollinating insects in centipedegrass lawns. In the U.S., turfgrasses are a major component of the landscape covering over 160,000 km2. Centipedegrass is a warm-season turfgrass that is often grown in the southeastern U.S. Recently honeybees were documented collecting pollen from the inflorescences of centipedegrass. With the decline of pollinators in abundance and diversity worldwide, ARS researchers in Tifton, Georgia, and scientists from the University of Georgia sought to survey the activity of bees in centipedegrass lawns in central and southern Georgia using nine lawns. 173 bees were collected from centipedegrass lawns of which 79% were Lasioglossum spp. (sweat bees), 7% were Halictus spp., and 4% were Melissodes spp. (long-horned bees). Other bees collected were Augochlorella spp. (sweat bees), Agapostemoa spp. (metallic green sweat bees), Bombus spp. (bumble bees), Megachile (leafcutter bees), Apis, Peponapis (squash bees), Ceratina (small carpenter bees), Ptilothrix, Svastra (long-horned bees), and Nomia spp. (sweat bees). Thus, our data shows that diverse genera of bees are residing in or in close proximity to lawns and foraging in and around the lawns seeking floral resources. With the knowledge that a large number of bees are present in centipedegrass lawns, homeowners and landscape managers should apply insecticides conservatively as certain insecticides are toxic to foraging bees in lawns.
3. Testing of entomopathogens to control sugarcane aphid in sorghum. The sugarcane aphid outbreak on U.S. sorghum began in 2013 near Beaumont, Texas, and by 2018 it spread to 21 states. Spreading by largely a single ‘super-clone’, this pest caused a yield decline on susceptible sorghum hybrids that ranged from 50-100% in infested fields. To control the sugarcane aphid, two insecticides are used in the U.S. with the same mode of action. As the number of insecticides available are limited to control sugarcane aphid on sorghum, ARS researchers in Tifton, Georgia, in collaboration with Fort Valley State University and Wingate University sought to determine if fungi that are pathogens to insects can be applied to reduce the damage caused by sugarcane aphids. Two strains of Beauveria bassiana and one strain of Isaria fumosorosea as well as water (negative control) and an insecticide Sivanto (positive control) were applied to a susceptible sorghum hybrid in field plots located in Tifton and Fort Valley, Georgia in 2018. As compared to the treatment with water, only the plots treated with Sivanto had less aphids and plant damage as well as more grain yield. Thus, these strains of fungi were ineffective for controlling the sugarcane aphid under our field conditions. This information is useful to growers and researchers as two of the strains used are commercially available and sold as Mycotrol and Ancora.
4. Population genetics of sugarcane aphids in North America. The sugarcane aphid has been a perennial pest to sorghum in the U.S. since 2013. Sugarcane aphids, although small in size, can build to tremendous numbers with 10,000 aphids being recorded on a single sorghum plant. Plant damage ranges from leaf pigmentation to plant death. ARS researchers in Tifton, Georgia, with the aid of colleagues who collected samples, discovered that the sugarcane aphids that were spreading in the U.S. on sorghum from 2013-2017 were predominantly one super-clone (one genotype). In this study sugarcane aphids were collected from seven states and one territory from Columbus grass (Sorghum almum Parodi), Johnsongrass, sorghum, sugarcane and giant miscanthus from 2013-2019 and were genotyped using genetic markers. They found that the super-clone was still pervasive in the U.S. in 2018 and that it is using giant miscanthus as an alternate host which can contribute to the pervasiveness of the pest through the cropping years.
5. Napier grass (Elephantgrass) as a bioenergy feedstock. Napier grass has the highest biomass productivity of any grass for cropping in the southeastern United States. This was a case study using Napier grass for production of bioethanol. ARS researchers in Tifton, Georgia, and Peoria, Illinois, determined the amount of bio-ethanol that would be produced under different yearly harvest schedules. Napier grass was grown for 5 years using low-input systems on fields in the Southeast. As long as the crop was fertilized (May) and harvested (December) production was consistent. In contrast, two cutting times per year (June and then again in December) led to dramatic declines in production beginning in Year 3. The 2nd and 4th year samples were analyzed for chemical composition and processed to ethanol using an ARS developed yeast suitable for this purpose. The ethanol yield per hectare was 9.0 and 12.8 cubic meters in the 2nd and 4th growing season, respectively. This will out-yield a corn production field at 180 bu/acre by a considerable margin. As such, this manuscript demonstrates that Napier grass cropped with a low-input system is suitable for production of advanced ethanol fuel but should only be harvested once per year for maximum ethanol production. This work will be of interest to the bioethanol producers and farmers located in the Southeast.
Review Publications
Bunphan, D., Knoll, J.E., Anderson, W.F. 2019. Yields of sesame vary dramatically under rain-fed conditions on marginal lands in Thailand. Australian Journal of Crop Science. 13(12):2075-2085.
Harris-Shultz, K.R., Armstrong, J.S., Jacobson, A. 2019. Invasive cereal aphids of North America: Biotypes, genetic variation, management, and lessons learned. Trends in Entomology. 15:99-122.
Paudyal, S., Armstrong, J.S., Harris-Shultz, K.R., Wang, H., Giles, K.L., Rott, P.C., Payton, M.E. 2019. Evidence of host plant specialization among the U.S. sugarcane aphid (Hemiptera: Aphididae) genotypes. Trends in Entomology. 15:47-58.
Dien, B.S., Anderson, W.F., Cheng, M., Knoll, J.E., Lamb, M., O Bryan, P.J., Singh, V., Sorensen, R.B., Strickland, T.C., Slininger, P.J. 2020. Field productivities of Napier grass for production of sugars and ethanol. ACS Sustainable Chemistry & Engineering. 8(4):2052-2060. https://dx.doi.org/10.1021/acssuschemeng.9b06637.
Armstrong, J.S., Harris-Shultz, K.R., Ni, X., Wang, H., Knoll, J.E., Anderson, W.F. 2019. Utilizing biodemographic indices to identify perennial bioenergy grasses as sugarcane aphid (Hemiptera: Aphididae) host plants. Trends in Entomology. 15:1-14.
Harris-Shultz, K.R., Davis, R.F., Wallace, J., Knoll, J.E., Wang, H. 2019. A novel QTL for root-knot nematode resistance is identified from a South African sweet sorghum line. Phytopathology. 109(6):1011-1017. https://doi.org/10.1094/PHYTO-11-18-0433-R.
