Location: Crop Genetics and Breeding Research
2021 Annual Report
Objectives
1. Characterize and improve internode length and stem maggot resistance in bermudagrass.
1A. Using RNA Sequencing, identify candidate genes that regulate internode length in bermudagrass.
1B. Develop integrated pest management strategies for mitigation of the Bermudagrass Stem Maggot (BSM).
2. Develop genetic markers and biocontrol agents to reduce root-knot nematode and aphid damage in sweet sorghum.
2A. Determine if the root-knot nematode resistance gene can be moved from Honey Drip to susceptible or moderately resistant sorghum cultivars by marker-assisted selection and thus confer or improve resistance.
2B. Identify new genetic loci for root-knot nematode resistance and develop markers associated with resistance.
2C. Investigate the use of entomopathogenic fungi to control sugarcane aphid in sorghum.
3. Assess lupin and carinata as renewable bio-based products and soil enhancement cover crops.
3A. Assess the economic and environmental impact of lupin as a winter crop cover within a summer row crop rotation.
3B. Determine the effects of Brassica carinata grown as a winter crop on soil quality and subsequent summer row crop production.
4. Develop genomic technologies for centipede grass and use those technologies to understand and improve desirable ecological and aesthetic traits for this species. Work may include, but is not limited to, water and nutrient efficiency, resilience to foot traffic, color, and pollinator support.
Approach
Objective 1: For characterization of internode length in turf bermudagrass, total ribonucleic acid (RNA) will be extracted from the leaf and stem tissue of bermudagrasses. RNA samples will be sent for library preparation and sequencing. The transcriptome will be reconstructed and differentially expressed genes will be identified and then confirmed for internode length via real-time Polymerase chain reaction (PCR). For stem maggot resistance, forage bermudagrass germplasm will be selected from the bermudagrass core collection for further evaluation for yield, quality and tolerance to Bermudagrass Stem Maggot (BSM) and tested in the field in two side by side plots (one sprayed and one not sprayed) and replicated four times in a randomized complete block design. Most tolerant lines for further analysis for yield and quality traits will be determined and used for release and use for crosses.
Objective 2: The root-knot nematode resistance gene will be moved from ‘Honey Drip’ to susceptible or moderately resistant sorghum cultivars by marker-assisted selection. Furthermore, new genetic loci for root-knot nematode resistance will be identified by creating a mapping population using a source of resistance different than ‘Honey Drip’. In collaboration with ARS fungal curator, naturally occurring entomopathogenic fungal isolates will be obtained from sugarcane aphids. Entomopathogenic fungi will be applied to susceptible sorghum to determine if these strains can control sugarcane aphids.
Objective 3: The economic and environmental impact of lupin with and without rye as a winter crop cover within a summer row crop rotation will be determined using rotating main crops of peanut and cotton over years with different cover crops during the winter (narrow leaf lupin, white lupin, white lupin + cereal rye, narrow leaf lupin + cereal rye, cereal rye, and fallow. Half the covers will be harvested and the other half rolled. Changes in soil fertility and yields will be determined. The effects of Brassica carinata grown as a winter crop on soil quality and subsequent summer row crop production an experiment will be determined by rotating carinata and rye planted as a winter cover with sorghum and soybean as rotating summer crops.
Objective 4: For the genetic mapping of desirable turf traits in centipedegrass, a genome-wide association study will be conducted using a population of approximately 300 vegetatively propagated lines replicated in the field. Morphological traits will be measured for two years after establishment. Single nucleotide polymorphisms (SNPs) will be created from each line using genotyping by sequencing and the genome of a centipedegrass line will be sequenced. SNPs will be aligned to the reference sequence and SNPs will be identified that are associated with the traits. For the identification of pollinators of centipedegrass inflorescences, a collection of centipedegrass lines will be grown in large field plots. In collaboration with an entomologist, pollinators will be documented that transit into each plot and those directly pollinating the inflorescences.
Progress Report
Objective 1A1. Differentially expressed genes among Tifgreen and its mutants were identified by ARS scientists at Tifton, Georgia.
Objective 1B1. Promising bermudagrass stem maggot (BSM) tolerant lines were tested and compared by ARS scientists at Tifton, Georgia with split-plot controls and harvested 4 times for a second year. Some lines continued to have lower BSM damage and higher yields than Tifton 85. Further years evaluation will determine the most appropriate lines to increase and use for further genetic improvement.
Objective 1B2. The second year of an 8-spray regime trail was conducted by ARS scientists at Tifton, Georgia on Alicia and Tifton 85, with significant differences found among treatments. Multiple years of this research will refine the spray recommendations for hay producers in the Southeast.
Objective 2A. ARS scientists at Tifton, Georgia determined if the root-knot nematode resistance gene can be moved from Honey Drip to susceptible or moderately resistant sorghum cultivars by marker-assisted selection and thus confer or improve resistance, progeny from the BC1F1 crosses were selfed that contain the allele from ‘Honey Drip’ in the root-knot nematode (RKN) resistance gene region.
Sub-Objective 2B. ARS scientists at Tifton, Georgia identified new genetic loci for root-knot nematode resistance and develop markers associated with resistance, this project is complete and a new genetic locus for root-knot nematode resistance was identified in sorghum. An accomplishment was reported in FY2020.
Sub-Objective 2C1. USDA-ARS Entomopathogen curator cultures entomopathogenic fungi on sugarcane aphids and identifies these fungi at least to the genus level, an ARS scientist at Tifton, Georgia has completed this work. The ARS scientists have identified sugarcane aphids that are infected with fungi of the genera Lecanicillium and Conidiobolus. ARS scientists have been sequencing gene fragments of these isolates to identify these isolates to the species level.
Sub-Objective 2C2. ARS scientists investigated the use of entomopathogenic fungi to control sugarcane aphids in grain sorghum, this project has been completed. Despite a wet summer in two locations,and none of the entomopathogenic strains, ARS scientists used as treatments reduced sugarcane aphid induced plant damage or sugarcane aphid number as compared to a water control. It was reported as an accomplishment in FY2020.
Objective 3A. During the winter of 2020-21, cover crops were re-established, maintained and harvested by ARS scientists at Tifton, Georgia to obtain biomass weights or rolled to prepare for the summer planting of peanut and cotton. The peanut and cotton crops were successfully planted for the third year of assessment after covers.
Objective 3B. Wheat (instead of rye) and carinata were planted and harvested by ARS scientists at Tifton, Georgia for the second year of the winter otation/tillage study. Soybeans were planted over all treatments after half of the plots are tilled.
Objective 4. ARS scientists at Tifton, Georgia developed genomic technologies for centipedegrass and use those technologies to understand and improve desirable ecological and aesthetic traits for this species such as pollinator support. ARS scientists have been working on conducting a GWAS experiment. 295 centipedegrass lines were selected from a diverse clonal collection and have been increased in our greenhouse. DNA has been extracted for genotyping by sequencing and the genome of a centipedegrass line has been sequenced but not yet assembled. Four reps of the 295 lines will be planted this summer.
For the aspect of how centipedegrass provides pollinator support, ARS scientists at Tifton, Georgia teamed up with entomologists and physiologists from the University of Georgia. In their first study they identified that a diverse genera of bees (13 genera) are residing in and on centipedegrass lawns seeking floral resources. These bees include sweat bees (most), long-horned bees, metallic green sweat bees, bumblebees, honeybees, leafcutter bees, and small carpenter bees. In their second study, they found that 5 genera of bees are using centipedegrass lawns as a food source as they collect pollen from centipedegrass inflorescences. These bees include primarily sweat bees, bumblebees and honeybees.
ARS scientists are also examining how the ploidy of centipedegrass impacts turf traits and water usage. ARS scientists at Tifton, Georgia created three tetraploid centipedegrass lines in 2018 using tissue culture (centipedegrass is a diploid).
Accomplishments
1. Centipedegrass, a turfgrass, provides food for pollinators. ARS scientists at Tifton, Georgia, believe an estimated 75% of the World’s flowering plants and 90% of the World’s food crops depend on pollinators to reproduce. Yet pollinator populations have been in decline worldwide for several decades and turfgrasses lawns are frequently cited as contributing to this decline. An ARS researcher in Tifton, Georgia, and colleagues sought to survey the activity of bees in centipedegrass lawns. From nine centipedegrass lawns, 173 bees were collected and found to be collecting pollen from centipedegrass inflorescences. This knowledge provided guidance to help ARS scientists at Tifton, Georgia maintain essential pollinator populations and recommend that homeowners and landscape managers apply insecticides conservatively as certain insecticides are toxic to foraging bees in lawns. This research was featured in USDA ARS Research News, USDA Radio, UGA Today, Golf Course Management Magazine May 2021 Issue, Georgia Urban Ag Council Spring 2021 edition, NPR-WUGA-Athens, Georgia, and Farm to Fork Radio. The USDA and UGA story was picked up by 32 news outlets and had a potential reach of 189 million people (Meltwater Media Tracking).
2. Sugarcane aphid damage in sorghum wax mutants are based on genetic background. ARS scientists at Tifton, Georgia, suggests since 2013, sugarcane aphids have become the major insect pest of sorghum across the United States. Sorghum varieties with genetic resistance to sugarcane aphids have been identified by ARS scientists at Tifton, Georgia, but the mechanisms of this resistance are not known. Previous studies have shown that bloomless (lacking visible wax on the leaves and stems) sorghum mutants have resistance to some biotypes of greenbug aphid. ARS scientists and their colleague at Fort Valley State University tested the response of three sorghum cultivars (P898012, Tx7078, and P954035) and their bloomless mutants to sugarcane aphids in field and greenhouse experiments. Damage from sugarcane aphid was consistently greater on the bloomless mutants of P898012 than on the normal (waxy) P898012, whereas normal versus mutant Tx7078 and P954035 were equally damaged by the aphids. It was concluded by that the waxy bloom on sorghum plants may play a limited role in sugarcane aphid resistance in some cultivars but not others, perhaps due to differences in the chemical composition of the wax in different cultivars.
3. Winter cover crops can improve summer crop yields even when harvested. ARS scientists at Tifton, Georgia, determined that legumes planted as winter covers on Southern fields can improve soil health and enhance the following summer crops by capturing nitrogen from the air. Winter covers are often tilled under or left in the field and rolled, but they could be harvested for forage. ARS scientists conducted a 5-year study to compare biomass yields of five different legumes or rye, along with fallow checks. The covers were either harvested or rolled, and were followed with high-biomass sorghum or cotton. Narrow-leaf lupin was the highest-yielding winter cover. Lupin, vetch, and winter pea covers had positive effects on summer biomass sorghum yields. Cotton lint yields were highest after lupin and vetch. Harvesting the covers reduced sorghum yields following some covers but not following lupin or vetch. Cotton yields were not affected by harvesting versus rolling of any winter covers. The study by ARS scientists suggests that growers could harvest lupin and vetch for animal feed or other uses and still improve summer row crop yields, thus increasing overall farm income and improving soil health.
Review Publications
Akter, H., Dwivedi, P., Anderson, W.F., Lamb, M.C. 2021. Economics of intercropping loblolly pine and oilseed crops for bio-jet fuel production in the United States. Agroforestry Systems. pp. 584-585. https://doi.org/10.1007/s10457-020-00584-5.
Joseph, S.V., Harris-Shultz, K.R., Jespersen, D., Vermeer, B., Julian, C. 2020. Incidence and abundance of bees and wasps in centipedegrass lawns in Georgia. Journal of Entomological Science. 55(4):547-559. https://doi.org/10.18474/0749-8004-55.4.547.
Harris-Shultz, K.R., Ni, X. 2021. A sugarcane aphid (Hemiptera: Aphididae) 'Super-clone' remains on U.S. sorghum and johnsongrass ands feeds on giant miscanthus. Journal of Entomological Science. 56(1):43-52. https://doi.org/10.18474/0749-8004-56.1.43.
De Souza, C., Lopez, Y., Munoz, P.R., Anderson, W.F., Agnol, M., Wallau, M.O., Rios, E.F. 2020. Natural genetic diversity of nutritive value traits in the genus Cynodon. Agronomy. 10(11):1729.
Shimat, J., Harris-Shultz, K.R., Jespesen, D. 2020. Evidence of pollinators foraging on centipedegrass inflorescences. Insects. 11:795. https://doi.org/10.3390/insects11110795.
Knoll, J.E., Anderson, W.F., Missaoui, A., Hale, A.L., Hanna, W.W. 2021. Biomass production and stability of five energycane cultivars at two latitudes in Georgia, USA. Agrosystems, Geosciences & Environment. 4:e20146. https://doi.org/10.1002/agg2.20146.
