Location: Crop Genetics and Breeding Research
2023 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
Under Objective 1 gene expression differences among Tifgreen and its somatic mutants MiniVerde and TifEagle and an unrelated line Tifway were examined for genes involved in dwarfism. One of the most repressed transcripts in ribonucleic acid (RNA) sequencing was a homolog to a gibberellin (GA) receptor. This transcriptional difference was confirmed in MiniVerde and TifEagle using quantitative polymerase chain reaction (PCR). Yet, application of GA to all the plants showed increased shoot elongation in all treated lines and thus other gibberellin receptors must be functional in these lines. Endogenous GA levels were measured in these lines and the most common gibberellins in plants, GA1, GA3, GA4, and GA24 were not detected in these lines. GA9 was significantly higher in MiniVerde and TifEagle than Tifgreen and Tifway with more than double the concentrations of GA9. GA53 levels were significantly higher in Tifgreen as compared to TifEagle, MiniVerde, and Tifway. Tifgreen had almost 7 times as much GA53 than TifEagle and MiniVerde and 37 times as much GA53 as Tifway. For GA29, Tifway had higher endogenous GA29 concentrations than Tifgreen, MiniVerde, and TifEagle. Thus, bermudagrass is unusual in that it lacks the common GAs seen in plants, MiniVerde and TifEagle do respond to the application of gibberellin, and endogenous levels of GA have been altered in these dwarf lines.
Under Sub-objective 1B1 two of the highest producing bermudagrass stem maggot (BSM) tolerant lines from previous work are being increased for potential release. These lines produce higher yields than the standard Tifton 85 when insecticide sprays to control BSM are not applied. Crosses with these lines are being done. The first year of crossing produced very little seed, thus the second year of crossing is being done.
Under Sub-objective 1B2 ARS Scientist at Tifton, Georgia, determined that pyrethroid effectively controls BSM on susceptible cultivars. Two years of trials have successfully determined that a single spray of pyrethroids timed by growth stage after harvest can be an effective means of controlling up to 90% of BSM damage.
In regard to Objective 2 we identified the naturally occurring entomopathogenic fungi that infect sorghum aphids on sorghum, and infected sorghum aphids were collected in 2018-2020 in Georgia, fungi were isolated and characterized morphologically and molecularly. Fungi were identified as Akanthomyces dipterigenus (formerly Lecanicillium longisporum), Neoconidiobolus thromboides, and Neoconidiobolus sp. closely related to N. stillbeus. All sequence data have been deposited to GenBank. The entomopathogen curator left the agency a couple of years ago but we’ve stayed in contact. We’ve been working on the manuscript, but it’s been moving slowly with her having another full-time job.
Sub-objective 2C2: objective completed
Under Objective 3 early economic analysis of using lupin with or without cereal rye as a harvested winter cover crop within a peanut-cotton summer rotation could increase farmers income if the lupin/rye are used as animal feed or sold as baleage. Further work is being done to determine the effects of winter cover crops on soil health.
Under Sub-objective 3B a second cycle of a sorghum/soybean summer crop trial with Brassica carinata (oilseed crop for renewable aviation fuel) or wheat as a winter crop is being completed this summer for an economic analysis to determine the best management strategies (till versus minimal till), and best winter rotations.
In regard to Objective 4 two hundred ninety-five diploid centipedegrass lines with 4 replicates were planted in Tifton, Georgia, on September 8, 2021. Last summer a large amount of data was recorded, and by Fall 2022 the grasses were about 70% grown in. The date recorded were winter survival, stigma color, anther color, flowering date, ploidy, stolon thickness, internode length, spring greenup, fall color retention, leaf length, leaf width, percent plot coverage, chlorophyll content, and stolon number. Additionally, reflectance data were recorded monthly using a multispectral camera on a drone. Genotyping by sequencing was performed and 72,523 single nucleotide polymorphisms (SNPs) were aligned to a centipedegrass reference sequence.
Accomplishments
1. Pollinators of sorghum and attraction of Hymenoptera to sorghum aphid infested sorghum plots. Pollinators are experiencing a global decline, potentially reducing both human food supply and plant diversity. To support pollinator populations, planting of nectar-rich plants with different flowering seasons is encouraged while promoting wind-pollinated plants, including grasses, is rarely recommended. However, many bees and other pollinators have often been documented collecting pollen from grasses. Sorghum, a crop primarily used for grain in the U.S., is not listed as a plant recommended to homeowners or farmers to feed pollinators despite frequent bee sightings. In an effort to quantify pollinators and beneficial insects collecting or consuming sorghum pollen, observation data were recorded by ARS researchers in Tifton, Georgia. Honeybees, bumblebees, and carpenter bees were recorded collecting sorghum pollen whereas hoverflies and earwigs were documented consuming sorghum pollen. Additionally, sorghum infested with sugarcane aphids attracts numerous flies, bees, wasps, and ants that feed on the sugary waste product of the aphids. From these two studies it was concluded that sorghum, especially when harboring sugarcane aphids, is a valuable crop for preserving pollinators and other beneficial insects. Additionally, the finding that multiple bee species utilize sorghum pollen has implications for the use of insecticides in sorghum and pollen containment especially for the newly released herbicide resistant sorghums.
2. Creation of stable tetraploid centipedegrass lines with wider leaves. Centipedegrass, grown in the southern U.S., is a low maintenance turfgrass used for home lawns, parks, and along highways. In the U.S., centipedegrass is genetically and morphologically similar, as most of the centipedegrass grown originates from a single accession from China introduced as seed collected by the USDA plant explorer Frank Meyer in 1916. To enhance morphological and genetic variability, polyploid lines were created by ARS researchers in Tifton, Georgia, using irradiation and tissue culture. After five years of continuous propagation, two lines were found to be tetraploids and one line was found to be a mixaploid (2x, 4x). The tetraploids were genotyped and were found to be unique. Six tetraploid, mixoploid, and diploid lines were evaluated in a greenhouse over two years for morphological and physiological traits. Tetraploid lines had larger stomates (pores that control gas exchange including water vapor) and wider leaves. The two tetraploid lines differed between each other for multiple morphological and physiological traits. These tetraploid centipedegrass lines may be of interest to consumers that prefer the wider leaves of St. Augustinegrass but are looking for low maintenance and chinch bug resistant alternatives.
Review Publications
De Souza, C., Canny, R.S., Sharma, N., Saha, M., Wallau, M.O., Anderson, W.F., Baxter, L., Harris-Shultz, K.R., Rios, E.F. 2023. Unraveling phenotypic diversity in Cynodon spp. germplasm for forage accumulation and nutritive value in the transition zone. Crop Science. 63:690-704. https://doi.org/10.1002/csc2.20871.
Harris-Shultz, K.R., Armstrong, J.S., Caballero, M., Hoback, W., Knoll, J.E. 2022. Insect feeding on sorghum bicolor pollen and Hymenoptera attraction to aphid-produced honeydew. Insects. 13(12). Article 1152. https://doi.org/10.3390/insects13121152.
Punnuri, S., Ayele, A., Harris-Shultz, K.R., Knoll, J.E., Coffin, A.W., Tadesse, H.K., Armstrong, J.S., Wiggins, T., Li, H., Sattler, S.E., Wallace, J. 2022. Genome-wide association mapping of resistance to the sorghum aphid in sorghum bicolor. Genomics. 114(4). Article 110408. https://doi.org/10.1016/j.ygeno.2022.110408.
Cuevas, H.E., Knoll, J.E., Harris-Shultz, K.R., Punnuri, S. 2022. Genetic mapping of sugarcane aphid resistance in sorghum line SC112-14. Crop Science. 1-9. https://doi.org/10.1002/csc2.20818.
