Location: Crop Genetics and Breeding Research
2019 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.
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: A sweet sorghum cultivar with root-knot nematode resistance will be introduced into susceptible highly productive lines by crossing. Hybrid plants with confirmed presence of the gene will be backcrossed into high productive parents. From molecular confirmation of the presence of the resistance gene plants will be inbred for a few generations. To identify new resistant sources to root-knot nematode numerous lines with reported resistance will be genotyped. Analysis will identify different resistance loci. A new resistant line will be crossed into a susceptible line and an F2 mapping population developed to identify quantitative trait linkage. To investigate the use of entomopathogenic fungi to control sugarcane aphid in sorghum, sugarcane aphids will be collected from sorghum plots, and sent to a curator for identification. Strains that cause mortality will be characterized. Entomopathogenic fungi to sugarcane aphid-infested sorghum will be tested in the field to determine if they reduce aphid populations and will reduce crop damage from aphid counts, damage ratings and grain yields.
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.
Progress Report
Ten replications of turf bermudagrass lines Tifgreen, TifEagle, Tifway, and MiniVerde were established and internode length was measured to initiate work on markers for internode length. Forage bermudagrass lines that will be tested for tolerance to bermudagrass stem maggot (BSM) and larger plots of Tifton 85 and Alicia have been established for the commencement of treatments and evaluation.
Sorghum cultivar ‘Honey Drip’ was crossed to ‘Collier’, ‘Dale’, Entry 22, GT-IR7, and ‘Top 76-6’ and the resulting seed was planted and genotyped to select for those that were hybrids. In our previous study, a major genetic quantitative trait locus (QTL) on chromosome 3 was associated with a reduction in total root-knot nematode (RKN) eggs and eggs per gram of root in the sweet sorghum cultivar Honey Drip. To develop more durable RKN resistance by combining resistance genes in sorghum lines, additional sorghum lines with RKN resistance were examined using single sequence repeat (SSR) molecular markers located in cultivar Honey Drip to potentially find alternative resistance genes. Molecular markers associated with reduced egg number and egg number per gram of root were used to genotype 10 lines from other cultivars. From this work it was determined that resistant line PI144134 may have an alternative source of resistance. This line will be selected for crossing with susceptible line Collier to create a segregating mapping population to examine the resistance genes. The entomopathogen curator Louella Castrillo obtained an Animal and Plant Health Inspection Service (APHIS) permit and inspection to receive sugarcane aphids. Once this process was completed, we shipped four shipments of aphids from four farms in Tifton Georgia last summer, 1 farm in Shorter Alabama, and 1 farm from Fort Valley, Georgia. Aphids were collected when they started to display a color change (orange) and were collected when they appeared to be healthy, at the start of the crash, during the crash, and after a crash. Two identical experiments were conducted, one at Tifton and one at Fort Valley where three entomopathogen treatments were applied: granular Beauveria bassiana strain ABNB6, Mycotrol (commercial B. bassiana liquid spray), and Ancora (commercial Isaria fumosorosea liquid spray). A positive control (Sivanto) and negative control (water) were also included. Infestation was heavy at both locations, and only Sivanto provided control of sugarcane aphid; the entomopathogen treatments were not different from water.
During the winter of 2018-19 cover crops were established, maintained and harvested 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 first year of assessment after covers. A field has been identified for the establishment of rotating rye and carinata as winter crops to assess effects on soil organic matter (SOM) in a summer rotation.
Accomplishments
1. The sugarcane aphid superclone that is attacking sorghum uses the weed Johnsongrass as an alternative host. The sugarcane aphid is a devastating pest on sorghum and has spread to all sorghum growing areas. Our previous research found the sugarcane aphids collected on sorghum from seven states and one U.S. territory in 2015 were all predominantly one clone. In this study, of a subordinate project, ARS researchers in Tifton, Georgia, genotyped sugarcane aphids from 43 locations in eight U.S. cities in 2016 from sorghum and in 2015 and 2016 from Johnsongrass to determine if the same clone predominates on sorghum and to determine if this clone is also feeding on the invasive weed Johnsongrass. We found that indeed the same ‘superclone’ is on the 2016 samples collected from sorghum and this clone was also detected on all Johnsongrass samples collected in 2015 and 2016. Thus, we have found the ‘superclone’ that feeds on sorghum also uses Johnsongrass, a weed that is pervasive in the U.S., as an alternative host. Farmers may want to eliminate Johnsongrass in areas where sorghum is grown.
