Location: National Peanut Research Laboratory
2022 Annual Report
Objectives
Objective 1. Characterize peanut pathogens, host responses, and host-plant interactions, including diversity of plant invasion and plant health genes, and use genomic and transcriptomic knowledge for discovery and development of novel methods or technologies to control diseases.
Objective 2. Identify, characterize, and evaluate peanut genes involved in disease resistance and drought tolerance, including discovery and elucidation of agriculturally-relevant candidate genes, and work with breeders to facilitate implementation into breeding programs.
Objective 3: Conduct research to develop and assay novel high-throughput pre-harvest aflatoxin resistance screening methods, identify genes, and determine their functions and expression, develop molecular markers with mapping populations, and work with breeders to develop aflatoxin-resistant peanut varieties. (NP 301, C1, PS1A and PS1B).
Objective 4. Determine the physiological mechanisms that link Aspergillus infection with aflatoxin contamination (NP 303, C2, PS 2A).
Objective 5. Understanding the pathway in aspergillus invasion (collaborative effort with FVSU utilizing their scanning electron microscope abilities to understand changes in hull structure under varying environmental conditions), determine impact of Laccase enzymes on hull degradation (NP 303, C2, PS 2A).
Objective 6. Work with breeders to develop varieties with resistance to aflatoxin (NP 301 C1, PS 1A).
Approach
Double strand RNA (dsRNA) that targets aflatoxin synthesis can be used as a therapeutic control of mycotoxins in peanut without genetic transformation. Knowing the genetic makeup of peanut pathogens (Cercospora arachidicola, Cercosporidium personatum, Thecaphora frezzi, Aspergillus (A.) niger, A. flavus and A. parasiticus) allows for a better disease management and longer effectiveness of control. Identification and validation of molecular markers associated with biotic (early and late leaf spot, peanut smut, crown rot disease, mycotoxin producing fungi), and abiotic (drought) stress resistance in wild peanuts and land races will accelerate breeding programs. Analysis and non-GMO manipulation of gene expression, physiology, microRNA expression, and changes in methylation patterns, both of the plant seed as of Aspergillus during the process of infection, can point to resistance genes or other desirable seed response relevant to the control of aflatoxins. Aspergillus Laccase enzymes are a potentially important factor in pathogenicity, studying the activity of these enzymes on hull degradation/penetration in relation to the varying composition of hulls depending on cultivar and maturity, can lead to develop tools to interfere/block the action of laccases and hence seed invasion by Aspergillus, this work will incorporate the assistance of Scientists in our Unit who have expertise in mechanical resistance of hulls. Collaborating with other research projects in our Unit, we will provide the infrastructure support for large scale screening of germplasm to be incorporated in our pre-breeding program.
Progress Report
We determined that peanut phytoalexins affect the level of expression and processing of aflatoxin-biosynthesis genes in Aspergillus flavus. Peanut seeds produce many phytoalexins, varying with germplasm and time after fungal infection. Understanding how each of those phytoalexins prevents aflatoxin accumulation can guide the breeders to seek germplasms that produce the most useful phytoalexins. We have sequenced the genome of the peanut smut fungal pathogen, Thecaphora frezii, its draft genome was uploaded to the GenBank database, and a manuscript was submitted for publication. Peanut smut disease is currently endemic to South America where it causes up to 50 % losses; in the U.S. We are actively gathering information about the pathogen and resistant peanut germplasm to protect the peanut industry and be prepared in the event of an outbreak. We completed for the first time an analysis of the genetic diversity of Aspergillus section Flavi colonizing peanut seeds in Ethiopia, the paper was published. As new technologies are being developed to target specific genome sequences of pathogens; the work on genetic diversity of Aspergillus in Ethiopia provides information to identify the most common genotypes to target.
During 2021, eight drought tolerant lines that had been identified in 2020 and several susceptible lines were re-evaluated using rainout shelters to confirm yield and physiological responses. These were planted as single plants and high density (6 seed per ft) planting. Physiological measurements and leaf samplings were conducted every week during drought treatment (5 weeks of drought and 1 week of recovery after re-irrigation). Pod count and “clean” yield weight were taken after pod curing procedure. Data are being analyzed and compared to data from 2020 to detect possible correlations. This information will assist breeders in selecting the desired parent lines to generate new recombinant inbred lines that will associate high yield with physiological traits.
During 2021, a total of 1,500 breeding progeny lines from F2 to F7 were planted in two planting days at Headland, Alabama. The goal was to select for high yield, leaf spot and Tomato Spotted Wilt Virus (TSWV) resistance, as well as drought tolerance. Fifty-two advanced lines have been tested at four locations in Georgia and Alabama for yield and disease evaluation trials. Two advanced breeding lines ‘AU18-35’ and ‘AU18-53’ were tested for a second time in Uniform Peanut Performance Tests (UPPT) in 2021. Advanced breeding line named ‘AU14-34’ was released as ‘AU-Barkley’.
Accomplishments
1. New functions of phytoalexins. In search for solving aflatoxin contamination of seeds, we must understand the interaction between peanut and the fungus that produces the mycotoxins. ARS scientists at Dawson, Georgia, identified for the first time the effect that some peanut phytoalexins have on the expression and processing of aflatoxin biosynthesis genes in Aspergillus flavus. The information can be used when analyzing gene expression data of the Aspergillus/peanut seed interaction to seek the more promising peanut germplasm for breeding.
2. Cultivars with drought tolerance. As a consequence of global warming, more frequent and severe droughts are occurring in the peanut growing area. ARS scientists at Dawson, Georgia, identified eight peanut cultivars that showed higher yields than the drought tolerant control line (C76-16) under middle season drought treatment, when compared to a drought susceptible line (AP-3) that shows the lowest yield. From different physiological measurements, leaf photosynthesis and stomatal conductance (leaf transpiration) rates are highly correlated with yield. This information will assist peanut breeders to select drought tolerant lines based on physiological measurements to maintain high yield under drought stress.
3. Advanced peanut breeding line release. In late 2021, the advanced breeding line named ‘AU14-34’ was released as ‘AU-Barkley’. This is a Virginia-type peanut with prostrate growth habit and a main stem. AU-Barkley is high-yielding, resistant to tomato spotted wilt virus resistant, tolerant to leaf spot diseases, has a high grade, and superior shelling characteristics. In addition, it has high oleic fatty acid content desirable characteristic for storage and good flavor.
Review Publications
Arias De Ares, R.S., Orner, V.A., Martinez-Castillo, J., Sobolev, V. 2021. Aspergillus section Flavi, need for a robust taxonomy. Microbiology Resource Announcements. 10:48 e00784-21. https://doi.org/10.1128/MRA.00784-21.
Li, L., Cui, S., Dang, P.M., Yang, X., Liu, L., Chen, C. 2022. GWAS and bulked segregant analysis reveal the loci controlling growth habit-related traits in cultivated peanut (Arachis hypogaea L.). Biomed Central (BMC) Genomics. 23,403. https://doi.org/10.1186/s12864-022-08640-3.
Massa, A.N., Arias De Ares, R.S., Sorensen, R.B., Sobolev, V., Tallury, S.P., Stalker, T.S., Lamb, M.C. 2021. Evaluation of leaf spot resistance in wild arachis species of section arachis. Peanut Science. 48(2):68-75. https://doi.org/10.3146/PS20-25.1.
Mohammed, A., Faustinelli, P.C., Chala, A., Dejene, M., Fininsa, C., Ojiewo, C., Ayalew, A., Hoisington, D., Sobolev, V., Martinez-Castillo, J., Arias De Ares, R.S. 2021. Genetic fingerprinting and aflatoxin production of Aspergillus section Flavi associated with groundnut in eastern Ethiopia. BMC Microbiology. 21:239. https://doi.org/10.1186/s12866-021-02290-3.
Patel, J.D., Wang, M.L., Dang, P.M., Butts, C.L., Lamb, M.C., Chen, C.Y. 2022. Insights into the genomic architecture of seed and pod quality traits in the U.S. peanut mini-core diversity panel. Plants. 11(7):837. https://doi.org/10.3390/plants11070837.
Sobolev, V., Walk, T., Arias De Ares, R.S., Massa, A.N., Orner, V.A., Lamb, M.C. 2022. Transformation of major peanut (arachis hypogaea) stilbenoid phytoalexins caused by selected microorganisms. Journal of Agricultural and Food Chemistry. 70,1101-1110. https://doi.org/10.1021/acs.jafc.1c06122.
Jimenez-Rojas, M., Andueza Noh, R.H., Noh-Ake, O.I., Potter, D., Ortiz-Garcia, M.M., Arias De Ares, R.S., Martinez-Castillo, J. 2021. Genetic diversity of Huaya India (Melicoccus o1iviformis Kunth), a neglected Neotropical fruit crop. Scientia Horticulturae. 290:110535. https://doi.org/10.1016/j.scienta.2021.110535.
