Location: National Peanut Research Laboratory
2024 Annual Report
Objectives
Objective 1
Identify and integrate beneficial genes from disease-resistant peanut and wild peanut sources into genetically stable peanut germplasm.
Sub-objective 1A.
Screening for aflatoxin accumulation under laboratory conditions.
Sub-objective 1B.
Identification of disease resistance-associated genes and plant defense mechanisms.
Sub-objective 1C.
Integration of beneficial alleles from wild diploid Arachis species into genetically stable peanut germplasm.
Objective 2
Define specific defensive roles of peanut phytoalexins against Aspergillus spp. and other fungal pathogens and identify their genetic sources as potential resistance to fungal diseases and aflatoxin contamination.
Sub-objective 2A.
Determination of phytoalexin profiles in experimental and field seeds and search for new phytoalexins.
Sub-objective 2B.
Study of potential involvement of pegs in contamination of peanut seeds with aflatoxins.
Approach
Peanut (Arachis hypogaea) is one of the major food crops in the world. Most of the pathogens that attack peanuts are of fungal origin and are evident etiological factors of over 40 economically important peanut diseases. Aspergillus flavus and A. parasiticus are opportunistic fungal parasites that often invade peanut seeds and produce carcinogenic aflatoxins. Contamination of peanuts with aflatoxins is an important food safety issue and threatens the competitiveness of the United States agriculture in the world market. Aflatoxin monitoring and reprocessing of contaminated peanuts is a passive and costly practice to prevent aflatoxins from entering the food chain. Current peanut cultivars often demonstrate limited resistance to fungal pathogens. Therefore, wild peanut species have received substantial consideration as sources of disease resistance because the narrow genetic base of cultivated peanuts cannot provide the necessary levels of resistance to defend the peanut plant. A prospective approach to reduce disease pressure and aflatoxin contamination is to develop resistant peanut cultivars through introgression of beneficial genes and alleles from wild peanut species into elite cultivars. To achieve this goal, the first objective to identify and integrate beneficial genes from disease-resistant peanut and wild peanut sources into genetically stable peanut germplasm will use this approach. In conjunction with this objective, another promising strategy/second objective is to define specific defensive roles of peanut phytoalexins against Aspergillus spp. and other fungal pathogens and identify their genetic sources as potential resistance to fungal diseases and aflatoxin contamination. Both approaches will generate new knowledge on the mechanisms of peanut resistance to fungal invasion and a faster release of enhanced germplasm and cultivars. The ultimate goal of this project is to reduce peanut disease load and to develop improved germplasm. The beneficiaries of the successful accomplishment of the project goal are breeders and all segments of the peanut industry.
Progress Report
ARS researchers at Dawson, Georgia made significant advancement towards achieving Objective 1. Favorable genes for increased resistance to aflatoxin accumulation and late leaf spot disease in peanuts were integrated into synthetic allotetraploids. This newly developed germplasm was generated by interspecific hybrids between wild diploid peanut species, followed by colchicine treatment to induce whole genome duplication. The interspecific hybrids were confirmed using molecular markers, while the amphidiploids were validated by flow cytometry and array-based single nucleotide polymorphism genotyping. In addition, a total of 400 breeding lines were planted for generation advancement of two mapping populations segregating for resistance to important peanut pathogens including Aspergillus flavus, tomato spotted wilt virus, mosaic virus, and peanut mottle virus. The project contributed new knowledge to a population of 33 accessions of Arachis duranensis from the USDA peanut germplasm collection, which consisted of characterization of genetic diversity and population structure, resistance to leaf spot diseases, and genotype-environment associations. Results from this study were published in a peer-reviewed journal. The project also contributed to the publication of a draft genome of Nothopassalora personata, which is the causal agent of late leaf spot, an important foliar disease in peanuts.
Substantial progress has been made to achieve Objective 2A. Full High Performance Liquid Chromatographic profiles of fungal-challenged and intact seed extracts from available resistant and susceptible accessions of diploid and tetraploid peanut genotypes were obtained. The data were analyzed in terms of correlation of aflatoxin-phytoalexin ratios with the genetic and genomic information. The results of this research allowed to better understand the plant-fungus interactions and to attempt reliable prediction of a peanut genotype resistance to aflatoxin accumulation using the quantitative phytoalexin profiles.
In order to promote basic and applied science among university students and to make ARS/NPRL activity visible, two NPRL scientists took part in all meetings of the 5-member advisory board of the Broadening Participation in STEM Grant from the National Science Foundation hosted by Albany State University, Albany, GA. Eight undergraduate STEM students received 2 days of training, and 4 students received 14-day full time training at NPRL on application of STEM in research, including chemistry, applied mathematics, biology, microscopy, DNA analysis, use of scientific instruments and software.
The same scientists actively participated in all meetings of the 6-member advisory board of the Robert Noyce Teacher Scholarship Program grant from the National Science Foundation obtained by Albany State University, Albany, Georgia. Both USDA scientists provided hands-on training to 5 teachers of STEM program, recipients of the Noyce scholarship.
Accomplishments
1. Developing novel genetic resources for peanut improvement. An improved single-seed analysis method for aflatoxin and phytoalexin-assisted selection of resistant peanut genotypes was developed by the NPRL scientists for the screening hundreds of samples. The method is sensitive, accurate, and requires smaller quantities of reagents, making the entire analytical procedure more affordable. The method was published in the Journal of Visualized Experiments. Novel genetic resources are needed to facilitate the transfer of desirable traits from wild diploid peanut species into cultivated peanut. NPRL scientists developed interspecific hybrids between two wild diploid species followed by chromosome doubling. These newly developed plant materials, also called synthetic allotetraploids, carry favorable genes for reduced aflatoxin accumulation and resistance to late leaf spot disease (LLS), thus facilitating the simultaneous introgression of resistance into cultivated peanut. It is anticipated that this enhanced germplasm will be incorporated into the nation-wide peanut breeding programs. NPRL scientists identified new sources of resistance to LLS in accessions of Arachis duranensis from the USDA germplasm peanut collection and reported in a scientific article published in the journal PLOs ONE. The industry loss due to the peanut LLS exceeds $40 M/year.¿The disease is caused by a fungal pathogen, Nothopassalora personata. In a joint effort, scientists at the NPRL identified and characterized four genetic variants of this fungus and determined that each morphotype has a different composition of secondary metabolites.¿We compared the chemical profiles with gene expression and interpreted the potential impact of these fungal variants on the peanut plant response. We made available all four N. personata isolates to the USDA-ARS-NRRL collection to assist other scientific groups with valuable information and materials for a better understanding of fungal-plant interactions; this understanding is crucial to achieve LLS resistance in peanut.
Review Publications
Monquillot, J.H., Arias De Ares, R.S., Orner, V.A., Massa, A.N., Sobolev, V., Bernardi-Lima, N., Paredes, J., Oddino, C., Carmona, M., Conforto, C. 2024. Draft genome sequence data of Nothopassalora personata, peanut foliar pathogen from Argentina. Data in Brief. 53:Article 110158. https://doi.org/10.1016/j.dib.2024.110158.
Massa, A.N., Sobolev, V., Faustinelli, P.C., Tallury, S.P., Stalker, T., Lamb, M.C., Arias De Ares, R.S. 2024. Genetic diversity, disease resistance, and environmental adaptation of arachis duranensis L.: new insights from landscape genomics. PLOS ONE. 19(4):Article e0299992. https://doi.org/10.1371/journal.pone.0299992.
Sobolev, V., Arias De Ares, R.S., Massa, A.N., Walk, T., Orner, V.A., Lamb, M.C. 2024. Non-destructive SPE-UPLC-based quantification of aflatoxins and stilbenoid phytoalexins in single peanut (arachis spp.) seeds. Journal of Visualized Experiments. (206). Article e65574. https://dx.doi.org/10.3791/66574.