Location: National Peanut Research Laboratory
2022 Annual Report
Objectives
1. Evaluate pathogen-host interactions, including enzyme production by host and pathogen during aflatoxin accumulation, and identify potential resistance genes for aflatoxin control.
2. Mine the diploid Arachis germplasm collections in peanut to identify resistance to various pathogens, characterize novel sources of resistance to important fungal pathogens, and introgress genes into cultivated peanuts.
2a. Screen wild peanut germplasm collection to identify useful germplsm for resistance to important fungal pathogens (e.g. Aspergillus, Cercospora, Cercosporidium, and Sclerotinia spp.).
2b. Transfer economically important genetic traits from wild Arachis species to cultivated peanuts.
3. Develop integrated strategies for management of fungus-associated peanut diseases.
Approach
Mycotoxins are toxic secondary fungal metabolites. Contamination of crops with mycotoxins, particularly aflatoxins, is an important food safety issue and threatens the competitiveness of United States agriculture in the world market. Aflatoxins are strong carcinogens produced in crops by the fungus Aspergillus (A.) flavus. Contamination of crops with aflatoxins is an important food safety issue. The purpose of this project is to develop effective integrated strategies for controlling mycotoxin accumulation and fungal diseases that cause yield losses in peanut. One strategy for reducing aflatoxins is to prevent Aspergillus from invading crops. To achieve this goal, the first objective will evaluate fungus-plant interactions, gene expression and chemical profiling of host and pathogen during aflatoxin accumulation. Another strategy for aflatoxin reduction is to prevent its formation by the fungus. This strategy is based on data from our recent research showing that selected peanut stilbenoids significantly reduce or completely block aflatoxin biosynthesis in A. flavus. The second objective will explore wild Arachis germplasm collections to identify resistance to A. flavus, determine and characterize novel sources of resistance to important fungal pathogens, including species causing early and late leaf spot and white mold diseases, and introgress genes into cultivated peanuts. New genetic and genomic resources will be developed to identify mechanisms of pre-harvest aflatoxin resistance in selected wild peanut germplasm. Understanding these mechanisms is fundamental to efficiently introgress favorable alleles from wild Arachis species to reduce aflatoxin in elite peanut cultivars. The third objective, which is related to the first and second objectives, is to combine knowledge and methodology obtained from these objectives on the reduction of aflatoxin in peanut. The ultimate goal of this objective is to establish new peanut germplasm with increased resistance to toxigenic A. flavus.
Progress Report
Significant progress was made towards Objective 1. The second-year study of phytoalexin detoxification by important fungal genotypes was completed, and the results were published in a peer-reviewed journal. The second-year aflatoxin suppression experiments with special reference to chemical and genetic data in collaboration with a scientist from Dawson, Georgia, were conducted, and the results were submitted to a peer-reviewed journal. To accomplish Objectives 2 and 3, prospective peanut genotypes with resistance to early and late spot diseases and to aflatoxin accumulation were incorporated into the pre-breeding pipeline developed at National Peanut Research Laboratory (NPRL). This includes the development of novel interspecific F1 hybrids between A-genome and B-genome wild diploid species, followed by whole-genome duplication; transcriptome variants discovery; and single nucleotide polymorphisms (SNP) marker development. A polymerase chain reaction (PCR) allelic discrimination platform called rhAmp SNP genotyping used to validate SNPs markers in genotypes with contrasting aflatoxin accumulation. High-confidence SNPs were selected and validated from loci showing polymorphism in at least one pairwise comparison. In collaboration with other USDA-ARS scientists at Frederick, Maryland, the project identified ribonucleic acid sequences of mosaic virus, peanut mottle virus, and tomato spotted wilt virus, all three viruses co-existing in individual plants. Research progress is being presented at the Plant Health 2022 conference (Pittsburgh, PA). The NPRL research team, in collaboration with other peanut researchers identified genome regions conferring resistance Sclerotinia blight disease using a recombined inbred line (RIL) population with introgressed genes from three wild diploid species, Arachis cardenasii, Arachis correntina, and Arachis batizocoi. Two consistent quantitative trait loci were detected in two different chromosomes. A manuscript was submitted to a peer reviewed journal.
Accomplishments
1. Generation of genetic and genomic resources for the introgression of desirable traits from wild diploid species into cultivated peanut. The development of genetic resources through interspecific hybridization, followed by whole genome duplication is fundamental for the transfer of beneficial alleles between otherwise reproductively isolated species. While the generation of genomic resources, including transcriptome based single nucleotide polymorphisms (SNPs) and small insertion and/or deletion polymorphisms (InDels) is critical for a rapid and effective development of enhanced germplasm through marker-assisted introgression. ARS scientists at Dawson, Georgia, generated interspecific F1 hybrids (first filial generation seeds) between wild diploid species, followed by whole-genome duplication. The project further revealed extensive diversity in the peanut transcriptome in terms of SNPs, InDels, and gene expression patterns. The overall study identified, annotated, and validated novel genetic variants associated with peanut transcriptional responses to infection caused by the soil fungus Aspergillus flavus and corresponding accumulation of carcinogenic aflatoxin. These findings provide new genomic resources for the selection of SNP/InDel variants that will be used to develop markers for peanut improvement, and a potential source for next generation breeding. Research results contributed to the Peanut Genome Initiative – Phase II document.
2. Transformation of Mmjor peanut phytoalexins caused by selected microorganisms. The peanut plant accumulates defensive phytoalexins in response to the presence of soil fungi, which in turn produce phytoalexin-detoxifying enzymes for successfully invading the plant host. The goal of the present research was to systematically study the dynamics of major peanut phytoalexin transformation (change of chemical structure)/detoxification by 18 important fungal and bacterial species; this goal was accomplished in feeding experiments that comprised a total of 1728 individual growing cells. Data were obtained through the use of a multi-platform approach, including ultra-performance liquid chromatography, mass spectrometry. Present research quantitatively revealed the concomitant degradation of the major peanut phytoalexin, arachidin-3, by Aspergillus species into its derivatives, arachidin-1 and/or SB-1, as well as similar degradation of arachidin-1 into SB-1. The observed transformations are attributed to the phytoalexins detoxification. Aspergillus niger as well as other fungal and bacterial species tested, were incapable of changing the structure of arachidin-3 in contrast to Aspergillus species that are known to invade preharvest peanut seeds. The research provided new knowledge on the dynamics of peanut phytoalexins transformations by essential fungi. These findings will contribute to the elucidation of detoxification mechanisms employed by fungi to compromise the plant’s defense system and could lead to new strategies for preventing plant invasion by the fungi that produce aflatoxins. The results were published in a peer-reviewed journal.
Review Publications
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.
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.
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.
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.
Park, J., Massa, A.N., Douches, D., Coombs, J., Akdemir, D., Yencho, G.C., Whitworth, J.L., Novy, R.G. 2021. Linkage and QTL mapping for tuber shape and specific gravity in a tetraploid mapping population of potato representing the russet market class. Biomed Central (BMC) Plant Biology. 21. Article 507. https://doi.org/10.1186/s12870-021-03265-2.
