Location: National Peanut Research Laboratory
2019 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. 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
Substantial progress was made toward a better understanding of the role of stilbenoid phytoalexins in fungus-peanut seed interaction and the suppression of aflatoxin formation. The first stage of the study was completed, and the results were published in a scientific peer-reviewed journal. Research progress was also reported at the 51th Annual Meeting of the American Peanut Research and Education Society, Auburn, Alabama, July 9-11, 2019. Significant progress was made toward Sub-objectives 2a and 2b. Prospective peanut accessions (selected during 2017 and 2018) entered the research pipeline developed at the Laboratory in Dawson, Georgia, and consisting of seed increase, field evaluation under controlled environmental conditions, high-throughput genotyping, transcriptome analysis, trait introgression, and marker development. Transcriptome sequence and analysis of Aspergillus-challenged seeds was completed for an initial set of ten aflatoxin resistant and susceptible peanut genotypes. Combined with genome-wide SNP genotyping data, aflatoxin formation, and phytoalexin response, this information is being utilized to advance ongoing genetic studies, trait introgression, and marker development. Pre-breeding toward trait introgression was initiated using the resistant candidates. Research progress were presented at the 10th Advances in Arachis through Genomics and Biotechnology (AAGB) Conference, Saly, Senegal, Nov 12-18, 2018 and the 51th Annual Meeting of the American Peanut Research and Education Society, Auburn, Alabama, July 9-11, 2019. In a continued effort to identify germplasm with resistance to important peanut pathogens, scientists at Dawson, Georgia, genotyped 350 accessions of wild Arachis species from the U.S. peanut germplasm collection. The research implemented a new genotyping technology based on the RNase H2-dependent polymerase chain reaction to verify the genetic identity of a source of resistance to peanut smut (Thecaphora frezzi). The study was completed and a manuscript submitted to a peer reviewed Journal is under review.
Accomplishments
1. Inhibition of aflatoxin formation in Aspergillus species by peanut stilbenoids in the course of peanut-fungus interaction. Common soil fungi, A. flavus and A. parasiticus, are opportunistic pathogens that invade preharvest peanut seeds. These fungi often produce carcinogenic aflatoxins that pose a threat to human and animal health. Under favorable conditions, the fungus-challenged peanut seeds produce phytoalexins, structurally related stilbenoids, capable of retarding fungal development. ARS researcher in Dawson, Georgia, revealed for the first time that in the course of peanut-fungus interaction, aflatoxin formation was completely suppressed by peanut phytoalexins in A. flavus and A. parasiticus strains tested, when low concentrations of spores were introduced to wounded peanut seeds. In most of the experiments, when fungal spore concentrations were 2 orders of magnitude higher, the spores germinated and produced aflatoxins. Of all experimental seeds that showed fungal growth, 57.7% were aflatoxin-free, compared to the control (0%), after 72 h of incubation. The research provided new knowledge on the aflatoxin/phytoalexin formation in the course of peanut-fungus interaction.
2. Identification, characterization, and introgression of new genetic sources with resistance to peanut pathogens. The genetics of resistance to aflatoxin accumulation in peanut seeds is complex. The lack of an effective phenotyping method has hindered the development of resistant cultivars or alternative methods of control. ARS researchers in Dawson, Georgia, have developed a new method to screen for aflatoxin resistance in the laboratory. To date, the method has allowed the identification of aflatoxin-resistance in wild peanut germplasm. a) A dual transcriptome sequence of Aspergillus-challenged seeds enabled the simultaneous analysis of seed and pathogen specific transcripts. The study uncovered gene expression differences in the peanut/fungus interaction between susceptible and aflatoxin resistance germplasms. Results from this study provided unique insights into defense strategies used by peanut seeds against Aspergillus infection and aflatoxin accumulation. b) In addition, ARS researchers in Dawson, Georgia, in collaboration with other peanut researchers, published the first two reports on peanut smut genetic resistance. The studies identified smut resistance in both wild Arachis species and peanut landraces, and further demonstrated its introgression into elite peanut cultivars. These findings are expected to have a significant impact on peanut breeding programs worldwide.
Review Publications
Bressano, M., Massa, A.N., Arias De Ares, R.S., Oddino, C., De Blas, F., Faustinelli, P.C., Soave, S., Soave, J., Perez, M., Sobolev, V., Balzarini, M., Buteler, M.I., Seijo, G.J. 2019. Introgression of peanut smut resistance from landraces to elite peanut cultivars (Arachis hypogaea L.). PLoS One. https://doi.org/10.1371/journal.pone.0211920.
Massa, A.N., Manrique-Carpintero, N.C., Coombs, J.J., Haynes, K.G., Bethke, P.C., Yencho, C.G., Brandt, T., Gupta, S.K., Novy, R.G., Douches, D.S. 2018. Linkage analysis and QTL mapping in a tetraploid russet mapping population of potato. BioMed Central (BMC) Genetics. 19:87. https://doi.org/10.1186/s12863-018-0672-1.
De Blas, F., Bressano, M., Teich, I., Balzarini, M., Arias De Ares, R.S., Manifesto, M., Costero, B., Oddino, C., Soave, S., Soave, J., Buteler, M., Massa, A.N., Seijo, G. 2019. Identification of smut resistance in wild Arachis species and its introgression into peanut elite lines. Crop Science. https://www.doi.org/10.2135/cropsci2018.10.0656.
Pilon, C., Snider, J.L., Sobolev, V., Chastain, D.R., Sorensen, R.B., Meeks, C.D., Massa, A.N., Walk, T., Singh, B. 2018. Assessing stomatal and non-stomatal limitations to carbon assimilation under progressive drought in peanut (Arachis hypogaea L.). Plant Physiology Journal. 231:124-134. https://doi.org/10.1016/j.jplph.2018.09.007.
Sobolev, V., Walk, T., Arias De Ares, R.S., Massa, A.N., Lamb, M.C. 2019. Inhibition of aflatoxin formation in aspergillus species by peanut (Arachis hypogaea) seed stilbenoids in the course of peanut-fungus interaction. Journal of Agricultural and Food Chemistry. 67(22):6212-6221. https://doi.org/10.1021/acs.jafc.9b01969.
