Location: Crop Genetics and Breeding Research2021 Annual Report
Objective 1: Identify and characterize genes/Quantitative Trait Locus (QTLs) controlling resistance to major diseases (leaf spot, white mold, rhizoctonia limb rot, and nematodes) and drought stress, and use the information in marker-assisted breeding to develop improved high oleic (oleic/linoleic fatty acid ratio) peanut cultivars or germplasm with tolerance to biotic and abiotic stresses. Sub-objective 1.A.: Conduct phenotypic evaluations of recombinant inbred line (RIL) populations to aid in the identification and characterization of genes/QTLs controlling resistance/tolerance to biotic and abiotic stresses. Sub-objective 1.B.: Develop improved high oleic peanut cultivars or germplasm with resistance to nematodes and improved resistance to leaf spot. Sub-objective 1.C.: Develop high oleic peanut germplasm with improved drought tolerance and reduced preharvest aflatoxin contamination (PAC).
1.A. Sixteen structured recombinant inbred line (RIL) populations were developed using parents that were selected to maximize genetic diversity while meeting practical breeding objectives. In-depth phenotyping and genotyping of the populations will be conducted to identify genetic markers that can be used in peanut cultivar development. 1.B. Breeding populations will be developed by hybridizing cultivars with high oleic acid with high yielding breeding lines with resistance to the peanut root-knot nematode and/or resistance to leaf spot. Marker assisted selection will be utilized to select early generation progeny that are homozygous for the desired characteristics (high oleic, nematode resistance, and/or leaf spot resistance). Selections in later generations will focus on field resistance to tomato spotted wilt virus, high yield, and other agronomic characteristics. 1.C. Breeding populations will be developed by hybridizing high-yielding, high-oleic cultivars with sources of resistance to preharvest aflatoxin contamination and sources of resistance to drought. These populations will be evaluated under field conditions with drought and heat stress imposed by covering the entire test area with a mobile greenhouse. Aflatoxin contamination of the subsequent yield will be determined using the immunoaffinity column fluorometer method. Progeny will be selected based on relatively low aflatoxin and/or relatively high pod yields.
Crosses were made by ARS scientists at Tifton, Georgia, to combine resistance to biotic and abiotic stresses with high yield, good grade, and high oleic fatty acid content. Populations were advanced to a more inbred state when marker assisted selection (MAS) was used by ARS scientists to identify individuals that will breed true for high oleic fatty acid content and/or nematode resistance and/or leaf spot resistance. Progeny from these individuals were then evaluated for resistance to other biotic and/or abiotic stresses, yield, and other agronomic characteristics. One recombinant inbred line (RIL) population (Florida-07 x C76-16) was phenotyped for resistance to drought using a replicated field study. Quantitative trait loci (QTLs) for drought tolerance were identified.
1. Identify genomic regions that provide high resistance to late leaf spot (LLS) in peanut. ARS scientists at Tifton, Georgia, believe LLS disease is one of the costliest diseases of United States grown peanut. IAC 322 is a breeding line that contains three introgressed chromosome segments from a wild species that provides a very high level of resistance to LLS. Genetic markers are available for these genomic regions, so marker assisted selection (MAS) to combine resistance with acceptable agronomic performance is feasible. An ARS researcher in Tifton, Georgia conducted a study to identify the genomic regions or combination of genomic regions that provide the highest level of resistance. A segregating population was developed and individuals with single introgressions, individuals with all pairwise combinations, and individuals with all three introgressions were identified. Field evaluation of this material indicated that major genes for resistance are contained on the introgressions from the bottom of chromosome A03 and the top of chromosome A02. The third introgression did not add significantly to the levels of resistance to LLS. These results will allow breeders to use MAS to develop peanut varieties with resistance to LLS more effectively and efficiently.
2. Development and release of germplasm and associated genetic markers for resistant to leaf spot in peanut. ARS scientists at Tifton, Georgia,believe Late leaf spot disease (LLS) is one of the more serious peanut diseases due to its widespread occurrence across the world and the high percentage of yield reduction in susceptible cultivars. Host resistance to LLS is much needed to reduce management costs of fungicide sprays and improve the sustainability and profitability of peanut farmers. An ARS researcher in Tifton, Georgia, developed a breeding population that was segregating for leaf spot resistance and two lines with very high levels of resistance were selected for release. The resistance is due to introgressed genes from a wild diploid relative of peanut. Genetic markers can be used to determine the presence or absence of each introgressed segment which will allow breeders to use marker assisted selection. Releasing leaf spot resistant germplasm packaged with breeder friendly genetic markers should accelerate peanut breeding progress.
3. Resistance to fall armyworm (FAW) in peanut. ARS scientists at Tifton, Georgia, suggest FAW is a major defoliating pest in the Americas and has recently become an economically devastating, invasive pest in Sub-Saharan Africa, as well as in Asia. Genetic sources with strong FAW resistance are limited in cultivated peanut due to its narrow genetic base. On the other hand, wild peanut relatives have diverse resistances against a wide range of peanut pests and diseases. An ARS researcher guided a graduate student who identified FAW resistance in newly created allotetraploids (crosses of cultivated peanut with wild relatives). Resistant allotetraploid lines identified in this study by ARS scientists can be used in breeding programs in the United States and shared with breeding programs in East and West Africa to introgress FAW resistance into elite varieties.
4. Identification of genetic markers for resistance to stem rot. ARS scientists at Tifton, Georgia, believe Marker Assisted Selection (MAS) can be used to improve the efficiency and effectiveness of developing new peanut varieties. Genetic marker linked to important traits are needed before MAS can be implemented. Stem rot is one of the most damaging disease of peanut with regards to both cost of control and yield loss. An ARS researcher in Tifton, Georgia genotyped and phenotyped a population that was segregating for resistance to stem rot to identify two genetic markers linked to resistance. These markers were then validated by ARS scientists in a blind selection test by selecting only with markers in a part of the population not used for initial analysis. These genetic markers will allow breeders to use MAS to more effectively and efficiently develop peanut varieties with resistance to stem rot.
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Wang, X., Yang, X., Feng, Y., Dang, P.M., Wang, W., Graze, R., Clevenger, J., Chu, Y., Ozias-Akins, P., Holbrook Jr, C.C., Chen, C. 2021. Transcriptome profile reveals drought induced genes preferentially expressed in response to water deficit in cultivated peanut (Arachis hypogaea L.). Frontiers in Plant Science. 12:645291. https://doi.org/10.3389/fpls.2021.645291.
Cui, R., Clevenger, J., Chu, Y., Brenneman, T., Isleib, T.G., Holbrook Jr, C.C., Ozias-Akins, P. 2020. Quantitative trait loci sequencing-derived molecular markers for selection of stem rot resistance in peanut. Crop Science. 60:2008-2018. https://doi.org/10.1002/csc2.20047.
Gimode, D., Chu, Y., Dean, L.L., Holbrook Jr, C.C., Fonceka, D., Ozias-Akins, P. 2020. Seed composition survey of a peanut CSSL population reveals introgression lines with elevated oleic/linoleic profile. Peanut Science. 47:139–149. https://doi.org/10.3146/PS20-17.1.
Levinson, C.M., Marasigan, K.M., Chu, Y., Stalker, T.H., Holbrook Jr, C.C., Ni, X., Williams, W.P., Ozias-Akins, P. 2020. Resistance to fall armyworm (Lepidoptera: Noctuidae) feeding was identified in nascent allotetraploids cross-compatible to cultivated peanut (Arachis hypogaea). Peanut Science. 47:123-134. https://doi.org/10.3146/PS20-13.1.