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Like many other crops, the cultivated peanut (Arachis hypogaea L.) is of hybrid origin and has a polyploid genome that contains essentially complete sets of chromosomes from two ancestral species. Here we report the genome sequence of peanut and show that after its polyploid origin, the genome has evolved through mobile-element activity, deletions and by the flow of genetic information between corresponding ancestral chromosomes (that is, homeologous recombination). Uniformity of patterns of homeologous recombination at the ends of chromosomes favors a single origin for cultivated peanut and its wild counterpart A. monticola. However, through much of the genome, homeologous recombination has created diversity. Using new polyploid hybrids made from the ancestral species, we show how this can generate phenotypic changes such as spontaneous changes in the color of the flowers. We suggest that diversity generated by these genetic mechanisms helped to favor the domestication of the polyploid A. hypogaea over other diploid Arachis species cultivated by humans.

Single nucleotide polymorphic markers (SNPs) are attractive for use in genetic mapping and marker-assisted breeding because they can be scored in parallel assays at favorable costs. However, scoring SNP markers in polyploid plants like the peanut is problematic because of interfering signal generated from the DNA bases that are homeologous to those being assayed. The present study used a previously constructed 1536 GoldenGate SNP assay developed using SNPs identified between two A. duranensis accessions. In this study, the performance of this assay was tested on two RIL mapping populations, one diploid (A. duranensis × A. stenosperma) and one tetraploid [A. hypogaea cv. Runner IAC 886 × synthetic tetraploid (A. ipaënsis × A. duranensis)(4×)]. The scoring was performed using the software GenomeStudio version 2011.1. For the diploid, polymorphic markers provided excellent genotyping scores with default software parameters. In the tetraploid, as expected, most of the polymorphic markers provided signal intensity plots that were distorted compared to diploid patterns and that were incorrectly scored using default parameters. However, these scorings were easily corrected using the GenomeStudio software. The degree of distortion was highly variable. Of the polymorphic markers, approximately 10% showed no distortion at all behaving as expected for single-dose markers, and another 30% showed low distortion and could be considered high-quality. The genotyped markers were incorporated into diploid and tetraploid genetic maps of Arachis and, in the latter case, were located almost entirely on A genome linkage groups.

Abstract Background Cultivated peanut (Arachis hypogaea) is an allotetraploid species whose ancestral genomes are most likely derived from the A-genome species, A. duranensis, and the B-genome species, A. ipaensis. The very recent (several millennia) evolutionary origin of A. hypogaea has imposed a bottleneck for allelic and phenotypic diversity within the cultigen. However, wild diploid relatives are a rich source of alleles that could be used for crop improvement and their simpler genomes can be more easily analyzed while providing insight into the structure of the allotetraploid peanut genome. The objective of this research was to establish a high-density genetic map of the diploid species A. duranensis based on de novo generated EST databases. Arachis duranensis was chosen for mapping because it is the A-genome progenitor of cultivated peanut and also in order to circumvent the confounding effects of gene duplication associated with allopolyploidy in A. hypogaea. Results More than one million expressed sequence tag (EST) sequences generated from normalized cDNA libraries of A. duranensis were assembled into 81,116 unique transcripts. Mining this dataset, 1236 EST-SNP markers were developed between two A. duranensis accessions, PI 475887 and Grif 15036. An additional 300 SNP markers also were developed from genomic sequences representing conserved legume orthologs. Of the 1536 SNP markers, 1054 were placed on a genetic map. In addition, 598 EST-SSR markers identified in A. hypogaea assemblies were included in the map along with 37 disease resistance gene candidate (RGC) and 35 other previously published markers. In total, 1724 markers spanning 1081.3 cM over 10 linkage groups were mapped. Gene sequences that provided mapped markers were annotated using similarity searches in three different databases, and gene ontology descriptions were determined using the Medicago Gene Atlas and TAIR databases. Synteny analysis between A. duranensis, Medicago and Glycine revealed significant stretches of conserved gene clusters spread across the peanut genome. A higher level of colinearity was detected between A. duranensis and Glycine than with Medicago. Conclusions The first high-density, gene-based linkage map for A. duranensis was generated that can serve as a reference map for both wild and cultivated Arachis species. The markers developed here are valuable resources for the peanut, and more broadly, to the legume research community. The A-genome map will have utility for fine mapping in other peanut species and has already had application for mapping a nematode resistance gene that was introgressed into A. hypogaea from A. cardenasii.

'TifNV‐HG' (Reg. no. CV‐153, PI 702637) is a runner‐type peanut (Arachis hypogaea L. subsp. hypogaea var. hypogaea) cultivar released by the USDA‐ARS and the Georgia Agricultural Experiment Station in 2021. TifNV‐HG was developed at the University of Georgia Coastal Plain Experiment Station, Tifton, GA. TifNV‐HG is a high oleic acid, runner market‐type cultivar that also has resistance to the peanut root‐knot nematode [Meloidogyne arenaria (Neal) Chitwood race 1] and resistance to spotted wilt caused by Tomato spotted wilt tospovirus (TSWV). Breeding populations were developed by hybridizing C1805‐617‐2 × 'Georgia‐06G'. C1805‐617‐2 is a breeding line selected from the cross of 'Tifguard' × 'Florida‐07'. Marker‐assisted selection was used in the development of TifNV‐HG to select for nematode resistance and the high oleic to linoleic (O/L) characteristic. TifNV‐HG has a high level of resistance to both the peanut root‐knot nematode and TSWV and has a high ratio of oleic acid to linoleic acid. When tested in fields without nematode pressure, TifNV‐HG exhibited yields that were at least similar to other currently grown peanut cultivars. When tested in fields with nematode pressure, TifNV‐HG exhibited yield that was at least equivalent to the nematode‐resistant cultivars TifNV‐High O/L and Georgia‐14N and significantly higher than the susceptible check cultivar Georgia‐06G. TifNV‐HG exhibited higher grade in comparison to TifNV‐High O/L. Core Ideas: TifNV‐HG is a new runner‐type peanut cultivar.TifNV‐HG has resistance to the peanut root‐knot nematode and Tomato spotted wilt virus.TifNV‐HG has a high oleic fatty acid ratio.TifNV‐HG has high grade potential than the previous cultivar TifNV‐High O/L. [ABSTRACT FROM AUTHOR]

Drought stress is one of the major environmental factors limiting peanut (Arachis hypogea L.) productivity. Peanut response to drought varies depending on genotypic characteristics, crop growth stages, and environmental conditions. The objective of this study was to evaluate the effects of drought stress and rehydration on symbiotic nitrogen fixation and carbon isotope discrimination in peanut genotypes with varying drought tolerance. Experiments were conducted for 2 years in rainout shelters under three irrigation regimes: irrigated control, middle‐season drought with rehydration, and late‐season drought with rehydration. Reduction in percentages of shoot N derived from the atmosphere (%Ndfa) occurred under both drought treatments in both years; a greater reduction occurred under middle‐season drought than under late‐season drought. Middle‐season drought negatively affected carbon isotope discrimination in both years, although there were no significant differences under late‐season drought. Variabilities in %Ndfa and carbon isotope discrimination were found among different genotypes. Under middle‐season drought, both %Ndfa and carbon isotope discrimination were higher in drought‐tolerant lines than drought‐susceptible lines. The most drought‐tolerant lines had the highest N‐fixing capacity under both drought treatments. Additionally, there was a positive correlation between %Ndfa and carbon isotope discrimination under both drought treatments. In most genotypes, %Ndfa remained unchanged after rehydration; only a few genotypes showed a slight increase in %Ndfa after rehydration following both drought treatments. Our data suggested that symbiotic nitrogen fixation in many peanut genotypes was negatively affected by drought and may not recover from the damage caused by drought upon rehydration. [ABSTRACT FROM AUTHOR]