[Show abstract][Hide abstract] ABSTRACT: Background
Peanut is one of the major source for human consumption worldwide and its seed contain approximately 50% oil. Improvement of oil content and quality traits (high oleic and low linoleic acid) in peanut could be accelerated by exploiting linked markers through molecular breeding. The objective of this study was to identify QTLs associated with oil content, and estimate relative contribution of FAD2 genes (ahFAD2A and ahFAD2B) to oil quality traits in two recombinant inbred line (RIL) populations.ResultsImproved genetic linkage maps were developed for S-population (SunOleic 97R × NC94022) with 206 (1780.6 cM) and T-population (Tifrunner × GT-C20) with 378 (2487.4 cM) marker loci. A total of 6 and 9 QTLs controlling oil content were identified in the S- and T-population, respectively. The contribution of each QTL towards oil content variation ranged from 3.07 to 10.23% in the S-population and from 3.93 to 14.07% in the T-population. The mapping positions for ahFAD2A (A sub-genome) and ahFAD2B (B sub-genome) genes were assigned on a09 and b09 linkage groups. The ahFAD2B gene (26.54%, 25.59% and 41.02% PVE) had higher phenotypic effect on oleic acid (C18:1), linoleic acid (C18:2), and oleic/linoleic acid ratio (O/L ratio) than ahFAD2A gene (8.08%, 6.86% and 3.78% PVE). The FAD2 genes had no effect on oil content. This study identified a total of 78 main-effect QTLs (M-QTLs) with up to 42.33% phenotypic variation (PVE) and 10 epistatic QTLs (E-QTLs) up to 3.31% PVE for oil content and quality traits.ConclusionsA total of 78 main-effect QTLs (M-QTLs) and 10 E-QTLs have been detected for oil content and oil quality traits. One major QTL (more than 10% PVE) was identified in both the populations for oil content with source alleles from NC94022 and GT-C20 parental genotypes. FAD2 genes showed high effect for oleic acid (C18:1), linoleic acid (C18:2), and O/L ratio while no effect on total oil content. The information on phenotypic effect of FAD2 genes for oleic acid, linoleic acid and O/L ratio, and oil content will be applied in breeding selection.
[Show abstract][Hide abstract] ABSTRACT: Average yields of peanut in the U.S. set an all time record of 4,695 kg ha-1 in 2012. This far exceeded the previous record yield of 3,837 kg ha-1 in 2008. Favorable weather conditions undoubtedly contributed to the record yields in 2012; however, these record yields would not have been achievable without numerous technological advances that have been made in peanut production. The cumulative effect of these technological advances caused U.S. yields to increase six fold from 739 kg ha-1 in 1909 to 4,695 kg ha-1 in 2012. If we disregard the record yields of 2012, the average gain from 1909 to 2011 was 29.9 kg ha-1 yr-1. These yield gains are due to improved cultivars, advances in agronomic practices, improvements in practices and chemistries for control of weed and diseases, and increased use of precision agriculture, particularly for the digging and harvesting of the crop.
International Annual Meeting American Society of Agronomy/ Crop Science Society of America/ Soil Science Society of America 2013; 11/2013
[Show abstract][Hide abstract] ABSTRACT: Drought is a major abiotic stress limiting crop productivity worldwide especially in rain-fed areas. Plant physiologists and crop breeders have aimed to better understand the mechanisms underlying drought resistance to increase the success in breeding for drought resistant crops. The objectives of this study were to (i) determine the effects of different soil water availability on stomatal behavior and water use efficiency (WUE) of diverse peanut genotypes and ii) to investigate associations between surrogate physiological traits for drought tolerance. Eleven peanut genotypes and three soil moisture levels (field capacity, 2/3 available water and 1/3 available water) were assigned in a split plot design with four replications for two experiments. WUE, stomatal traits and root distribution (indicated by root length density, RLD, in the soil layers at 0-40 cm and 40-100 cm depths) were measured at 37, 67 and 97 days after sowing (DAS). Drought reduced stomatal aperture and stomatal conductance but increased WUE. Differential responses among peanut genotypes were observed for WUE, and stomatal conductance. ICGV 98300 and Tifton 8 had high stomatal conductance and WUE under moderate water stress. Stomatal conductance and %RLD (40-100cm) play an important roles in increasing WUE under mild drought stress.
[Show abstract][Hide abstract] ABSTRACT: Peanut seeds contain high amounts of oil and protein as well as some useful bioactive phytochemicals which can contribute to human health. The U.S. peanut mini-core collection is an important genetic resource for improving seed quality and developing new cultivars. Variability of seed chemical composition within the mini-core was evaluated from freshly harvested seeds for two years. Oil, fatty acid composition, and flavonoid/ resveratrol content were quantified by NMR, GC, and HPLC, respectively. Significant variability was detected in seed chemical composition among accessions and botanical varieties. Accessions were further genotyped with a functional SNP marker from the FAD2A gene using real-time PCR and classified into three genotypes with significantly different O/L ratios: wild type (G/G with a low O/L ratio <1.7), heterozygote (G/A with O/L ratio >1.4 but <1.7), and mutant (A/A with a high O/L ratio >1.7). The results from real-time PCR genotyping and GC fatty acid analysis were consistent. Accessions with high amounts of oil, quercetin, high seed weight, and O/L ratio were identified. The results from this study may be useful not only for peanut breeders, food processors, and product consumers to select suitable accessions or cultivars, but also for curators to potentially expand the mini-core collection.
Journal of Agricultural and Food Chemistry 02/2013; · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Peanut kernels are susceptible to colonization by some species of Aspergillus which, under conditions of drought and high temperatures, can produce aflatoxins prior to harvest. The objective of this research was to determine the mechanism by which the peanut root-knot nematode (Meloidogyne arenaria) increases aflatoxin contamination in peanut. Research determined 1) the role of nematode infection of roots vs. pods in increased aflatoxin contamination and 2) whether increased aflatoxin production in nematode-infected peanut is due to a greater percentage of small or immature kernels. An additional objective was to determine whether a peanut cultivar with resistance to M. arenaria would reduce the risk of preharvest aflatoxin contamination. In the greenhouse, researchers physically separated root growth from pod set and inoculated each location with M. arenaria or a water control in a 2 × 2 factorial design with 12–15 replications. Of the six trials conducted, data indicated that pod and root infection by M. arenaria was associated with elevated aflatoxin concentrations in one and three trials, respectively. This suggests that root infection by the nematode can increase aflatoxin concentrations in the peanut kernel. Another 2 × 2 factorial experiment was conducted with two peanut genotypes (Tifguard and TifGP-2) and two nematode treatments (with and without M. arenaria) with six replications. The cultivar Tifguard is resistant to M. arenaria and TifGP-2 is susceptible. The experiment was carried out in 24 field microplots equipped with a rainout shelter. The experiment was conducted five times from 2006 to 2010. Infection of TifGP-2 by M. arenaria did not lead to greater percentages of small kernels. In only one year (2007), nematodes appeared to increase the percentage of damaged kernels, though aflatoxin concentrations were not affected by nematodes in that year. In the rainout shelter experiment, 2006 was the only year where nematode infection of peanut increased aflatoxin concentrations. In that year, there were lower aflatoxin concentrations in the nematode-resistant cultivar Tifguard than the susceptible germplasm TifGP-2 (12 vs. 136 ng/g).
[Show abstract][Hide abstract] ABSTRACT: Drought affects yield of peanut, but its effect on oleic and linoleic acids that influence its oil quality of peanut genotypes with different levels of drought resistance has not been clearly investigated. Therefore, the aims of this research were to determine whether soil water levels could affect oil quality by changes in fatty acid compositions of peanut, and to investigate the changes in oil characters in peanut genotypes with their potential drought resistance under different water regimes. Field experiments were conducted in split-plot designs with four replications during dry season for two years (2003/04 and 2004/05). Three water regimes [field capacity (FC), 2/3 available soil water (2/3 AW) and 1/3 available soil water (1/3 AW)] were assigned as main-plots, and six peanut genotypes were assigned as sub-plots. The data were recorded at maturity for fatty acid compositions and % oil. Seed samples were analyzed for % oil by Soxtec System HT, and fatty acid compositions were analyzed by gas liquid chromatography. Differences among water regimes and peanut genotypes were significant for oleic and linoleic acids content and their ratio (O/L ratio), unsaturated to saturated fatty acid ratio (U/S ratio) and iodine value (IV). Genotype × water regime interactions were also significant for all characters. Drought improved the oil quality by significant increase in oleic acid and O/L ratio, and reduced the linoleic acid, IV and U/S ratio. Peanut genotypes with different levels of drought resistance displayed similar tendency in fatty acid characters under drought conditions.
[Show abstract][Hide abstract] ABSTRACT: Many plant ESTs have been sequenced as an alternative to whole genome sequences, including peanut because of the genome size and complexity. The US peanut research community had the historic 2004 Atlanta Genomics Workshop and named the EST project as a main priority. As of August 2011, the peanut research community had deposited 252,832 ESTs in the public NCBI EST database, and this resource has been providing the community valuable tools and core foundations for various genome-scale experiments before the whole genome sequencing project. These EST resources have been used for marker development, gene cloning, microarray gene expression and genetic map construction. Certainly, the peanut EST sequence resources have been shown to have a wide range of applications and accomplished its essential role at the time of need. Then the EST project contributes to the second historic event, the Peanut Genome Project 2010 Inaugural Meeting also held in Atlanta where it was decided to sequence the entire peanut genome. After the completion of peanut whole genome sequencing, ESTs or transcriptome will continue to play an important role to fill in knowledge gaps, to identify particular genes and to explore gene function.
Comparative and Functional Genomics 06/2012; 2012:373768. · 1.75 Impact Factor
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[Show abstract][Hide abstract] ABSTRACT: Breeding for terminal drought resistance in peanut can increase their productivity in drought-prone environments and reduce aflatoxin contamination. To improve selection efficiency for superior drought-resistant genotypes, a study of inheritance of traits is worthy, and provides useful information for planning suitable breeding approaches. The objectives of this study were to estimate the heritability of terminal drought resistance traits, the genotypic and phenotypic correlations between drought resistance traits and agronomic traits, and among physiological traits in peanut. The 140 peanut lines in the F 4:6 and F 4:7 generations were generated from four crosses (ICGV 98348 × Tainan 9, ICGV 98348 × KK60-3, ICGV 98353 × Tainan 9, and ICGV 98353 × KK60-3), and tested under well-watered and terminal drought conditions. Field experiments were conducted under the dry seasons 2006/2007 and 2007/2008 in the Northeast of Thailand. Data were recorded for agronomic traits [biomass, pod yield, number of mature pods per plant, seeds per pod, and seed size] and physiological traits [harvest index (HI), SPAD chlorophyll meter reading (SCMR), and specific leaf area (SLA)]. The heritability estimates for physiological traits were higher than for agronomic traits, and varied among crosses. The heritability for HI, SCMR, and SLA ranged from 0.55 to 0.85, 0.72 to 0.91, and 0.61 to 0.90, respectively. Positive correlation between HI and SCMR were significant, and SLA was also found to be inversely associated with SCMR and HI. Significant and positive correlations between HI and SCMR with most of agronomic traits were found. SLA was also negatively correlated with agronomic traits. These results indicated that HI, SLA, and SCMR are potentially useful as indirect selection traits for terminal drought resistance because of high heritability and good correlation with pod yield. Plant breeding approaches using these traits might be effective and valuable for improving terminal drought tolerance in peanut.
SABRAO journal of breeding and genetics 01/2012; 44(2):240-262. · 0.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Construction and improvement of a genetic map for peanut (Arachis hypogaea L.) continues to be an important task in order to facilitate quantitative trait locus (QTL) analysis and the development of tools for marker-assisted breeding. The objective of this study was to develop a comparative integrated map from two cultivated × cultivated recombinant inbred line (RIL) mapping populations and to apply in mapping Tomato spotted wilt virus (TSWV) resistance trait in peanut. A total of 4,576 simple sequence repeat (SSR) markers from three sources: published SSR markers, newly developed SSR markers from expressed sequence tags (EST) and from bacterial artificial chromosome end-sequences were used for screening polymorphisms. Two cleaved amplified polymorphic sequence markers were also included to differentiate ahFAD2A alleles and ahFAD2B alleles. A total of 324 markers were anchored on this integrated map covering 1,352.1 cM with 21 linkage groups (LGs). Combining information from duplicated loci between LGs and comparing with published diploid maps, seven homoeologous groups were defined and 17 LGs (A1-A10, B1-B4, B7, B8, and B9) were aligned to corresponding A-subgenome or B-subgenome of diploid progenitors. One reciprocal translocation was confirmed in the tetraploid-cultivated peanut genome. Several chromosomal rearrangements were observed by comparing with published cultivated peanut maps. High consistency with cultivated peanut maps derived from different populations may support this integrated map as a reliable reference map for peanut whole genome sequencing assembling. Further two major QTLs for TSWV resistance were identified for each RILs, which illustrated the application of this map.
Theoretical and Applied Genetics 11/2011; 124(4):653-64. · 3.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Peanut (Arachis hypogaea L.) is one of the most important oilseed and nutritional crops in the world. To efficiently utilize the germplasm collection, a peanut mini-core containing 112 accessions was established in the United States. To determine the population structure and its impact on marker-trait association, this mini-core collection was assessed by genotyping 94 accessions with 81 SSR markers and two functional SNP markers from fatty acid desaturase 2 (FAD2). Seed quality traits (including oil content, fatty acid composition, flavonoids, and resveratrol) were obtained through nuclear magnetic resonance (NMR), gas chromatography (GC), and high-performance liquid chromatography (HPLC) analysis. Genetic diversity and population structure analysis identified four major subpopulations that are related to four botanical varieties. Model comparison with different levels of population structure and kinship control was conducted for each trait and association analyses with the selected models verified that the functional SNP from the FAD2A gene is significantly associated with oleic acid (C18:1), linoleic acid (C18:2), and oleic-to-linoleic (O/L) ratio across this diverse collection. Even though the allele distribution of FAD2A was structured among the four subpopulations, the effect of FAD2A gene remained significant after controlling population structure and had a likelihood-ratio-based R ( 2 ) (R ( LR ) ( 2 ) ) value of 0.05 (oleic acid), 0.09 (linoleic acid), and 0.07 (O/L ratio) because the FAD2A alleles were not completely fixed within subpopulations. Our genetic analysis demonstrated that this peanut mini-core panel is suitable for association mapping. Phenotypic characterization for seed quality traits and association testing of the functional SNP from FAD2A gene provided information for further breeding and genetic research.
Theoretical and Applied Genetics 08/2011; 123(8):1307-17. · 3.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Germin-like proteins (GLPs) play diversified roles in plant development and defense response. Here, we identified 36 expressed
sequence tags (ESTs) encoding GLPs from peanut (Arachis hypogaea L.). After assembly, these ESTs were integrated into eight unigenes named AhGLP1 to AhGLP8, of which, three (AhGLP1-3) were comprised 14, ten, and seven EST clones, respectively, whereas the remaining ones were associated with one single
clone. The length of the deduced amino acid (AA) residues ranged from 208 to 223 AAs except for AhGLP6 and AhGLP8, which were
incomplete at the carboxyl terminus. All of the AhGLPs contained a possible N-terminal signal peptide that was 17 to 24 residues
in length excluding AhGLP7, where there is likely a non-cleavable amino terminus. Phylogenetic analysis showed that these
AhGLPs were classified into three subfamilies. Southern blot analysis indicated that AhGLP1 and AhGLP2 likely have multiple copies in the peanut genome. The recombinant mature AhGLP1 and AhGLP2 proteins were successfully expressed
in Escherichia coli. The purified AhGLP2 has superoxide dismutase (SOD) activity in enzymatic assay, but not oxalate oxidase activity. The SOD
activity of AhGLP2 was stable up to 70°C and resistant to hydrogen peroxide, suggesting that AhGLP2 might be a manganese-containing
SOD. Furthermore, AhGLP2 could confer E. coli resistance to oxidative damage caused by paraquat, suggesting that the AhGLP2 likely protects peanut plants from reactive
oxygen metabolites. Thus, information provided in this study indicates the diverse nature of the peanut GLP family and suggests
that some of AhGLPs might be involved in plant defense response.
KeywordsPeanut–GLP family–Superoxide dismutase–Oxalate oxidase–Disease resistance