[Show abstract][Hide abstract] ABSTRACT: Peanut, a high-oil crop with about 50% oil content, is either crushed for oil or used as edible products. Fatty acid composition determines the oil quality which has high relevance to consumer health, flavor, and shelf life of commercial products. In addition to the major fatty acids, oleic acid (C18:1) and linoleic acid (C18:2) accounting for about 80% of peanut oil, the six other fatty acids namely palmitic acid (C16:0), stearic acid (C18:0), arachidic acid (C20:0), gadoleic acid (C20:1), behenic acid (C22:0), and lignoceric acid (C24:0) are accounted for the rest 20%. To determine the genetic basis and to improve further understanding on effect of FAD2 genes on these fatty acids, two recombinant inbred line (RIL) populations namely S-population (high oleic line 'SunOleic 97R' × low oleic line 'NC94022') and T-population (normal oleic line 'Tifrunner' × low oleic line 'GT-C20') were developed. Genetic maps with 206 and 378 marker loci for the S- and the T-population, respectively were used for quantitative trait locus (QTL) analysis. As a result, a total of 164 main-effect (M-QTLs) and 27 epistatic (E-QTLs) QTLs associated with the minor fatty acids were identified with 0.16% to 40.56% phenotypic variation explained (PVE). Thirty four major QTLs (>10% of PVE) mapped on five linkage groups and 28 clusters containing more than three QTLs were also identified. These results suggest that the major QTLs with large additive effects would play an important role in controlling composition of these minor fatty acids in addition to the oleic and linoleic acids in peanut oil. The interrelationship among these fatty acids should be considered while breeding for improved peanut genotypes with good oil quality and desired fatty acid composition.
PLoS ONE 04/2015; 10(4):e0119454. DOI:10.1371/journal.pone.0119454 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A reliable peanut root transformation system would be useful to study the functions of genes involved in root biology and disease resistance. The objective of this study was to establish an effective protocol to produce composite plants mediated by Agrobacterium rhizogenes transformation. In total, 75% of transformed peanut seedlings produced an average of 2.83 transgenic roots per plant. Peanut seed had the highest germination rate after treatment in a chlorine gas chamber for 8 h compared with 16 h in chlorine gas or Clorox and mercuric chloride immersion treatments. High transformation efficiency was achieved when the wound site for A. rhizogenes inoculation was covered with vermiculite instead of enclosing the whole plant in a high humidity chamber. On average, 2.5 galls from Meloidogyne arenaria infection were formed per transgenic root from susceptible genotype TifGP-2. These data indicate that A. rhizogenes-transformed roots can be used to phenotype the host response to nematode challenge. Transformation of RLP-2, a candidate resistance gene for M. arenaria integrated into a silencing construct, did not alter the resistance response of Tifguard, even though downregulation of endogenous RLP-2 expression was detected in transformed roots. It is likely that RLP-2 is not the gene conditioning M. arenaria resistance in peanut.
[Show abstract][Hide abstract] ABSTRACT: Tomato spotted wilt, caused by thrips-vectored Tomato spotted wilt virus (TSWV), is a very serious problem in peanut (Arachis hypogaea L) production in the southeastern U.S. Establishment of within row plant densities of 13 or more plants/m of row of moderately resistant cultivars is recommended as part of an integrated management system for minimizing losses to spotted wilt. To achieve that plant density, growers often plant 19 or more seed/m of row. Seed costs represent a major expense for peanut producers. Reducing costs by using lower seeding rates would be desirable if it could be done without increasing risk of losses to tomato spotted wilt. Field experiments were conducted in Tifton, Georgia in 2008 and 2009 to determine whether new cultivars with improved field resistance to TSWV can allow use of lower seeding rates without increasing risk of losses to tomato spotted wilt. In each year, peanut cultivars, Georgia Green, Georgia-06G, Florida-07, and Tifguard were combined factorially with four seeding rates, 9.8, 13.1, 16.4, and 19.7 seed/m of row. Across the two years, final incidence of tomato spotted wilt and standardized area under the disease progress curve for tomato spotted wilt epidemics decreased linearly with increasing seeding rate for all cultivars. Across the two years, final incidence of tomato spotted wilt at 9.8 seed/m of row seeding rate was 55% for Georgia Green and 17% for the mean of the other three cultivars. For Georgia Green, incidence of tomato spotted wilt decreased 1.9% with each seed/m increase in seeding rate, whereas the incremental decrease was 0.8% for the mean of the other three cultivars. These results indicate that levels of field resistance to TSWV in several new cultivars are adequate to allow use of lower seeding rates than with the moderately resistant cultivar Georgia Green without increasing the risk of losses to spotted wilt.
[Show abstract][Hide abstract] ABSTRACT: Drought at pod filling can severely reduce yield of peanut. Better root systems can reduce yield loss from drought. However, the relationship of root characters with yield under terminal drought is not well understood. The objective of this study was to investigate the responses of peanut genotypes with different yield responses to terminal drought stress for root dry weight and the percent root length density (% RLD) in deeper soil layers and their relationships with biological and economic yield. A field experiment was conducted at Khon Kaen University's Agronomy Farm in 2010/2011. and 2011/2012. A split plot design with four replications was used in this study. Five peanut genotypes: ICGV 98308, ICGV 98324, ICGV 98348, Tainan 9 and Tifton 8 were assigned as subplots and two soil moisture levels [field capacity (FC) and 1/3 available water (1/3 AW) at R7 growth stage through harvest] were assigned as main plots. Data for root dry weight, % root length density (% RLD), stomatal conductance, water use efficiency (WUE), pod yield, biomass, harvest index (HI), were recorded at harvest. Drought significantly reduced pod yield, biomass and HI. Overall genotypes, yield responses to terminal drought were not correlated with root dry weight and % RLD. However for some genotypes, yield under terminal drought did seem to be related to root dry weight and % RLD. The genotypes with large root system and high stomata! conductance, WUE and biomass and maintained higher pod yield under terminal drought. For example, Tifton 8 had high root dry weight and high stomatal conductance, WUE and biomass, maintained higher pod yield under drought conditions. Peanut genotypes that have high % RLD at deeper layers and high stomatal conductance, WUE and HI might also maintain pod yield under terminal drought. ICGV 98324 and ICGV 98348 increased % RLD at deeper layers and also had high stomatal conductance, WUE and HI and maintained higher pod yield under terminal drought. Percent RLD could be useful as a selection criterion for improving resistance to drought. However, selection of RLD alone can be confounded because some genotypes with high RLD under terminal drought had low pod yield, and selection of RLD as a supplement for pod yield under drought would be more effective.
Field Crops Research 08/2013; 149:366-378. DOI:10.1016/j.fcr.2013.05.024 · 2.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Peanut (Arachis hypogaea L.) is often grown in climates of intermittent drought on sandy soils. Plants expressing water-conservative traits would minimize exposure to end-of-season, severe drought. Two traits resulting in conservative transpiration rates (TRs) are limitations on TR with soil drying and with increasing vapor pressure deficit (VPD). This study focused on parents of existing recombinant inbred line (RIL) populations as sources of divergent expression of these two traits. If divergence is found, their derived RIL population could be used in identifying genetic markers. Since both water-conservation traits are laborious to document, a key extension of this study was to explore the possibility of using aquaporin inhibitors as practical tools in marker identification. Tifrunner had a lower soil water threshold for a decline in TR than NC 3033 and N08082olJCT. Tifrunner also had a higher VPD breakpoint than three genotypes, including NC 3033 and N08082olJCT. The difference between Tifrunner and these other two genotypes extended to their response to aquaporin inhibitors. The decrease in TR of Tifrunner when exposed to aquaporin inhibitors was much larger than NC 3033 when treated with silver and N08082olJCT when treated with zinc. This study indicates that an effort to develop drought markers in peanut RIL population should focus on Tifrunner x NC 3033 using the silver inhibitor and/or Tifrunner x N08082olJCT using the zinc inhibitor.
[Show abstract][Hide abstract] ABSTRACT: Improvement of N2 fixation might be an effective strategy in peanut breeding for high yield under drought stress conditions. However, under water limited conditions peanut varieties having high water-use efficiency (WUE) are favorable. A pot experiment was conducted under greenhouse conditions at Khon Kaen University, Thailand during December 2002 to May 2003, and repeated during June 2003 to November 2003. Twelve peanut genotypes were tested under three water regimes to estimate the relationships between N2 fixed with biomass production, WUE and pod yield under drought stress conditions. N2 fixed biomass production; pod yield and WUE were reduced by drought stress. At 2/3 AW, Tifton-8 and KK 60-3 were the best genotypes for high N2 fixed and high WUE. ICGV 98324 and ICGV 98300 had high pod yield, whereas Tifton-8 had low pod yield. N2 fixed was positively correlated with biomass and WUE under mild drought conditions but negatively correlated with pod yield. Tifton-8 was the best genotype for N2 fixed and WUE, but it was a poor performer for pod yield under drought conditions. ICGV 98324 and ICGV 98300 had higher pod yield with lower N2 fixed and WUE than did Tifton-8. Results indicated that N2 fixed under drought conditions contributed to vegetative growth and water use efficiency rather than to pod yield. Improvement for high N2 fixed in peanut could lead to high biomass production and WUE but may not necessarily improve pod yield under drought stress conditions.
International Journal of Plant Production 01/2013; 7(2):225-242. · 0.77 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: 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: The dynamic challenges of peanut (Arachis hypogaea L.) farming demand a quick response from breeders to develop new cultivars, a process that can be aided by the application of molecular markers. With the goal to pyramid nematode resistance and the trait for high oleic: linoleic acid (high O:L) ratio in seeds, nematode-resistant cultivar Tifguard was used as the recurrent female parent and high O: L cultivars Georgia-02C and Florida-07 were used as donor parents for the high O:L trait. 'Tifguard High O/L' was generated through three rounds of accelerated backcrossing using BCnF1 progenies selected with molecular markers for these two traits as the pollen donors. Selfed BC3F2 plants yielded marker-homozygous individuals identified as Tifguard High O/L, compressing the hybridization and selection phases of the cultivar development process to less than 3 yr. The accuracy of marker-assisted selection (MAS) was confirmed by phenotyping a subset of F-2:3 populations from both parental combinations. Once additional molecular markers linked with traits of interest are designed to be compatible with high-throughput screening platforms, MAS will be more widely integrated into peanut breeding programs.
The Plant Genome 07/2011; 4(2):110. DOI:10.3835/plantgenome2011.01.0001 · 3.93 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
[Show abstract][Hide abstract] ABSTRACT: With 1 figure and 4 tables
Terminal drought induces preharvest aflatoxin contamination (PAC) in peanut. Drought resistance traits are promising as indirect selection tools for improving resistance to PAC. The objectives of this study were to determine the effects of terminal drought on PAC and to investigate the associations between surrogate traits for drought tolerance and PAC. Field tests under rainout shelters were conducted in the dry seasons 2004/2005 and 2005/2006. Eleven peanut genotypes were evaluated under irrigated and terminal drought conditions. Data were recorded for physiological traits, total biomass, pod yield, Aspergillus flavus colonization and PAC. ICGV 98305, ICGV 98330, ICGV 98348, ICGV 98353 and Tifton-8 had low aflatoxin contamination in both years. Traits related to drought resistance were associated well with those related to PAC under drought conditions. Specific leaf area, relative water content, chlorophyll density and drought stress ratings are the best traits for use as indirect selection tools for lower PAC. Breeding for drought tolerance using these traits as selection criteria may help to accelerate progress in developing resistance to PAC.
[Show abstract][Hide abstract] ABSTRACT: Twelve peanut genotypes were tested under three water regimes in two greenhouses to investigate the effects of drought on biomass production and N<SUB>2</SUB> fixation. Drought reduced biomass production from 36.5 to 56.0% and reduced nitrogen fixation from 26.8 to 68.8%. Most genotypes with high biomass production under Field Capacity (FC) had high reduction in biomass production under drought conditions, but fewer genotypes with high N<SUB>2</SUB> fixed under FC showed high reduction in N<SUB>2</SUB> fixed. Biomass production under FC in general gave more contribution to biomass production under drought conditions than did the reduction. N<SUB>2</SUB> fixed under FC and the reduction in N<SUB>2</SUB> fixed contributed similarly to N<SUB>2</SUB> fixed under drought conditions. Positive and significant correlations between N<SUB>2 </SUB>fixed and biomass production were found at FC and 2/3 available soil water (AW), but the correlation was not significant at 1/3 AW. Tifton-8 was the best genotype for high N<SUB>2</SUB> fixed under FC and KK 60-3 was the best genotype for low reduction. Correlations between N<SUB>2</SUB> fixed and nodule dry weight and shoot dry weight were high and consistent across water regimes. This information is important for breeders to develop peanut cultivars with reasonably high nitrogen fixation under drought conditions.
Asian Journal of Plant Sciences 07/2010; 9(7). DOI:10.3923/ajps.2010.402.413
[Show abstract][Hide abstract] ABSTRACT: In 2001, entries from the peanut core collection, a subset of the USDA peanut germplasm collection, were planted in non-replicated plots in a field with a history of Sclerotinia blight caused by Sclerotinia minor. Variability existed among entries for reaction to Sclerotinia blight. Of the 744 entries evaluated, 11% had no disease, nearly 30% had <10% disease incidence, and only 21% had 50% disease incidence or more. Most of the resistant entries had an upright growth habit and were in early and mid-maturity groups. Many of the early maturing entries were susceptible to the foliar disease pepper spot which occurred throughout the study. Entries were selected for further evaluation in replicated plots based on a nil to low (<10%) incidence of Sclerotinia blight, adaptation and/or vigor, and other desirable characteristics such as an intermediate to prostrate growth habit and pepper spot resistance. Selected entries were retested in both 2002 and 2003 (n = 62) and compared to resistant (Tamspan 90), moderately resistant (Tamrun 96), and susceptible (Okrun) reference cultivars. Most entries (55 in 2001 and 46 in 2003) had disease incidence less than Tamrun 96 and similar to Tamspan 90. In 2003 when disease incidence was highest, all 46 entries with resistant reactions similar to that of Tamspan 90 had erect plant growth habits except for entries 208 and 582 which were prostrate, and entries 273, 128, and 804 which were intermediate. Resistance to Sclerotinia blight and yield similar to Tamspan 90, plant habit, and/or reactions to pepper spot and web blotch were used to select the best entries. Entries 208, 128, 804, 582, and 273 combined resistance to Sclerotinia blight, pepper spot, and web blotch with less than erect growth habits. Entry 103 had good Sclerotinia blight resistance and yield, but an upright growth habit. Entry 92 had an upright growth habit and low yield, but good Sclerotinia blight resistance. Entries 92 and 103 had upright growth habits but were among the best entries for resistant to pepper spot and web blotch. Entries 426, 184, and 562 were upright and susceptible to pepper spot, but had resistance to web blotch and the best resistance to Sclerotinia blight. These entries appear to be useful sources of resistance to Sclerotinia blight for breeding programs and for increasing the probability of finding additional sources of resistance in clusters of germplasm identified within the entire USDA collection.