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Different peanut yields under terminal drought might be due to the different nutrient uptakes among peanut genotypes. Nutrient uptake was presumed to be a drought-resistant trait and might involve drought tolerance mechanisms. The aims of this study, therefore, were to characterize the effect of terminal drought on peanut nutrient uptake and to investigate the genotypic variability of nutrient uptake and its interactions with terminal drought. Field experiments were conducted at the Field Crop Research Station of Khon Kaen University, Khon Kaen, Thailand, from October 2010 to January 2011 and October 2011 to January 2012. Six peanut genotypes were tested under well-watered and terminal drought conditions. Data were recorded for N, P, K, Ca, and Mg uptake and biomass (BM) and pod yield (PY); the ratio of nutrient uptake under stress condition was calculated. Terminal drought significantly reduced nutrient uptake in both years, and peanut genotypes differed considerably with respect to nutrient uptakes under well-watered and terminal drought conditions. ICGV 98324 and ICGV 98348 were the best genotypes for nutrient uptake under terminal drought. Tainan 9 and Tifton 8 had low nutrient uptake under both conditions. ICGV 98308 and Tifton 8 had medium uptake and Tainan 9 had the lowest. Significant correlations between nutrient uptakes and BM and PY were mostly observed under well-watered and drought conditions. Based on nutrient uptake, ICGV 98324 and ICGV 98348 were identified as drought-tolerant lines. These genotypes could maintain high nutrient uptakes across water regimes; consequently, these traits can also be used as efficient tools for selecting peanut genotypes with terminal drought tolerance.

The objective of this study was to investigate the responses of peanut genotypes to midseason drought, regarding in particular nutrient uptakes and their correlations with biomass production and pod yield. The experiment was conducted during the dry seasons of 2011/12 and 2012/13. Five peanut genotypes with different levels of drought tolerance and 2 water regimes (well-watered and midseason drought) were laid out in a split-plot design with 4 replications. Midseason drought was imitated by stopping irrigation at 30 days after planting (DAP) and then rewatering at 60 DAP. The data were recorded for contents of N, P, K, Ca, and Mg in plant tissues, biomass production, yield components, and pod yield at harvest. The results showed that midseason drought significantly reduced the uptake of all nutrient elements. Peanut genotypes with higher levels of drought tolerance took up more nutrients than those with lower levels. The uptake of all nutrient elements contributed to biomass production, pod yield, and the number of pods per plant. ICGV 98305 was the best genotype with the highest uptakes of all observed nutrient elements.

Efficacy of Trichoderma harzianum and the arbuscular mycorrhizal fungus (AMF) Glomus clarum for suppression of southern stem rot caused by Sclerotium rolfsii in Jerusalem artichoke was investigated in Thailand under greenhouse conditions. Experimental factors included two Jerusalem artichoke genotypes (HEL 246 and JA 37), two levels of T. harzianum and G. clarum (inoculated and blank). The biological control agents were added to the potting medium immediately before seedlings of Jerusalem artichoke were transplanted into it; 20 days later, seedlings were inoculated with S. rolfsii by placing infested sorghum seeds at the base of the stem. The combination of cv. HEL 246 with addition of both G. clarum and T. harzianum had the lowest disease incidence (30%) and required the longest time to permanent wilt (11 days after inoculation). Inoculation of cv. JA 37 and HEL 246 with G. clarum alone gave better control of the disease than did inoculation with T. harzianum alone. The results are the first published report of biological control of S. rolfsii on Jerusalem artichoke.

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 stomatal 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.

Jerusalem artichoke (Helianthus tuberosus L.) is an important tuber crop. However, Jerusalem artichoke seeds contain high levels of starch and lipid, making the extraction of high-quality RNA extremely difficult and the gene expression analysis challenging. This study was aimed to improve existing methods for extracting total RNA from Jerusalem artichoke dry seeds and to assess the applicability of the improved method in other plant species. Five RNA extraction methods were evaluated on Jerusalem artichoke seeds and two were modified. One modified method with the significant improvement was applied to assay seeds of diverse Jerusalem artichoke accessions, sunflower, rice, maize, peanut and marigold. The effectiveness of the improved method to extract total RNA from seeds was assessed using qPCR analysis of four selected genes. The improved method of Ma and Yang (2011) yielded a maximum RNA solubility and removed most interfering substances. The improved protocol generated 29 to 41 µg RNA/30 mg fresh weight. An A260/A280 ratio of 1.79 to 2.22 showed their RNA purity. Extracted RNA was effective for downstream applications such as first-stranded cDNA synthesis, cDNA cloning and qPCR. The improved method was also effective to extract total RNA from seeds of sunflower, rice, maize and peanut that are rich in polyphenols, lipids and polysaccharides.

A better understanding of the mechanisms of peanut adaptation to pre-flowering drought is important for improving pod yield productivity. Nevertheless, the mechanisms of drought tolerance are under different genetic controls, and pod yield is a complex trait. Therefore, the aim of this study was to investigate the mechanism for drought tolerance of peanut genotypes with different pod yield responses under pre-flowering drought conditions. Field experiments were conducted during February to July, 2007 and during February to July, 2009. A split-plot experiment in a randomized complete block design was used. Two water management treatments were assigned as the main plots, i.e. field capacity (F.C.) and pre-flowering stress (PFD), and six peanut genotypes as the sub-plots. Relative water content (RWC) and stomatal conductance were recorded at 5, 10, 15, 20, 25, 30, 35 and 40 days after emergence (DAE). Leaf area index was measured at 25 DAE, R5 and R7. Total dry matter samples, including shoots, roots and pods, were obtained at 25 DAE, R5, R7 and harvest. Shoot growth rate, root growth rate and pod growth rate were then calculated. Major finding, the first mechanism is explained by high water uptake of the root systems that provide sufficient water for normal transpiration, as the response of ICGV 98305 to PFD. It may induce the improvement of peanut pod growth rate in pod filling stage due to the change of assimilate proportion, resulting in increasing pod yield to PDF comparing with adequate water conditions. In contrast, such as the response of ICGV 98330, pre-flowering drought can increase the ability of peanut to save more water by reduction of transpiration, but rooting traits are not changed. This could conserve more water by reducing transpiration to maintain high RWC. Nevertheless, the ability to reduce transpiration did not support the improvement of peanut pod yield under these conditions. The increasing peanut productivity to pre-flowering drought was contributed by the improvement of assimilate proportion to economic part in reproductive phase. This knowledge will be useful for breeding of peanut for pre-flowering drought environment.

Influences of harvest time and storage conditions on activities of fructan:fructan1-fructosyltransferase (1-FFT) and inulin hydrolase (InH) in relation to inulin and soluble sugars of Jerusalem artichoke (Helianthus tuberosus L.) tubers were investigated. Maturity affected 1-FFT-activity, inulin contents, and inulin profiles of the tubers harvested between 30 and 70 days after flowering (DAF). Decreases in 1-FFT activity, high molecular weight inulin, and inulin content were observed in late-harvested tubers. The tubers harvested at 50 DAF had the highest inulin content (734.9 ± 20.5 g kg−1 DW) with a high degree of polymerization (28% of DP >30). During storage of the tubers, increases in InH activity (reached its peak at 15 days of storage) and gradual decreases in 1-FFT activity took placed. These changes were associated with inulin depolymerization, causing decreases in inulin content and increases in soluble sugars. As well, decreasing storage temperatures would retain high inulin content and keep low soluble sugars; and freezing at −18 °C would best retard 1-FFT, InH, and inulin changes.

Drought is a recurring problem of Jerusalem artichoke (Helianthus tuberosus L.) production under rainfed conditions. A better understanding of the responses of Jerusalem artichoke genotypes to drought can lead to the improvement of inulin content and inulin yield in Jerusalem artichoke and its production planning. The objective of this study was to compare the responses of five Jerusalem artichoke genotypes (JA60, JA125, JA5, JA89, and HEL65) to three water regimes (100% available water (AW; field capacity), 50% AW, and 25% AW) for inulin content and inulin yield. The experimental results showed that water regimes and Jerusalem artichoke genotypes were significantly different for inulin content and inulin yield. The interactions between Jerusalem artichoke genotypes and water regimes were also significant for inulin content and inulin yield. Under field capacity level, the results from the experimental years (2012 and 2013) showed that JA125, JA5, JA60, and HEL65 had the highest inulin content. Under 50% and 25% AW, JA5 and HEL65 had high inulin content, while JA5 had the highest inulin yield. The results indicated that if irrigation is available, JA5 should be planted because of its high inulin content under well-irrigated conditions. However, JA5, JA125, and JA60 are highly recommended under rainfed conditions because of their high inulin content under drought conditions. The results were limited to a pot experiment, and further field experiments are still required.

Epigenetic histone modifications are considered as a promising avenue for cancer preventive and therapeutic strategies. The purpose of this study was to evaluate the antiproliferative and histone deacetylase (HDAC) inhibitory activity of selected peanut phenolics, including p-coumaric acid, ferulic acid, sinapinic acid and resveratrol, in MCF-7 and HeLa cells. The cytotoxic and HDAC inhibitory activities were assessed by MTT assays, flow cytometric analyses of cell cycle arrest and apoptosis induction, and western blotting. The results showed that all four phenolics inhibited proliferation of both MCF-7 and HeLa cells in a dose-dependent manner. Among the phenolics tested, resveratrol was the most effective in inhibiting growth of cancer cells. Treatment with all phenolics resulted in histone H3 hyperacetylation in both cell lines, indicating potential for HDAC inhibition. These phenolics induced apoptosis in both MCF-7 and HeLa cells in a concentration-dependent manner. Moreover, all phenolics induced G0/G1-phase arrest of the cell cycle in MCF-7 cells while p-coumaric and ferulic acids caused S-phase arrest in HeLa cells. Exposure to p-coumaric acid increased p53 and p21 expression but decreased CDK4 levels in both cell types, which could result in the observed G0/G1 arrest. Moreover, inhibition of ERK1/2 phosphorylation by ferulic acid and resveratrol contributed to cell growth inhibition. Peanut phenolics appear to influence the extent of histone acetylation in MCF-7 and HeLa cells, and this activity modulates multiple pathways that are implicated in cancer prevention.

A successful peanut breeding to obtain genotypes with greater phenolic content requires information on type and content of phenolic compounds in parental peanut genotypes. The aim of this study was to investigate the total phenolic contents and phenolic acid profiles of 15 Valencia-type peanut genotypes both in peanut testae and testa-removed kernels (cotyledons and embryonic axes). Total phenolic content and phenolic acid profiles were analyzed using Folin-Ciocalteu method and high-performance liquid chromatography (HPLC), respectively. The total phenolic contents of testae and testa-removed kernels varied from 2.47 ± 0.96 to 84.53 ± 5.57 and 0.07 ± 0.01 to 0.12 ± 0.01 mg gallic acid equivalent (GAE)/g dry weight, respectively. Testae of KK4 and ICG14710 genotypes had the greatest and least total phenolic content, respectively. The peanut testae with pink color (NM044, NM071, ICG15042 and KK4) had significantly greater phenolic content than those with gray (ICG397 and ICG14710) and yellow (NM001) colors. The present study demonstrates that p-coumaric and vanillic acids were the two predominant phenolic acids in the testae of nearly all peanut genotypes tested, except for KK4 genotype whose predominant phenolic acid in its testa was p-hydroxybenzoic acid. All the testa-removed kernels tested contained significantly greater amount of p-coumaric acid than other identified phenolic acids. These results would be useful for peanut breeding to obtain peanut genotypes with greater phenolic acid and other favorable traits. Key words: Valencia peanuts, peanut testae, phenolic acids, p-coumaric acid , vanillic acid.

Southern stem rot caused by Sclerotium rolfsii is a significant problem of Jerusalem artichoke (Helianthus tuberosus L.) production in Thailand. Resistant varieties are not available. The objective of this study was to investigate genetic variability of Jerusalem artichoke genotypes for resistance to stem rot caused by S. rolfsii. Ninety-one Jerusalem artichoke genotypes were evaluated under greenhouse conditions. Traits evaluated included disease score, lesion length, days to permanent wilting, plant height, shoot dry weight, and root dry weight index. Number of days from inoculation until permanent wilting was the only trait with statistically significant differences among genotypes. Based on this trait, genotypes were categorized into two distinct groups: resistant and susceptible. Genotypes that consistently expressed relative resistance to S. rolfsii included HEL 280, HEL 278, HEL 293 and JA 98. These genotypes may be useful to plant breeders as sources of germplasm for incorporating resistance to S. rolfsii into Jerusalem artichoke.

Jerusalem artichoke is a diversely-utilized crop. Selection for high yield, inulin content and other economically important traits are useful for improving this crop. The objectives of the present study were to evaluate genetic variability for qualitative and quantitative traits among Jerusalem artichoke accessions and to identify different groups of accessions using morphological and agronomic traits. Seventy-nine accessions were evaluated in a randomized complete block design with two replications in the late rainy season 2008, the early rainy season 2009 and the late rainy season 2009 at Khon Kaen University agronomy farm, Thailand. Morphological and agronomic characteristics were evaluated for genetic variations. High variations were found among Jerusalem artichoke accessions for qualitative and quantitative characters, and selection for these characters is possible. High variations were observed for tuber width, number of tubers/plant, biomass, fresh tuber yield and tuber size. Correlation coefficient between fresh tuber yield and tuber size was positive and significant (0.58, P ≤ 0.01). Improvement of tuber size is a means to improve yield and tuber quality. Based on morphological and agronomic characteristics, Jerusalem artichoke accessions were clustered into four distinct groups (R2 = 0.88). These groups may be used as parental material to generate progenies for further improvement of this crop. This information will enable breeders to make informed decisions about possible heterotic groups for their breeding programs and germplasm conservation.

Peanut root distribution patterns are not well understood and have not been studied extensively. There is a lack of information on the classification of root distribution patterns for many peanut genotypes and the relationship between rooting traits and yield under mid-season drought, which could be useful for breeding for drought tolerance. In this study the root distribution of 40 peanut genotypes with different drought tolerance levels and different sources of origin was evaluated during the dry seasons of 2007 and 2008 at Khon Kaen University, Thailand. A randomized complete block design with four replications was used in both years. All plots were well-irrigated except when water was withheld from 50 to 83 days after planting (DAP) during the first season and from 50 to 87 DAP during the second season to emulate a mid-season drought. Top dry weight was observed at the most water-stressed date and at harvest, while root data were measured at the most water-stressed date using the auger method. The soil was sampled to a depth of 90 cm and was separated into the upper (0–30 cm), middle (30–60 cm) and deeper (60–90 cm) soil layers. For each peanut genotype, the relative contribution to each layer was calculated and defined as root length density percentage (%RLD). Pod yield was observed at final harvest date and pod harvest index (PHI) was calculated as pod dry weight per unit of total biomass. The forty peanut genotypes were categorized as either high or low %RLD depending on the mean of %RLD in each layer for the three soil layers. These peanut genotypes were then categorized into six combinative groups, based on the high vs. low %RLD for each of the three layers. The relationship between %RLD in the lower soil layer and yield was significant and positive for both seasons, indicating that %RLD in the lower layer is an important trait that affects pod yield under mid-season drought conditions. There was a negative relationship to %RLD in the upper layer in one season and no relationship to %RLD in the middle soil layer for both seasons. The results from this study also indicated that PHI was an important trait that is associated with maintaining pod yield under mid-season drought.

This work aims to establish characteristic SDS-PAGE profiles of peanut seed albumins and prolamins associated with Aspergillus flavus resistance assay. Comparing to the traditional method, a successful alternate method was developed by sequential extraction with 2 M NaCl in buffer (pH 6.8), 70% ethanol and w ter. The alcohol-soluble prolamin fraction from the present method showed unique profiles possessing antifungal activity against spore germination and mycelial growth. The water-soluble albumin fraction had specific profiles and demonstrated inhibition only on mycelial growth. Yet, the salt-soluble globulin fraction enhanced both processes of A. flavus propagation.

Genetic variations in germplasm and genotype × environment interaction (G × E) are important for crop improvement. The objectives were to explore genetic variation in Jerusalem artichoke germplasm and to evaluate G × E interaction for inulin content. Seventy-nine accessions of Jerusalem artichoke were evaluated in a randomized complete block design with two replications for three seasons. Significant variation in inulin content (55.3–74.0% dry weight) was observed and the genotypes with high inulin content could be identified although there was intermediate G × E interaction. Genotypes were also significantly different for days to maturity, fresh tuber yield, biomass and harvest index and G × E interactions for these traits were also significant. The correlation between inulin content and days to maturity was not significant (r = −0.20), whereas inulin content and fresh tuber yield were significantly associated (r = 0.22). JA 37 and CN 52867 are promising for high yield and inulin content.

A simple spectrophotometric method was developed for the analysis of inulin in Jerusalem artichoke tubers. The inulin was extracted from the artichoke tuber samples using accelerated solvent extraction method, before subsequent hydrolysis in acid condition. The hydrolysates were then analyzed for fructose using spectrophotometry. The spectrophotometric method is based on oxidation of fructose by periodate and evaluation of the remaining periodate by measuring the absorbance at 350 nm of the tri-iodide complex formed, upon addition of potassium iodide. The optimum conditions for the detection of fructose were 0.1 mmol L−1 periodate and 1.5 mmol L−1 potassium iodide at pH 6.0. The proposed method was validated for its analytical performance parameters including accuracy, precision, and recovery. The method was applied to the determination of inulin in ten varieties of Jerusalem artichoke grown in the northeastern part of Thailand. The inulin content in the samples was found to be in the range of 63–75.5% dry weight, and the degree of polymerization was in the range of 14–20. The inulin contents obtained from the proposed spectrophotometry were not significantly different (p = 0.05) from those obtained from high-performance anion-exchange chromatography coupled with pulsed amperometric detection. The results indicated that the present spectrophotometric method can be used as an alternative to chromatographic analysis for the determination of inulin in plant samples.

Jerusalem artichoke (Helianthus tuberosus L.) is an old tuber crop with a recently renewed interest in multipurpose improvement, but little effort has been made to characterize its genetic resources. A study was conducted to assess genetic structure and genetic relatedness of 47 diverse Jerusalem artichoke accessions using RAPD, ISSR and SRAP markers. A total of 296 (87.1%) polymorphic bands were detected from 13 RAPD markers; 92 (80%) from six ISSR primers; and 194 (88.6%) for nine combinations of SRAP primers. Five optimal clusters were inferred by the STRUCTURE program from the RAPD or ISSR data, while six optimal clusters were found from the SRAP data or combined marker data. Significant linear relationships between the distance matrices for all pairs of individual accessions were detected for all marker pairs and the estimated correlation coefficient was 0.40 for RAPD-ISSR, 0.53 for RAPD-SRAP, and 0.43 for ISSR-SRAP. Based on the combined data, the neighbor-joining clustering of the 47 accessions matched closely with those inferred from the STRUCTURE program. Three ancestral groups were observed for the Canadian germplasm. Most diverse germplasm harbored in the USA collection. These findings not only reveal the compatible patterns of genetic structure and relatedness inferred with three marker types, but also are useful for managing Jerusalem artichoke germplasm and utilizing diverse germplasm for genetic improvement.

Water stress during the vegetative development normally is not detrimental and sometimes actually increases yield of peanut (Arachis hypogaea L.). Root growth might play an important role in response to early season drought in peanut and might result in an increase in yield. Information on the response of root characters of diverse peanut genotypes to these conditions will provide useful information for explaining mechanisms and improving peanut genotypes for exploiting positive interaction for pod yield under pre-flowering drought. The aim of this study, therefore, was to investigate the root dry weight and root length density of peanut genotypes with different yield responses to pre-flowering drought stress and their relationships with pod yield. Field experiments were conducted at the Field Crop Research Station of Khon Kaen University, Khon Kaen, Thailand during February to July 2007 and during February to July 2009. A split-plot experiment in a randomized complete block design was used. Two water management treatments were assigned as the main plots, i.e. field capacity and pre-flowering stress, and six peanut genotypes as the sub-plots. Total crop dry matter, root dry weight and root length density were recorded at 25 DAE, R5 and R7. Top dry weight and pod yield were measured at harvest and pod harvest index (PHI) was computed using the data on pod yield and biomass. Peanut genotypes were categorized into three groups based on their responses to drought for pod yield, e.g. increasing, decreasing and non-responsive groups. The genotypes of each group showed a differential response for root quantity and distribution. The increasing pod yield group had more root dry weight and root length density in the deeper soil layers during pre-flowering stress compared to the non-stress treatment. The non-responsive group showed no root response under pre-flowering drought conditions compared to the non-stress treatment. A larger root system alone without considering distribution may not contribute much to pod yield but a higher RLD at deeper layers may allow plants to mine more available water in the sub-soil. However, as yield is a complex trait, several mechanisms may be involved. The increasing pod yield group also had the ability to maintain a high PHI.

The rapid accumulation and conversion of the dry matter into harvestable yield under limited crop duration are preferable for peanut (Arachis hypogaea L.) grown in various cropping systems where intensified cropping systems are generally practiced. In these cropping systems, peanut genotypes with acceptable yield and shorter crop duration are required. The objectives of this study were to estimate the broad sense heritability for Crop Growth Rate (CGR), Pod Growth Rate (PGR), Partitioning Efficiency (PC) and reproductive duration in an advanced generation of segregating population of large-seeded type peanut and to investigate the relationship among these characters. Two-hundred breeding lines in the F6 generation of 10 peanut crosses (twenties for each cross) were assigned in a randomized complete block design with two replications. CGR, PGR, PC and RD were recorded at harvest. Heritability estimates for CGR (0.00-0.60) were lower than those for PGR (0.04-0.68), PC (0.00-0.82) and RD (0.17-0.90). Correlation coefficients among CGR, PGR and PC were positive and significant, whereas they were negatively and significantly correlated with RD. The results suggested that improvement of CGR, PGR, PC would be possible among studied materials and would result in lower reproductive duration and early maturity

The use of the surrogate traits with simple inheritance as selection criteria for drought tolerance should speed up the selection programs. The objectives of this study were to investigate the responses of released cultivars of peanut to end of season drought for traits related to drought tolerance and agronomics traits and to identify the released cultivars with tolerance to end of season drought. Ten peanut genotypes and two water regimes (field capacity; FC and 1/3 available water; 1/3 AW) were laid out in a split plot design with four replications for two years. The data were recorded for SPAD chlorophyll meter reading (SCMR), Specific leaf weight (SLW), biomass, pod yield, harvest index (HI), number of mature pods, 100-seed weight and number of seeds per pod. Drought increased SCMR and SLW and reduced biomass production, pod yield and seed size, whereas harvest index and number of pods per plants were not significantly affected. Maintaining high pod yield and number of pods per plant depended solely on high potential under well-watered conditions, whereas maintaining high biomass production and seed size and harvest index was dependent on both high potential and low reduction. SCMR and SLW were well associated and they had high correlations with biomass and pod yield. SCMR seemed to be more stable than SLW and it is recommended to be used as a surrogate trait for drought tolerance in peanut. The released cultivar KKU 60 was identified as drought tolerant by SCMR and SLW and by pod yield

The difference in PBND incidence in the rainy and dry seasons in Thailand has led to a hypothesis that temperature and relative humidity might be the causal factors. The objective of this study was to investigate the effects of temperature and relative humidity on the effectiveness of mechanical inoculation of PBNV on peanut. Two experiments were conducted in the rainy and dry seasons during 2004 to 2005, using the susceptible peanut genotype Tainan 9. The first experiment evaluated the effect of low temperature on the effectiveness of PBNV transmission by mechanical inoculation. The second experiment compared two temperature and relative humidity conditions in the rainy season and in the dry season. The results showed that exposing the PBNV-inoculated plants to low temperature (25°C, 90% RH) during a 12 h light period and 20°C, 90% RH during a 12 h dark period) for all the time during the experimental period did not increase the infected plants. Two climate conditions representing the dry season (daytime, 32°C, 44% RH, night-time, 22°C, 65% RH) and the rainy season (daytime, 36°C, 46% RH, night-time, 25°C, 70% RH) in Thailand also showed no difference in the infected plants. These results indicated that low temperature or relative humidity did not affect the transmissibility of PBNV. The difference in disease incidences in the rainy and the dry seasons in Thailand could not be explained by the difference in climatic conditions but could possibly be accounted for by the difference in vector infestation

Twelve peanut genotypes were tested under three water regimes in two greenhouses to investigate the effects of drought on biomass production and N2 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 N2 fixed under FC showed high reduction in N2 fixed. Biomass production under FC in general gave more contribution to biomass production under drought conditions than did the reduction. N2 fixed under FC and the reduction in N2 fixed contributed similarly to N2 fixed under drought conditions. Positive and significant correlations between N2 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 N2 fixed under FC and KK 60-3 was the best genotype for low reduction. Correlations between N2 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

Oleic acid in peanut oil increases shelf-life and kernel quality. Heritability for oleic acid is important for predicting selection progress. The aims of this study were to estimate the heritability of oleic acid content by parent-offspring regression and to determine the correlation among oil characters. The data were collected in the F2 and F3 generations derived from the crosses between two high-oleic peanuts (SunOleic 97R and Georgia-02C) and a low oleic peanut (KKU 1). The F2 populations were planted in the rainy season (2008) and the F3 populations derived from the F2 populations were planted in the dry season (2008/09) at Khon Kean University. Heritability estimates in narrow sense were intermediate to high for oleic and linoleic acids (0.63-0.72 and 0.57-0.72, respectively). Heritability estimates for % oil were low in all populations. Significant and negative correlation was observed between oleic and linoleic acids (r = -0.98). The high heritability for oleic acid in this study indicated that selection for high oleic acid in peanut was effective in the F2 generation

More rapid progress in breeding peanut for reduced aflatoxin contamination should be achievable with a better understanding of the inheritance of, aflatoxin trait and physiological traits that are associated with reduced contamination. The objectives of this study were to estimate the heritability of aflatoxin traits and genotypic (rG) and phenotypic (rP) correlations between drought resistance traits and aflatoxin traits in peanut. One hundred-forty peanut lines in the F4:6 and F4:7 generations were generated from four crosses, and tested under well-watered and terminal drought conditions. Field experiments were conducted under the dry seasons 2006/2007 and 2007/2008. Data were recorded for biomass (BIO), pod yield (PY), drought tolerance traits [harvest index (HI), drought tolerance index (DTI) of BIO and PY, specific leaf area (SLA), and SPAD chlorophyll meter reading (SCMR)], and aflatoxin traits [seed infection and aflatoxin contamination]. Heritabilities of A. flavus infection and aflatoxin contamination in this study were low to moderate. The heritabilities for seed infection and aflatoxin contamination ranged from 0.48 to 0.58 and 0.24 to 0.68, respectively. Significant correlations between aflatoxin traits and DTI (PY), DTI (BIO), HI, biomass and pod yield under terminal drought conditions were found (rP = −0.25** to 0.32**, rG = −0.57** to 0.53**). Strong correlations between SLA and SCMR with A. flavus infection and aflatoxin contamination were also found. Positive correlations between SLA at 80, 90, and 100 DAP and aflatoxin traits were significant (rP = 0.13** to 0.46**, rG = 0.26** to 0.81**). SCMR was negatively correlated with aflatoxin traits (rP = −0.10** to −0.40**, rG = −0.11** to −0.66**). These results indicated that physiological-based selection approaches using SLA and SCMR might be effective for improving aflatoxin resistance in peanut.

Drought during the pre-flowering stage can increase yield of peanut. There is limited information on genotypic variation for tolerance to and recovery from pre-flowering drought (PFD) and more importantly the physiological traits underlying genotypic variation. The objectives of this study were to determine the effects of moisture stress during the pre-flowering phase on pod yield and to understand some of the physiological responses underlying genotypic variation in response to and recovery from PFD. A glasshouse and field experiments were conducted at Khon Kaen University, Thailand. The glasshouse experiment was a randomized complete block design consisting of two watering regimes, i.e. fully-irrigated control and 1/3 available soil water from emergence to 40 days after emergence followed by adequate water supply, and 12 peanut genotypes. The field experiment was a split-plot design with two watering regimes as main-plots, and 12 peanut genotypes as sub-plots. Measurements of N-2 fixation, leaf area (LA) were made in both experiments. In addition, root growth was measured in the glasshouse experiment. Imposition of PFD followed by recovery resulted in an average increase in yield of 24 % (range from 10 % to 57 %) and 12 % (range from 2 % to 51 %) in the field and glasshouse experiments, respectively. Significant genotypic variation for N-2 fixation, LA and root growth was also observed after recovery. The study revealed that recovery growth following release of PFD had a stronger influence on final yield than tolerance to water deficits during the PFD. A combination of N-2 fixation, LA and root growth accounted for a major portion of the genotypic variation in yield (r = 0.68-0.93) suggesting that these traits could be used as selection criteria for identifying genotypes with rapid recovery from PFD. A combined analysis of glasshouse and field experiments showed that LA and N-2 fixation during the recovery had low genotype x environment interaction indicating potential for using these traits for selecting genotypes in peanut improvement programs.

Drought tolerance can be an effective tool for improving aflatoxin resistance in peanut. We evaluated 140 peanut families from 4 crosses in the F 4:7 and F 4:8 generations in field trials under drought and non–drought conditions to investigate the heritability ( h 2 ) of aflatoxin resistance traits, and phenotypic ( r P ) and genotypic ( r G ) correlations between aflatoxin resistance and drought tolerance traits. Data were collected for seed infection by Aspergillus flavus , aflatoxin contamination, biomass, pod yield, drought tolerance index (DTI) of biomass (BIO), DTI of pod yield (PY), harvest index (HI), SPAD chlorophyll meter reading (SCMR) and specific leaf area (SLA). High genotype x environment interactions and low to moderate h 2 for seed infection and aflatoxin contamination (0.30 to 0.65) were observed, indicating difficulty with directly improving these traits. However, seed infection and aflatoxin contamination had significant negative r G with drought tolerance traits, especially with pod yield (–0.29** to–0.93**) under drought conditions, indicating that genotype selection for drought tolerance could improve aflatoxin resistance. Moreover, r G were strong between seed infection and aflatoxin contamination with HI (–0.33** to–0.89**), SLA (0.50** to 0.92**) and SCMR (–0.60** to–0.83**). The results indicate that HI, SLA, or SCMR traits under long-term drought conditions could be used as indirect indicators of aflatoxin resistance. Because measurements for SLA and SCMR are simple, realizable and rapid, SLA and SCMR may be practical and cost effective for application in large scale breeding programs.

Variability of genotype and genotype x environment (G x E) interactions for fatty acids are important to develop high-oleic types in peanut varietal improvement programs. The objective of this study was to determine the variation in fatty acid composition among peanut genotypes and G x E interactions of fatty acids in three groups of genotypes with high, intermediate, and low-oleic acid. Twenty-one genotypes were tested in three environments consisting of two rainy seasons and one dry season. The results indicated that G x E interactions were significant for biomass, pod yield, and harvest index and also for oleic, linoleic acids, and O/L ratio. G x E interactions were less important than genotypic main effect. For oleic acid, significant interactions were found in the intermediate and low-oleic groups only. Therefore, selection for high-oleic trait in peanut breeding programs should be effective.

With 1 figure and 4 tables Abstract 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.

A large root system can be an important character for drought tolerance. Measuring root characteristics in soil medium is tedious, time consuming, and labor intensive. The objective of this study was to determine the association between root characteristics of peanut ( Arachis hypogaea L.) grown in hydroponics and in pot experiments. Twelve peanut genotypes were planted in a randomized complete block design with four replications in a hydroponics study, a small pot, and a large pot experiment. The studies were conducted in two years during 2004–2005. Shoot dry weight, root dry weight, root-to-shoot ratio, root length, root surface, average diameter of roots, and root volume were measured. Tifton-8 and ‘KK 60-3’ had consistently higher values for all root characteristics compared to the other genotypes. Root characteristics of peanut genotypes grown in hydroponics were positively correlated with those of peanut genotypes grown in pot conditions. The results suggested that assessment of root characteristics of peanut in hydroponics for possible drought tolerance could replace the assessment in soil medium conditions.

The current study investigates the association between drought tolerance traits and aflatoxin contamination in peanut grown under long-term drought. Two field experiments were conducted at Khon Kaen University, Thailand using a split–split plot design with three drought stress levels as main plots, 11 genotypes as sub-plots, and two soil inoculations of Aspergillus flavus treatments as sub-sub-plots. The effects of temperature, soil moisture and A. flavus population on kernel colonization and aflatoxin contamination, and drought tolerance traits viz. specific leaf area (SLA) and root length density (RLD) were measured. The results demonstrated that elevated soil temperatures and reduced soil moisture, favored aflatoxin production. Drought in combination with higher levels of A. flavus inoculum load in the soil resulted in an increase in the fungal populations in the soil which in turn resulted in increased kernel colonization and subsequent aflatoxin contamination. A combination of SLA and RLD, and kernel colonization had a significant influence on aflatoxin contamination under drought conditions in both seasons (r = 0.73** and 0.76**). The results revealed that drought tolerance traits (SLA and RLD) could be contributing to resistance to aflatoxin contamination suggesting that a combination of SLA, RLD and kernel colonization could be used as selection criteria in selecting parents for aflatoxin resistance.

Root characters have been well established as drought resistance traits in peanut. However, the relationships of root characters with transpiration efficiency (TE) have not been well understood. The objective of this study was to investigate the relationships between root traits and TE under early season drought. Two greenhouse experiments were conducted during February–May 2004 and November 2004–March 2005 at the Field Crop Research Station of Khon Kaen University, in Khon Kaen province of Thailand. A randomized complete block design (RCBD) was used with 2 factorial set-up with four replications. Factor A consisted of two water regimes, i.e. irrigated control (FC) and 1/3 available soil water (1/3 AW) from emergence to 40 days after emergence followed by adequate water supply, and factor B comprised of 11 peanut genotypes. Data were recorded for specific leaf area (SLA) and SPAD chlorophyll meter reading (SCMR) at 40 and 60 days after emergence (DAE) and TE and root dry weight (RDW) at harvest. Early season drought increased SCMR, TE and RDW but it reduced SLA. Strong and more consistent variation for TE were observed among 11 peanut genotypes across seasons. Across both seasons, ICGV 98300, KK 60-3 and Tifton-8 had high TE and also had large root systems under drought conditions. KK 60-3 and Tifton-8 had low SLA and high SCMR under early season drought conditions. Root dry weight had a contribution to TE under well-watered and drought conditions, especially under drought condition. SCMR and SLA had smaller contributions to TE under well-watered and ESD conditions. From this study it was apparent that root dry weight was an important trait for TE under early season drought.

The objectives of the present study were to investigate the variability in yield responses of peanut genotypes subjected to Early Season Drought (ESD) and to evaluate characters associated with yield. The field experiment was conducted in the rainy and dry seasons. Eleven genotypes of peanut and two water regimes (field capacity and 1/3 available soil water) were laid out in split plot design with four replications. Where, water regimes were assigned in main plots and 11 peanut genotypes were laid out in subplots. Imposition of ESD following re-watering resulted in an increase of pod yield compared to the irrigated treatment. Significant genotypic differences in yield response in relation to ESD were observed in this study and this could be useful in selecting desired genotypes in peanut breeding program. The highest pod yields were found in ICGV 98303 and Tainan 9 in the rainy season, whereas, in the dry season, ICGV 98303 was still highest for pod yield followed by ICGV 98300. After re-watering, SPAD chlorophyll meter reading, leaf area index and biomass productions were increased. Thus, increase in yield was associated with high biomass production after recovery combined with great green leaf area and concentration of leaf chlorophyll.

Drought is the major abiotic constraint affecting peanut productivity and quality worldwide. There is a pressing need to improve the water use efficiency (WUE) of rain-fed peanut production. Breeding varieties with higher water use efficiency is seen as providing part of the solution. The objectives of this work were to (i) evaluate genetic variation in WUE, harvest index, root dry weight, specific leaf area (SLA) and SPAD chlorophyll meter reading (SCMR) among peanut genotypes in response to different available soil water levels and (ii) assess the relevance of root dry weight, SLA and SCMR to WUE in peanut under receding soil moisture levels. Two greenhouse experiments were conducted in the dry and rainy seasons in 2002/2003. The 11 peanut genotypes (ICGV 98300, ICGV 98303, ICGV 98305, ICGV 98308, ICGV 98324, ICGV 98330, ICGV 98348, ICGV 98353, Tainan 9, KK 60-3 and Tifton-8) and three soil moisture levels [field capacity (FC), 2/3 available soil water (AW) and 1/3 AW] were laid out in a factorial randomized complete block design (RCBD) with six replications. At 37, 67, and 97 day after sowing (DAS), data were recorded for SLA and SCMR. Root dry weight, harvest index (HI) and WUE were recorded at harvest. Drought reduced WUE, root dry weight and HI. Across both seasons, Tifton-8 and ICGV 98300 had high WUE and also had large root systems under drought conditions. ICGV 98324 and Tifton-8 had low SLA and high SCMR under stressed and non-stressed condition. Under drought conditions, ICGV 98324 had high HI and Tifton-8 had low HI. Root dry weight had a greater contribution to WUE under well-watered and mild drought (2/3 AW). Under severe drought (1/3 AW), SLA showed a more important contribution to WUE than the other traits. Traits that were associated to high WUE under drought conditions were different among different peanut genotypes. ICGV 98300 maintained high root dry weight under 2/3 AW and ICGV 98324 maintained low SLA and high SCMR under 1/3 AW. Tifton-8 had both large root systems and low SLA associated with high WUE.

Drought stress reduces growth and yield in peanut (Arachis hypogaea L.) and also reduces nitrogen fixation (NF). Peanut production in drought prone areas should be enhanced by the development of cultivars that can fix more nitrogen (N) under drought conditions. The aims of this study were to estimate heritability for NF and to estimate phenotypic and genotypic correlations among traits related to NF with drought-resistance traits and yield under well-watered and drought conditions. A total of 140 lines in the F 4:7 and F4 :8 generations derived from four crosses, parental lines, and a non-nodulating line as a non-N 2 -fixing reference plant were evaluated in the dry seasons 2005/2006 and 2006/2007. These lines were evaluated in rhizobium inoculated soil without N fertilizer under field capacity (FC) and 2/3 available soil water (AW). Data were recorded for specific leaf area (SLA), SPAD chlorophyll meter reading (SCMR), nodule number (NN), nodule dry weight (NDW), shoot dry weight (SDW), pod dry weight (PDW), total dry weight (TDW), harvest index (HI), and NF. Broad-sense heritability (h 2 b ) and narrow-sense heritability (h 2 n ) estimates for NF under FC and 2/3 AW were in the same ranges (h 2 b = 0.84 to 0.98 and h 2 n = 0.29 to 0.39). Positive relationships between NF under FC and 2/3 AW (r = 0.73, P≤ 0.01) indicated that selection for the lines that fixed high N under well-watered conditions should produce lines that fixed high N under drought conditions. Selection for NF under drought conditions might be more effective in improving yield because of a higher correlation between NF and PDW (r G = 0.43, P ≤ 0.01) under drought conditions than under FC (r G = 0.13). The use of SCMR and SLA as surrogate traits for NF would be less effective than direct selection because of weak correlations between these traits and NF.

A major limitation of the application of a crop simulation model is the determination of cultivar coefficients, as the recommended procedure requires extensive data sampling throughout the growing season which is very impractical when a large number of lines are involved or when critical resources are limited. Our previous study has shown that a reduced set of experimental data can be used to accurately estimate the cultivar coefficients of peanut lines as used by the CSM-CROPGRO-Peanut model. The objectives of this study were to verify our previous finding and to evaluate the derived cultivar coefficients in assisting multi-environment evaluation of peanut lines with the CSM-CROPGRO-Peanut model. Nine peanut lines in a regional yield trial (Set I) and ten peanut lines in a standard yield trial (Set II) were grown during the dry and rainy seasons of 2005. Data were collected on plant growth and development following the optimum protocol from our previous study. These data were used for model calibration to derive the cultivar coefficients of the individual peanut lines. Model calibration showed simulated values of phenology and growth characteristics of the peanut lines that were close to the corresponding observed values, with the coefficient of determination (r2) and the index of agreement (d) close to optimal values of 1, and a normalized root mean square error (RMSEn) smaller than 35%. Genetic variation among lines in cultivar coefficients was also observed. The initial model evaluation with data collected in the 2004 rainy season confirmed that model prediction was good for independent data, i.e., giving high values of r2 and d; and small RMSEn. The derived cultivar coefficients were shown to enable the CSM-CROPGRO-Peanut model to satisfactorily mimic yield ranking and stability of peanut lines in the Set I and Set II yield trials with 10 and 8 environments, respectively. Among the top five highest yielding lines based on mean observed pod yield (upper 56% for the Set I yield trial and upper 50% for the Set II yield trial), four lines were identified by model simulation in both sets. Also, the same top yielding lines in the two sets were identified by both simulation and experimentation. The model predicted similar GGE biplot patterns as present in observed trials, and also identified the same stable lines as the observed data. It is concluded that a reduced set of field data can be used for model application in assisting the multi-environment evaluation of peanut lines.

Groundnut as a pre-rice crop is usually harvested 1–2 months before rice transplanting. During this lag phase much of N in groundnut residues could be lost due to rapid N mineralization. Mixing of abundantly available rice straw with groundnut residues may be a means for reducing N and improve subsequent crop yields. The objectives of this experiment were to investigate the effect of mixing groundnut residues and rice straw in different proportions on (a) growth and yield of succeeding rice, (b) groundnut residue N use efficiency and (c) N lost ( 15 N balance) from the plant–soil system and fate of residue N in soil fractions. The experiment consisted of six treatments: (i) control (no residues), (ii) NPK (at recommended rate, 38 kg N ha −1 ), (iii) groundnut residues 5 Mg ha −1 (120 kg N ha −1 ), (iv) rice straw 5 Mg ha −1 (25 kg N ha −1 ), (v) 1:0.5 mixed (groundnut residues 5 Mg: rice straw 2.5 Mg ha −1 ), and (vi) 1:1 mixed (groundnut residues 5 Mg: rice straw 5 Mg ha −1 ). After rice transplanting, samples of the lowland rice cultivar KDML 105 were periodically collected to determine growth and nutrient uptake. At final harvest, dry weight, nutrient contents and 15 N recovery of labeled groundnut residues were evaluated. Significant effects of residue management treatments on rice growth and nutrient uptake dynamics were observed from 30 days after transplanting onwards. At final harvest, the highest grain yield and N content of rice were obtained in the 1:1 (3.7 Mg ha −1 ) and 1:0.5 mixed treatments followed by sole groundnut residues > rice straw > NPK > control (2.8 Mg ha −1 ) treatments. There was a significant relationship between mineral N content in soil before transplanting and rice yield at harvest. Mixed residue treatments had significantly ( p 15 N recoveries (13%) in rice than in the sole groundnut treatment (10%) but they were lower than the recovery of labeled mineral N fertilizer in the NPK treatment (29%). The highest 15 N recoveries in all treatments were observed in the topsoil (0–15 cm) where over 80% of 15 N was located. Systems N unaccounted for from groundnut residues (32%) were similar to fertilizer N losses (30%), but they were lowest in the 1:0.5 mixed treatment (15%). The highest δ 13 C value occurred in residue treatments and 13 C was positively related to N uptake while negatively related to internal N use efficiency. The result from our study demonstrated that mixing groundnut residues and rice straw could delay N release during the pre-rice lag phase leading to an improved synchrony in N demand/supply and increased growth and yield of the succeeding rice and reduced N losses from the soil–plant system.

Efficient testing of crop breeding lines requires a set of complementary test sites that adequately sample the target environments with minimal duplication. Such test sites have been derived from actual multi-environmental trial (MET) data, which often have a limitation with respect to their environmental coverage. However, this limitation can be overcome using a crop simulation model. The goal of this study was to determine the efficient test sites for METs of peanut breeding lines in Thailand using the CSM-CROPGRO-Peanut model. The model was used to simulate pod yield for 17 peanut lines at all peanut production areas in Thailand that included 76 locations in the early-rainy season, 39 locations in the mid-rainy season and 47 locations in the dry season for 30 years. The simulated data were used to sub-divide the locations for each season into groups using cluster analysis and the genotype plus genotype × environment (GGE) biplot method. Six sets of test sites were obtained based on different scenarios for site selection that included combinations of geographical distribution and representation of location-groups as determined by the two methods. Set 1 was based on geographic distribution. Sets 2–4 were based on location grouping by cluster analysis, but with the sites distributed in all regions (Set 2), or only in the north (Set 3) or northeast (Set 4). Set 5 consisted of the sites currently used, and Set 6 was based on location grouping by the GGE biplot. Although Sets 2 and 6 appeared to capture more genotype × location interaction than the others, performance rankings of the test genotypes were almost the same for all sets. They were, therefore, considered equally effective for breeding line evaluation. The final selection was then based on the convenience, and consequently the cost, for conducting the METs. Set 4 was considered most preferable in this regard. This study demonstrated the usefulness of a crop simulation model as a tool in determining the most efficient test sites for the evaluation of peanut breeding lines.

The aim of this study was to investigate whether some root characters and physiological characters are related to drought resistance in some elite germplasm lines earlier identified as drought resistant based on pod yield. Four peanut genotypes were tested in a pot experiment under two soil moisture levels [Field Capacity (FC) and 1/3 available water (1/3 AW)]. A 2x4 factorial experiment was laid out in RCBD with six replications. Data were recorded for Relative Water Content (RWC), Specific Leaf Area (SLA), SPAD Chlorophyll Meter Reading (SCMR), root and biomass at 70 days after planting. Root characters, biomass production, pod yield and Harvest Index (HI) were recorded at harvest and Drought Tolerance Index (DTI) for these traits were also calculated. Differences between water treatments were also significant for RWC, SLA, Root Dry Weight (RDW) and biomass but not significant for SCMR, harvest index and pod yield. Drought stress reduced RWC, SLA, RDW and biomass but had no significant effect on SCMR, harvest index and pod yield. Significant differences among peanut genotypes were found for SLA at both water treatments. ICGV 98353 had the lowest SLA at both water treatments. Peanut genotypes were significantly different for RDW and RWC at 1/3 AW only. KK 4 had the highest RDW. ICGV 98324 performed best for RWC and it also had the highest DTI for RWC. ICGV 98324 also had the highest SCMR, which was significantly different among peanut genotypes at FC

The number of pods per unit area is an important component of pod yield of peanut. The goals of this study were to determine the relationships of (i) pod yield with number of pods per unit area and weight per pod and (ii) number of pods per unit area with crop growth rate (CGR) and duration during the different developmental stages. Fifteen peanut lines were tested at Khon Kaen University in Northeast Thailand during the 2002 and 2003 rainy and the 2003 and 2004 dry seasons. Data were recorded on developmental stages, biomass, pod yield, and yield components. The CGRs were calculated for different developmental periods. Results showed a positive linear relationship between pod yield and number of pods per unit area across genotypes and seasons (R 2 = 0.69; P > F F = 0.85). A significant relationship between number of pods per unit area and CGR among the test genotypes was found only during the period from R6 to R7 (R 2 = 0.44; P > F = 0.007), and the same relationship across seasons was significant (R 2 = 0.45; P > F < 0.001) only during the period from planting to R4. These results indicate that number of pods per unit area is the major determinant for pod-yield differences among peanut lines, and that the differences among lines for this trait are influenced by CGR during the period from R6 to R7.

Inheritance of traits is important for developing effective breeding schemes for improving desired traits. The aims of this study were to estimate the heritabilities (h 2 ) of drought resistance traits and the genotypic (r G ) and phenotypic (r P ) correlations between drought resistance traits and agronomic traits, and to examine the relationships between drought resistance traits under stressed and nonstressed conditions. The 140 lines in the F 4:7 and F 4:8 generations from four peanut (Arachis hypogaea L.) crosses were tested under fi eld capacity (FC) and twothirds available soil water (2/3 AW) in two fi eld experiments. Data were recorded for specifi c leaf area (SLA), SPAD chlorophyll meter reading (SCMR), and biomass, pod yield, harvest index, number of mature pods per plant, seed per pod, and seed size. The h 2 for biomass, pod yield, DTI (drought tolerance index) (pod yield), DTI (biomass), HI, SLA, and SCMR were high for all tested crosses (0.54–0.98). The r G (−0.61 and −0.66) and r P (−0.61 and −0.66) between SLA and SCMR were strong and negative under 2/3 AW and FC. Under 2/3 AW conditions, SCMR was positively correlated with pod yield and seed size. Compared to SLA, SCMR had higher r G and r P with pod yield, biomass, and other agronomics traits. Signifi cant correlations between FC and 2/3 AW conditions were found for pod yield, biomass, SCMR, and SLA, indicating that these traits could be selected under FC or 2/3 AW conditions. SPAD chlorophyll meter reading, which is easy to measure, is potentially useful as a selection trait for drought resistance because of high h 2 and positive correlation with pod yield and agronomic traits.

Groundnut as a pre-rice crop is usually harvested 1-2 months before rice transplanting, during which much of legume residue N released could be lost. Our objectives were to investigate the effect of mixing groundnut residues (GN, 5 Mg ha -1 ) with rice straw (RS) in different proportions on: (i) regulating N dynamics, (ii) potential microbial interactions during decomposition, and (iii) associated nitrous oxide and methane emissions at weekly intervals during the lag phase until rice transplanting (i, ii) or harvest (iii). Decomposition was fastest in groundnut residues (64% N lost) with a negative interaction for N loss when mixed 1:1 with rice straw. Adding groundnut residues increased mineral N initially, while added rice straw led to initial microbial N immobilization. Mineral N in mixed residue treatments was significantly greatest at the beginning of rice transplanting. Soil microbial N and apparent efficiency were higher, while absolute and relative microbial C were often lowest in groundnut and mixed treatments. Microbial C:N ratio increased with increasing proportion of added rice straw. N 2 O losses were largest in the groundnut treatment (12.2 mg N 2 O-N m -2 day -1 ) in the first week after residue incorporation and reduced by adding rice straw. N 2 O-N emissions till rice harvest amounted to 0.73 g N 2 O-N m -2 in the groundnut treatment. CH 4 emissions were largest in mixed treatments (e.g. 155.9 g CH 4 m -2 , 1:1 treatment). Mixing residues resulted in a significant interaction in that observed gaseous losses were greater than predicted from a purely additive effect. It appears possible to regulate N dynamics by mixing rice straw with groundnut residues; however, at a trade-off of increased CH 4 emissions.

Coefficients of crop cultivars, a required input for the application of crop simulation models, are normally derived from experiments designed specifically for their estimation. This procedure is laborious and time consuming even with a reduced data set. Recent studies have shown that cultivar coefficients for soybean lines can be derived from standard crop performance trials. However, this needs to be confirmed in other crops and be simplified for broader applications. The objective of this study was to determine the feasibility of estimating cultivar coefficients for new peanut lines using data from standard performance trials. Data from performance trials of 17 peanut lines that were conducted in farmers’ fields and research stations in the northeastern and northern regions of Thailand during 2002–2004, totaling eight environments, were used in this study. The data that were collected included dates of first flower and harvest maturity, final biomass, pod and seed yield, seed size, pod and seed harvest index, and shelling percentage. These data were used for the calculation of the cultivar coefficients using the Genotype Coefficient Calculator (GENCALC) program, which is part of the Decision Support System for Agrotechnology Transfer (DSSAT). Evaluation of the derived cultivar coefficients was conducted with time series growth data collected in three additional experiments grown during the 2002 rainy, 2003 dry, and 2004 dry seasons. The model calibration with GENCALC resulted in cultivar coefficients that produced simulated values for the development and growth characteristics that were close to their corresponding observed values, with root mean square errors (RMSE) ranging from 1.5 to 4.1 days for development traits and 0.20–1.32 t ha � 1 for growth traits and coefficient of determinations (r 2 ) ranging from 0.55 to 0.97 for all traits. The evaluation of the cultivar coefficients that were derived from the performance trials data with independent data worked well for all development traits and fairly well for the plant growth characteristics, as judged by RMSE, r 2 , normalized root mean square error (RMSEn) and index of agreement (d). The mean RMSE values for days to first flower and to harvest maturity were 1.6 and 2.4 days; and mean r 2 were 0.72 and 0.91, respectively. The mean RMSEn values calculated from time series growth data were 17.9, 24.6 and 11.5% with the mean d values of 0.88, 0.93 and 0.93 for the 2002 rainy, 2003 dry and 2004 dry seasons, respectively. It is concluded that the cultivar coefficients of peanut lines can be estimated from typical data that are collected in standard performance trials using either GENCALC or similar methodologies.