Heritability of,and genotypic correlations between,aflatoxin traits and physiological traits for drought tolerance under end of season drought in peanut (Arachis hypogaea L.)

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 (r_G) and phenotypic (r_P) correlations between drought resistance traits and aflatoxin traits in peanut. One hundred-forty peanut lines in the F_4:6 and F_4:7 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 (r_P = −0.25** to 0.32**, r_G = −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 (r_P = 0.13** to 0.46**, r_G = 0.26** to 0.81**). SCMR was negatively correlated with aflatoxin traits (r_P = −0.10** to −0.40**, r_G = −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.     

Moisture-deficit-induced changes in leaf-water content,leaf carbon exchange rate and biomass production in groundnut cultivars differing in specific leaf area

Field experiments were conducted during two rainy seasons to study the effect of soil moisture deficit on total biomass, pod yield, harvest index (HI) and drought tolerance index (DTI) in groundnut (Arachis hypogaea L.) cultivars possessing a wide range of specific leaf area (SLA, 144–241 cm² g⁻¹). There were three soil moisture regimes: adequate irrigation (W₁), drought simulated under rain-out-shelter (W₂) and rain-fed (W₃). This experiment had two parts, in one, five cultivars were exposed to W₁, W₂ and W₃, and in a second, seven cultivars were exposed to W₁ and W₃. Using the same set of seven cultivars, pot-culture experiments were conducted to study relative water content (RWC), stomatal conductance (g_s) and single leaf carbon exchange rate (CER) during increasing moisture-deficit in two contrasting (rainy and summer) seasons. Variation in DTI was significant, and low SLA types had greater DTI under both W₂ and W₃. The ranking of SLA among cultivars was consistent between experiments conducted during the two seasons. The rate of reduction in leaf RWC during the progressive moisture-deficit was related directly to SLA (r=0.78, P<0.01). The coefficient of determination of the slopes calculated between RWC and soil moisture during the experimental period was more in the summer (r²=0.82) than the rainy (r²=0.54) season.Under increasing moisture-deficit, the low SLA types were able to maintain higher RWC, CER and g_s in both seasons. The relationships between RWC and CER (r=0.91, P<0.01), and RWC and g_s (r=0.65, P<0.01) were significant.It is suggested that under water-limited conditions there is a significant inverse relationship between SLA and RWC. The low SLA types (water use efficient) were found to be drought tolerant in terms of total dry matter production in the field studies, and maintenance of higher RWC under drought like situations in pot-culture experiments. Thus the ability of the low SLA types (higher water use efficiency, WUE) to maintain higher RWC may form the basis for the differences in drought tolerance vis a vis WUE in groundnut cultivars differing in SLA. Suggestions are made to select parents for drought tolerance or WUE, and to initiate breeding to combine traits like high HI, and WUE in terms of lower SLA. Ultimately, selection for both WUE (measured in terms of SLA) and yield traits (HI) should result in cultivars with improved performance in rain-fed agriculture.     

Genetic gains in grain yield, net photosynthesis and stomatal conductance achieved in Henan Province of China between 1981 and 2008

Knowledge of the changes in agronomic and photosynthetic traits associated with genetic gains in grain yield potential is essential for an improved understanding of yield-limiting factors and for determining future breeding strategies. The objectives of this study were to identify agronomic and photosynthetic traits associated with genetic gains in grain yield of facultative wheat (Triticum aestivum L.) between 1981 and 2008 in Henan Province, the most important wheat producing area in China. During the 2006-2007 and 2007-2008 crop seasons, a yield potential trial comprising 18 leading and new cultivars released between 1981 and 2008 was conducted at two locations, using a completely randomised block design of three replicates. Results showed that average annual genetic gain in grain yield was 0.60% or 51.30 kg ha⁻¹ yr⁻¹, and the significant genetic improvement in grain yield was directly attributed to increased thousand grain weight which also contributed to the significant increase in harvest index. The genetic gains in rates of net photosynthesis at 10, 20 and 30 days after anthesis were 1.10% (R² = 0.46, P < 0.01), 0.68% (R² = 0.31, P < 0.05) and 6.77% (R² = 0.34, P < 0.05), respectively. The rates of net photosynthesis at 10 (r = 0.58, P < 0.05), 20 (r = 0.59, P < 0.05) and 30 (r = 0.65, P < 0.01) days after anthesis were closely and positively correlated with grain yield. A slight decrease in leaf temperature and an increase in stomatal conductance after anthesis were also observed. Grain yield was closely and positively associated with stomatal conductance (r = 0.69, P < 0.01) and transpiration rate (r = 0.63, P < 0.01) at 30 days after anthesis. Therefore, improvement of those traits was the likely basis of increasing grain yield in Henan Province between 1981 and 2008. The genetic improvement in yield was primarily attributed to the utilization of two elite parents Yumai 2 and Zhou 8425B. The future challenge of wheat breeding in this region is to maintain the genetic gain in grain yield and to improve grain quality, without increasing inputs for the wheat-maize double cropping system.     

Association between aflatoxin contamination and drought tolerance traits in peanut

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.     

Environmental effects on seed yield determination of irrigated peanut crops: Links with radiation use efficiency and crop growth rate

In Argentina, delayed sowing causes a decrease in seed yield and in radiation use efficiency (RUE) of peanut crops (Arachis hypogaea L.), but it is not known if RUE reduction is mainly due to reduced temperature during late reproductive stages or to a sink limitation promoted by decreased seed number in these conditions. We analyzed seed yield determination and RUE dynamics of two cultivars (Florman and ASEM) in four irrigated field experiments (Exp_n) grown at three sites and five contrasting sowing dates (between 17 October and 21 December) in three growing seasons. An additional field experiment was performed with widely spaced plants (i.e. with no interference among them) to evaluate the effect of peg removal on RUE and leaf carbon exchange rate (CER). Seasonal dynamics of mean air temperature and irradiance, biomass production (total and pods), and intercepted photosynthetically active radiation (IPAR) were followed. Seed yield and seed yield components (pod number, seeds per pod, seed number and seed weight) were determined at final harvest. Crop growth rate (CGR) and pod growth rate (PGR) were computed for growth phases of interest. RUE values for crops sown until 14 November were 1.89–1.98 g MJ⁻¹ IPAR, within the usual range. RUE decreased significantly for cv. Florman in the late sowing of Exp₁ (29 November) and for both cultivars in Exp₃ (21 December sowing). Across experiments, seed yield (4.5-fold variation relative to minimum) was strongly associated (r² = 0.87, P < 0.0001) with variations in seed number (3.5-fold variation relative to minimum), and to a lesser extent (r² ≤ 0.54, P ≤ 0.001) to variations in seed weight (1.9-fold variation relative to minimum). Seed number was positively related (P < 0.01) to CGR (r² = 0.66) and to PGR (r² = 0.72) during the R₃–R_6.5 phase (seed number determination window), while crop growth during the grain-filling phase (i.e. between R_6.5 and final harvest) was positively associated with grain number (r² = 0.80, P < 0.001). No association was found between RUE and mean air temperature, neither for the whole cycle nor for the phase between R_6.5 and final harvest, which showed the largest temperature variation (16.4–22.4 °C) across experiments. Use of mean minimum temperature records (range between 13.8 and 18.5 °C) did no improve the relationship. However, grain-filling phase RUE showed a positive (r² = 0.69, P = 0.003) linear response to seed number across experiments. This apparent sink limitation of source activity was consistent with the reduced RUE (from 2.73 to 1.42 g MJ⁻¹ IPAR) and reduced leaf CER at high irradiance (from ca. 30 to 15 μmol m⁻² s⁻¹) for plants subjected to 75% peg removal.     

Kernel number determination differs among maize hybrids in response to nitrogen

In maize, the effects of nitrogen (N) deficiencies on the determination of kernel number per plant (KNP) have been described only by changes in plant growth rate during the critical period for kernel set (PGRcp). We hypothesize that N availability affects KNP also through variations in biomass allocation to the ear, which determines a stable N concentration in this organ. Six maize hybrids of different breeding origin were evaluated in field experiments at two N levels (0 and 400 kg N ha⁻¹ applied). Traits included were KNP and per apical ear (KN_E1), and the allometric estimation of PGRcp, ear growth rate during the critical period (EGRcp), and N content and N concentration in different plant organs. We demonstrated that (i) N availability promoted differences among genotypes (G) in the response of EGRcp and KNP to PGRcp, (ii) variations in KN_E1 were explained by EGRcp (r² = 0.64) and by ear N content at silking + 12 d (r² = 0.64), and (iii) ear N concentration was a highly conservative trait (range between 10.47 and 15.98 mg N g biomass⁻¹) as compared to N concentration in vegetative tissues (range between 4.94 and 18.04 mg N g biomass⁻¹). Three response patterns were detected among hybrids, one for which the relationship between EGRcp and PGRcp did not vary between N levels and experiments, a second one for which N availability affected this relationship, and a third one for which the response was affected by the year (Y) effect. These results, together with the high correlation between EGRcp and ear N content (r² = 0.88), evidenced the importance of both photo-assimilate and N availability on EGRcp and KNP determination. Values of 1.5–2.3 g ear⁻¹ d⁻¹ during the critical period and 0.49–0.70 g of N ear⁻¹ at silking + 12 d were determined as thresholds for maximizing KN_E1, and both could be easily estimated by means of allometric models.     

Field-based evaluation of vernalization requirement,photoperiod response and earliness per se in bread wheat (Triticum aestivum L.)

Vernalization requirement, photoperiod response and earliness per se (EPS) of bread wheat cultivars are often determined using controlled environments. However, use of non-field conditions may reduce the applicability of results for predicting field performance as well as increase the cost of evaluations. This research was undertaken, therefore, to determine whether field experiments could replace controlled environment studies and provide accurate characterization of these three traits among winter wheat cultivars. Twenty-six cultivars were evaluated under field conditions using two natural photoperiod regimes (from different transplanting dates) and vernalization pre-treatments. Relative responses to vernalization (RRV_GDD) and photoperiod (RRP_GDD) were quantified using the reciprocal of thermal time to end of ear emergence, whereas earliness per se was estimated by calculating thermal time from seedling emergence until end of ear emergence for fully vernalized and lately planted material. An additional index based on final leaf numbers was also calculated to characterize response to vernalization (RRV_FLN). To test whether the obtained indices have predictive power, results were compared with cultivar parameters estimated for the CSM-Cropsim-CERES-Wheat model Version 4.0.2.0. For vernalization requirement, RRV_GDD was compared with the vernalization parameter P1V, for photoperiod (RRP_GDD), with P1D, and for earliness per se, EPS was compared with the sum of the component phase durations. Allowing for variation in EPS in the calibration improved the relation between observed versus simulated data substantially: correlations of RRP_GDD with P1D increased from r² = .34 (p < .01), to .82 (p < .001), and of RRV_GDD with P1V, from r² = .88 (p < .001), to .94 (p < .001). In comparisons of observed versus simulated anthesis dates for independent field experiments, the estimated model coefficients resulted in an r² of .98 (p < .001) and root mean square error of 1d. Overall, the results indicated that combining planting dates with vernalization pre-treatments can permit reliable, quantitative characterization of vernalization requirement, photoperiod response and EPS of wheat cultivars. Furthermore, emphasize the need for further study to clarify aspects that determine EPS, including whether measured EPS varies with temperature or other factors.     

Characterizing leaf gas exchange responses of cotton to full and limited irrigation conditions

Plant responses to water deficit need to be monitored for producing a profitable crop as water deficit is a major constraint on crop yield. The objective of this study was to evaluate physiological responses of cotton (Gossypium hirsutum) to various environmental conditions under limited water availability using commercially available varieties grown in South Texas. Soil moisture and variables of leaf gas exchange were measured to monitor water deficit for various varieties under different irrigation treatments. Lint yield and growth variables were also measured and correlations among growth parameters of interest were investigated. Significant differences were found in soil moisture, leaf net assimilation (A_n), stomatal conductance (g), transpiration rate (T_r), and instantaneous water use efficiency (WUE_i) among irrigation treatments in 2006 while no significant differences were found in these parameters in 2007. Some leaf gas exchange parameters, e.g., T_r, and leaf temperature (T_L) have strong correlations with A_n and g. A_n and WUE were increased by 30–35% and 30–40%, respectively, at 600 μmol (CO₂) m⁻² s⁻¹ in comparison with 400 μmol (CO₂) m⁻² s⁻¹. Lint yield was strongly correlated with g, T_r, WUE, and soil moisture at 60 cm depth. Relative A_n, T_r, and T_L started to decrease from FTSW 0.3 at 60 cm and FTSW 0.2 at 40 cm. The results demonstrate that plant water status under limited irrigation management can be qualitatively monitored using the measures of soil moisture as well as leaf gas exchange, which in turn can be useful for describing yield reduction due to water deficit. We found that using normalized A_n, T_r, and T_L is feasible to quantify plant water deficit.     

Mixing groundnut residues and rice straw to improve rice yield and N use efficiency

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 (¹⁵N 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 ¹⁵N recovery of labeled groundnut residues were evaluated.     

The Rht13 dwarfing gene reduces peduncle length and plant height to increase grain number and yield of wheat

The green-revolution Rht-B1b and Rht-D1b dwarfing alleles are usually associated with increased wheat yields but are linked to reduced early growth and poor emergence if sowing conditions are unfavourable. Other dwarfing genes are available but not used in commercial breeding. The Rht13 bread wheat donor, Magnif M1, produces uniquely short peduncle and penultimate internodes to reduce plant height. A set of near-isogenic (NILs) and recombinant inbred (RILs) lines varying for height were developed from the cross of Magnif M1 and the Rht8c-containing Chuan-mai 18, and evaluated for a range of agronomic characteristics across favourable environments. Reductions in plant height were associated with increased grain number (r² = 0.35**) and harvest index (r² = 0.62**) in the NILs. Reduced-height RILs containing the Rht13-linked, Xgwm577_M microsatellite marker were significantly shorter, produced greater biomass, yield and harvest index, and increased spike and grain number than lines without the marker. Approximately 74 and 7% of the total phenotypic variance in plant height was accounted for by allelic differences in Xgwm577 and Rht8 loci, respectively. The peduncle and penultimate peduncle internodes of Rht13-containing lines were proportionately shorter than Rht8c-containing sibs and lines containing the Rht-B1b dwarfing allele. The unique height-reducing phenotype, increased grain number and yield associated with Rht13 indicate considerable potential for use of this dwarfing allele for improving wheat performance.     

Chitin-based bioformulation of Beauveria bassiana and Pseudomonas fluorescens for improved control of leafminer and collar rot in groundnut

The talc-based formulation of Beauveria bassiana (B2 and B4) and Pseudomonas fluorescens (TDK1 and Pf1) strains and its mixture amended with and without chitin were developed and tested for their efficacy against the leafminer insect pest (Aproaerema modicella) and collar rot (or) seedling blight pathogen (Sclerotium rolfsii) in groundnut under glasshouse and field conditions. Application of talc-based formulation of B2 + TDK1 + Pf1 strains mixture (amended with or without chitin) through seed, soil and foliar spray effectively reduced the incidence of leafminer and collar rot in groundnut compared to individual bioformulation and control treatments both under glasshouse and field conditions. Groundnut leaves when treated with this bioformulation mixture, altered the feeding behavior of leafminer larvae and increased larval mortality under in vitro. Further, a significant increase in growth parameters and yield were observed in groundnut plants treated with B2 + TDK1 + Pf1 compared to individual bioformulation and untreated control. Increased accumulation of chitinase enzyme was observed in groundnut plants treated with mixture of B2 + TDK1 + Pf1 against A. modicella and S. rolfsii when compared to other treatments.     

Effect of N supply on stalk quality in maize hybrids

The identification of maize nitrogen (N) response for stalk quality is valuable in stalk breeding improvement, stalk lodging resistance and for use in bioenergy. This study analyzed the effect of two N levels and estimated quantitative genetic parameters for stalk quality in summer maize in the north China plain (NCP). Thirty hybrids were sampled and tested from three to four geographic locations under high nitrogen (HN) (225 kg N ha⁻¹) and low nitrogen (LN) (0 kg N ha⁻¹) during 2006–2008. Compared to HN level, stalk crude protein (CP) was significantly reduced (22.06%) under LN level. Ether extract (EE), ash content (AC), in vitro dry matter digestion (IVDMD) and lignin content (LC) were lower under LN level. Cellulose content (CC), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were increased with a reduction in N, however N did not significantly affect EE, ADF and LC. An increase in NDF and ADF content under low vs. high N level was mainly attributed to a reduction in CC. ADF and NDF exhibited positive correlation and both showed a positive correlation with CC but a negative correlation with LC, IVDMD and CP. Negative correlations between IVDMD and CC, IVDMD and LC, and CP and CC were also detected. The interaction variance of genotype × year × location (σ²_GYL) for each N level, with the exception of σ²_GYL for CC under HN, was significant and most stalk quality traits were evaluated in different locations and years. The estimates of genetic variance (σ²_G) and heritability (h²) were greater under HN, with the exception of LC and EE. The interaction of genotype × nitrogen (σ²_GN) for CP was more important than σ²_G. The genotypic correlation coefficients (r_G) for performance in different stalk quality traits between HN and LN were significant. However, it was necessary to evaluate both HN and LN for IVDMD. For other stalk quality traits, breeding maize under HN levels may serve to develop hybrids well adapted to high and/or low N level. The response to N trend was similar between high oil and normal maize hybrids.     

Temporal dynamics of light and nitrogen vertical distributions in canopies of sunflower, kenaf and cynara

To enhance eco-physiological and modelling studies, we quantified vertical distributions of light and nitrogen in canopies of three Mediterranean bio-energy crops: sunflower (Helianthus annuus), kenaf (Hibiscus cannabinus) and cynara (Cynara cardunculus). Field crops were grown with and without water stress in 2008 and 2009. Canopy vertical distributions of leaf area index (LAI), photosynthetically active radiation (PAR), specific leaf area (SLA), nitrogen concentration (N_conc) and specific leaf nitrogen (SLN) were assessed over time for each crop × year × water input combination. Light and nitrogen distributions were quantified by the Beer's law (exponential model) and extinction coefficients for light (K_L) and nitrogen (K_N) were calculated. Within a year, K_L did not change significantly over the studied period in all irrigated crops, but differences in K_L were significant between years (sunflower: 0.74 vs. 0.89; kenaf: 0.62 vs. 0.71; cynara: 0.77). K_L estimates were always lower (−48 to −65%) in water-stressed sunflower and kenaf crops because of the reduction in leaf angle. These results should be taken into account, when simulating water-limited biomass production. Vertical SLN distributions were found in canopies when LAI was >1.5 (40 from 51 cases). These distributions were significantly correlated with the cumulative LAI from the top (r² = 0.75-0.81; P < 0.05), providing parameters to upscale photosynthesis from leaf to canopy levels. Vertical SLN distributions followed species-specific patterns over the crop cycle and varied less compared to PAR distributions between years. Lastly, we observed strong associations between SLN and PAR distributions in irrigated sunflower and kenaf canopies (r² > 0.66; P < 0.001). However, observed SLN distributions were less steep than the distributions that would maximize canopy photosynthesis.     

Impact of intercropping of medicinal and aromatic plants with organic farming approach on resource use efficiency in arecanut (Areca catechu L.) plantation in India

The present investigation was conducted at Vittal, Karnataka, India during 2004-2007 to study the feasibility of intercropping of medicinal and aromatic plants (MAPs) in arecanut plantation. The results revealed that MAPs can be successfully grown as intercrops in arecanut plantation with increased productivity and net income per unit area. Kernel equivalent yield of MAPs varied between 272 kg ha⁻¹ in case of Piper longum to 1218 kg ha⁻¹ in Cymbopogon flexuosus. Pooled data indicated that Asparagus racemosus produced fresh root yield of 10,666 kg ha⁻¹ of arecanut plantation and contributed to maximum kernel equivalent yield of 1524 kg ha⁻¹ among all medicinal and aromatic plants. Intercropping of MAPs in arecanut was found economical. The net return per rupee investment was highest in C. flexuosus (4.25) followed by Bacopa monnieri (3.64), Ocimum basilicum (3.46) and Artemisia pallens (3.12). The total system productivity of arecanut + MAPs intercropping system varied from 2990 to 4144 kg ha⁻¹. Arecanut + O. basilicum intercropping system registered significantly higher production efficiency 8.2 kg ha⁻¹ day⁻¹ than other systems. Intercropping of MAPs had more positive effect on soil pH in arecanut based cropping system. The soil pH was 5.6 in 2004 and it was 0.3-0.9 units higher in 2007. Soil organic carbon (SOC) content varied significantly due to intercropping of MAPs at the end of experiment. The SOC content increased in Aloe vera, A. pallens, P. longum and B. monnieri, while it depleted in grasses and rhizomatic MAPs. Based on demand and marketing opportunities for MAPs, farmers are advised to grow aromatic plants in large areas on a community basis to meet huge industrial demand and variety of medicinal crops in small areas to meet the requirement of traditional systems of medicine.     

Carpel weight, grain length and stabilized grain water content are physiological drivers of grain weight determination of wheat

Among the yield components, grain weight is considered a conservative trait whose determination is still beyond our complete understanding. Crop physiology uses a whole approach to study this complex trait, which can provide helpful information to plant breeders and molecular biologists. This study emphasizes the understanding of pre- and post-anthesis determinants of final grain weight. A field experiment was carried out in two growing seasons evaluating two wheat cultivars contrasting in grain weight potential. Carpel weight at pollination, grain dimensions, grain water, dry matter and volume dynamics were assessed. Among grain dimensions, grain length was the trait, which explained final grain weight (r² = 0.78; P < 0.01 and r² = 0.94; P < 0.001 for the 1st and 2nd season, respectively) and it was the first trait to stabilize after anthesis. Water content of grains stabilized little later and also showed a strong association with final grain weight (r² = 0.93; P < 0.01 and r² = 0.98; P < 0.01 for the 1st and 2nd season respectively). Most importantly, carpel weight at pollination showed a positive and linear association with final grain weight (r² = 0.79, P < 0.01 and r² = 0.86 P < 0.01 for the 1st and 2nd season, respectively) irrespective of the cultivar and grain position. In addition, positive associations were also found between grain volume, water content, grain length, and carpel weight at pollination. Therefore, the associations between pre- and post-anthesis traits found in this study support the hypothesis that grain weight is determined before anthesis and fruit tissues (i.e., pericarp in cereals and sunflower) set an upper limit to grain weight.     

Variability of light interception and radiation use efficiency in maize and soybean

Variability of light interception and its derivatives are poorly understood at the field-scale in maize (Zea mays L.) and soybean [Glyine max (L.) Merr.]. Quantifying variability can provide reliable estimates of field-scale processes and reliable methodology. A field study was conducted during the 2005 growing season in a 31 ha maize and 23 ha soybean field rotated annually near Ames, IA to measure variability of cumulatively intercepted photosynthetically active radiation (CI-PAR) and radiation use efficiency (RUE) by deploying eight line quantum sensors in each field. Cumulative mean PAR interception for soybean was 575 MJ m⁻² ending on day of the year (DOY) 249 compared with 687 MJ m⁻² in maize ending on DOY 244. Soybean standard error (s_X) for a single sensor was 4.48% and with six sensors was 1.83% of the final CI-PAR. Maize s_X for a single sensor was 5.29% and with eight sensors was 1.87% of the final CI-PAR. Crop biomass was quantified weekly by collecting four 1 m² samples. Soybean RUE using all sensors was 1.44 ± 0.06 g MJ PAR⁻¹. The highest CI-PAR from a single sensor had RUE of 1.32 and the lowest was 1.55 g MJ PAR⁻¹. Maize RUE using all sensors was 3.35 ± 0.09. The highest CI-PAR from a single sensor had RUE of 2.87 and the lowest was 3.70 g MJ PAR⁻¹. Reliable transmitted PAR and RUE estimates are obtainable at the field-scale in maize and soybean with four and three sensors, respectively, assuming that crop biomass is accurately measured.     

Understanding the relationships between genetic and phenotypic structures of a collection of elite durum wheat accessions

A collection of 191 durum wheat accessions representing Mediterranean Basin genetic diversity was grown in nine different environments in four countries, with productivities ranging from 0.99 to 6.78 t ha⁻¹. The population breeding structure comprised eight genetic subpopulations (GSPs) using data derived from 97 evenly distributed SSR markers. The phenotypic structure was assessed: (i) from the mean values of six agronomic traits across environments (multivariate), and (ii) from data representing each trait in each environment (univariate). Mean daily maximum temperature from emergence to heading was significantly (P < 0.05) and negatively associated to yield, accounting for 59% of yield variations. Significant but weak relationships were obtained between the genetic similarities among accessions and their overall agronomic performance (r = 0.15, P < 0.001), plant height (r = 0.12, P < 0.001), spike–peduncle length (r = 0.06, P < 0.01) and thousand kernel weight (r = 0.03, P < 0.05), suggesting a very low possibility of prediction of the agronomic performance based on random SSR markers. The percentage of variability (measured by sum of squares) explained by the environment varied between 76.3 and 98.5% depending on the trait, while that explained by genotypes ranged between 0.4 and 12.6%, and that explained by the GE interaction ranged from 1.1 to 12.5%. The clustering of the accessions based on multivariate phenotypic data offered the best explanation of genotypic differences, accounting for 30.3% (for yield) to 75.1% (for kernel weight) of the observed variation. The genotype × environment interaction was best explained by the phenotypic univariate clustering procedure, which explained from 28.5% (for kernel weight) to 74.9% (for days to heading) of variation. The only accessions that clustered both in the genetic dissimilarities tree and the tree obtained using Euclidean distances based on standardized phenotypic data across environments were those closely related to the CIMMYT hallmark founder ‘Altar 84’, the ICARDA accessions adapted to continental-dryland areas, and the landraces, suggesting that genetic proximity corresponded to agronomic performance in only a few cases.     

Regeneration in Jatropha curcas: Factors affecting the efficiency of in vitro regeneration

Factors influencing in vitro regeneration through direct shoot bud induction from hypocotyl explants of Jatropha curcas were studied in the present investigation. Regeneration in J. curcas was found to be genotype dependent and out of four toxic and one non-toxic genotype studied, non-toxic was least responsive. The best results irrespective of genotype were obtained on the medium containing 0.5 mg L⁻¹ TDZ (Thidiazuron) and in vitro hypocotyl explants were observed to have higher regeneration efficiency as compared to ex vitro explant in both toxic and non-toxic genotypes. Adventitious shoot buds could be induced from the distal end of explants in all the genotypes. The number of shoot buds formed and not the number of explants responding to TDZ treatment were significantly affected by the position of the explant on the seedling axis. Explants from younger seedlings (≤15 days) were still juvenile and formed callus easily, whereas the regeneration response declined with increase in age of seedlings after 30 days. Transient reduction of Ca²⁺ concentrations to 0.22 g L⁻¹ in the germination medium increased the number of responding explants.Induced shoot buds, upon transfer to MS medium containing 2 mg L⁻¹ Kn (Kinetin) and 1 mg L⁻¹ BAP (6-benzylamino purine) elongated. These elongated shoots were further proliferated on MS medium supplemented with 1.5 mg L⁻¹ IAA (indole-3-acetic acid) and 0.5 mg L⁻¹ BAP and 3.01-3.91 cm elongation was achieved after 6 weeks. No genotype specific variance in shoot elongation was observed among the toxic genotypes except the CSMCRI-JC2, which showed reduced response. And for proliferation among the toxic genotypes, CSMCRI-JC4 showed highest number of shoots formed. Among the rest, no significant differences were observed. The elongated shoot could be rooted by pulse treatment on half-strength MS medium supplemented with 2% sucrose, 3 mg L⁻¹ IBA (indole-3-butyric acid), 1 mg L⁻¹ IAA, 1 mg L⁻¹ NAA (α-naphthalene acetic acid) and subsequent transfer on 0.25 mg L⁻¹ activated charcoal medium. The rooted plants could be established in soil with more than 90% success. No significant differences were observed in rooting of shoots in the different toxic genotypes. However, rooting response was reduced in non-toxic genotype as compared to toxic genotypes.     

Effect of boron on the development of brown rot (Monilinia laxa) on peaches

Requirements of consumers for products with low residues of pesticides have increased the need for alternative disease management practices. The concentration of boron in fruit affects its quality, shelf life and the development of physiological disorders. However, the effect of boron on the susceptibility of peach to fruit rots has not been reported. This study investigated the effect of boron (Power B and Borax) on the development of Monilinia laxa on peaches (cv Andross). Mycelial growth of M. laxa was inhibited on potato dextrose agar supplemented with 750 μg ml⁻¹ of Borax or 1000 μg ml⁻¹ of Power B. The EC 50 values were 107.9 and 522.4 for Borax and Power B respectively. Field investigations showed that the incidence of peach infections by M. laxa was negatively correlated with the content of Boron in the leaves. Post-harvest dipping of peaches in Power B or Borax solution, at concentrations recommended by manufacturer (2 μg ml⁻¹ for Power B and 1 mg ml⁻¹ for Borax), significantly reduced the development of M. laxa. Power B, at rates of 6 μg ml⁻¹, and Borax at rates of 3 mg ml⁻¹ were the most effective in reducing infections by M. laxa. Finally, post-harvest dipping of fruit in Power B or Borax reduced losses of fruit weight and improved fruit firmness one month after storage, showing that boron increased the maintainability of peaches in cold storage. Peaches treated with 6 μg ml⁻¹ Power B or 3 mg ml⁻¹ Borax had the highest flesh firmness and the lowest water losses, while untreated control peaches were the least firm. Generally, Borax was significantly less effective than Power B, but better than the control treatment.     

Synthesis of withanolide A depends on carbon source and medium pH in hairy root cultures of Withania somnifera

Withania somnifera (L.) Dunal. (Indian ginseng) is an important medicinal plant which yields pharmaceutically active compounds called withanolides. The present work deals with optimization of parameters of hairy root culture of W. somnifera for the production of biomass and withanolide A. We also investigated the effects of carbon source [sucrose, glucose, fructose, maltose, glucose + fructose (1:1), fructose + sucrose (1:1) and sucrose + glucose (1:1)], sucrose concentration (1%, 2%, 3%, 4%, 6% and 8%) and the initial medium pH (4.0, 4.5, 5.0, 5.5, 5.8, 6.0 and 6.5) on growth and production of withanolide A in hairy root cultures of W. somnifera. We found that biomass accumulation and production of withanolide A was highest when sucrose was used as the carbon source (11.92 g l⁻¹ DW and 11.96 mg g⁻¹ DW of withanolide A). Further 3% sucrose concentration was found to be optimal for biomass accumulation (11.92 g l⁻¹ DW) and 4% sucrose favoured the production of withanolide A (13.28 mg g⁻¹ DW) in the tested range of concentrations (1-8%). The biomass of hairy roots was optimal when the initial medium pH was 5.8 (12.1 g l⁻¹ DW) and the withanolide A production was highest in the medium pH set at 6.0 (13.84 mg g⁻¹ DW).