Stand establishment and early field vigour variation in a tropicalised shrunken-2 maize population

Low field emergence and early field vigour are major problems in shrunken-2 maize (sh-2). The genetic variability for stand-ability and early field vigour in a shrunken-2 maize population previously improved for adaptability to a tropical environment was investigated using a Design I mating system in which 40 randomly sampled males were crossed to four randomly sampled plants that served as females. Plants of the 160 crosses, representing full- and half-sib relationships, were evaluated in four sets, each composed of 40 crosses derived from 10 males during two growing seasons. Experimental design was randomized complete block with three replications. Difference in Emergence Index (EI) was not significant between the two seasons. Emergence Percentage (E%), Emergence Rate Index (ERI), and early field vigour traits viz. vigour score and seedling height determined at 28 days after planting (DAP) were, however, significantly (P < 0.05–P < 0.01) better in the first growing season. For all traits, the ‘female/male’ item was significant (P < 0.01) while ‘male’ was mostly non-significant. ‘Season × female/male’ interaction was significant for stand establishment traits but not for early field vigour traits. Averaged over all traits, dominance variance was 8.2 times higher than additive variance. Genetic variation for stand establishment and early field vigour in the tropicalised shrunken-2 maize population would be best exploited through the development of inbred lines, hybrids and synthetics. Broad-sense heritability was 53.0% for E%, 36.0% for EI, 33.0% for ERI, 71.5% for vigour score and 90.0% for seedling height. One hundred-seed weight ranged between 82.0 and 182.0 mg but correlation coefficients between seed weight on one hand, and E%, EI, ERI, vigour score and plant height on the other hand, were low (mostly <0.30) and, in general, non-significant. Emergence percentage had the highest average genotypic correlation value with the other traits studied (Mean Absolute Value = 0.71 in the first season and 0.45 in the second season). Emergence percentage, determined 10 days after planting, thus has potential for use as a selection index for stand establishment and early field vigour.     

Genotypic variation for root traits of maize (Zea mays L.) from the Purhepecha Plateau under contrasting phosphorus availability

Phosphorus (P) deficiency is a major constraint for maize production in many low-input agroecosystems. This study was conducted to evaluate genotypic variation in both root (root architecture and morphology, including root hairs) and plant growth traits associated with the adaptation of maize landraces to a P-deficient Andisol in two locations in the Central Mexican highlands. Two hundred and forty-two accessions from the Purhepecha Plateau, Michoacan were grown in Ponzomaran with low (23 kg P₂O₅ ha⁻¹) and high (97 kg P₂O₅ ha⁻¹) P fertilization under rain-fed field conditions, and subsequently a subset of 50 contrasting accessions were planted in the succeeding crop cycle in Bonilla. Accessions differed greatly in plant growth, root morphology and P efficiency defined as growth with suboptimal P availability. The accessions were divided into 3 categories of P efficiency using principal component and cluster analyses, and 4 categories according to the retained principal component and their relative weight for each genotype in combination with growth or yield potential. The distribution of accessions among three phosphorus efficiency classes was stable across locations. Phosphorus-efficient accessions had greater biomass, root to shoot ratio, nodal rooting, nodal root laterals, and nodal root hair density and length of nodal root main axis, and first-order laterals under P deficiency. Biomass allocation to roots, as quantified by the allometric partitioning coefficient (K) was not altered by P availability in the efficient accessions, but inefficient accessions had a lower K under low P conditions. Accessions with enhanced nodal rooting and laterals had greater growth under low P. Dense root hairs on nodal root main axes and first-order laterals conferred a marked benefit under low P, as evidenced by increased plant biomass. Late maturity improved growth and yield under low P. These results indicate that landraces of the Central Mexican highlands exhibit variation for several root traits that may be useful for genetic improvement of P efficiency in maize.     

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.     

Effects of fungicide seed treatments on germination, population, and yield of maize grown from seed infected with fungal pathogens

Seedborne fungi can reduce survival, growth, and yield of maize (Zea mays L.). Laboratory, field, and growth chamber experiments were conducted to determine the effects of the seed treatment fungicides fludioxonil, mefenoxam, and azoxystrobin on germination, plant population, and grain yield of maize grown from low-quality hybrid seed infected with seedborne fungal pathogens. Study I used seed of four hybrids infected at 0-54% incidence with Fusarium spp., Stenocarpella maydis, Penicillium spp., Rhizopus spp., and/or Aspergillus spp. Study II used three seed lots for each of two hybrids infected at 7-37% incidence with S. maydis. Warm and cold germination for untreated seed varied among hybrids in both studies. Warm germination of the seed lot with the highest incidence of S. maydis in study II treated with azoxystrobin and fludioxonil was significantly greater (+7%) than the nontreated control. Plant population in study I was significantly affected by seed treatment, hybrid, and their interactions. Populations were greater (≥9%) for fludioxonil, fludioxonil + mefenoxam, and fludioxonil + mefenoxam + azoxystrobin treatments compared to controls. In growth chamber experiments with pasteurized soil, emergence (≥5%) and plant dry weight (≥14%) were both greater than controls only with the triple seed treatment. Plant populations in study II for all seed treatments except mefenoxam and azoxystrobin alone were greater (≥4%) than controls. Yield in study I was significantly affected by hybrid and seed treatment. Yield for one hybrid was higher (≥20%) than the control with all seed treatments except fludioxonil, whereas yield with another hybrid was consistently greater (≥26%) only with the triple seed treatment. Yield in study II was significantly affected by hybrid, seed treatment, and their interactions. Yield was greater (≥8%) than the controls for all seed treatments with one hybrid and with all (≥5%) except azoxystrobin for the other hybrid. Highest yields occurred with the triple seed treatment. Results indicate that fludioxonil and azoxystrobin can increase germination, population, and yield of maize grown from seed infected by S. maydis and other fungi.     

Improvement of growth and gymnemic acid production by altering the macro elements concentration and nitrogen source supply in cell suspension cultures of Gymnema sylvestre R. Br

Gymnema sylvestre is an important medicinal plant which bears bioactive compound namely gymnemic acids. The present work deals with optimization of cell suspension culture system of G. sylvestre for the production of biomass and gymnemic acid and we investigated effects of macro elements (NH₄NO₃, KNO₃, CaCl₂, MgSO₄ and KH₂PO₄ - 0.0, 0.5, 1.0, 1.5 and 2.0× strength) and nitrogen source [NH₄⁺/NO₃⁻ ratio of: 0.00/18.80, 7.19/18.80, 14.38/18.80, 21.57/18.80, 28.75/18.80, 14.38/0.00, 14.38/9.40, 14.38/18.80, 14.38/28.20 and 14.38/37.60 (mM)] of Murashige and Skoog medium on accumulation of biomass and gymnemic acid content. The highest accumulation of biomass (165.00 g l⁻¹ FW and 15.42 g l⁻¹ DW) was recorded in the medium with 0.5× concentration of NH₄NO₃ and the highest production of gymnemic acid content was recorded in the medium with 2.0× KH₂PO₄ (11.32 mg g⁻¹ DW). The NH₄⁺/NO₃⁻ ratio also influenced cell growth and gymnemic acid production; both parameters were greater when the NO₃⁻ concentration was higher than that of NH₄⁺. Maximum biomass growth (159.72 g l⁻¹ of FW and 14.95 g l⁻¹ of DW) was achieved at an NH₄⁺/NO₃⁻ ratio of 7.19/18.80, and gymnemic acid production was also greatest at the same concentration of NH₄⁺/NO₃⁻ ratio (11.35 mg g⁻¹ DW).     

Analysis of QTL for resistance to head smut (Sporisorium reiliana) in maize

Head smut of maize, caused by the fungus Sporisorium reiliana, is an important disease in the temperate maize-growing areas worldwide. In this study, we mapped and characterized quantitative trait loci (QTL) conferring resistance to S. reiliana using a F_2:3 population of 184 families derived from a cross between Mo17 (resistant parent) and Huangzao4 (susceptible). The population was evaluated for resistance in replicated field trials with artificial inoculation of S. reiliana chlamydospores in Gongzhuling of Jilin Province and Harbin of Heilongjiang Province of China, two hot spots of head smut incidence, in 2003 and 2004. Genotypic and G × E variances for disease incidence were highly significant in the population. Heritability estimates for percentage disease incidence in the 2-location and 2-year evaluation ranged from 0.62 to 0.70. Composite interval mapping on a linkage map (1956.1 cM distance; 9.34 cM average interval) constructed with 84 SSR and 135 AFLP markers, identified five QTL, one each on chromosomes 1, 3 and 8 and two on chromosome 2, accounting for 5.0–43.7% of the phenotypic variance across four environments. One major QTL on chromosome 2 explaining up to 43.7% of the phenotypic variance can potentially be used in molecular marker-assisted selection for head smut resistance in maize.     

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).     

Genetic analysis of field resistance to tan spot in spring wheat

Tan spot, caused by Pyrenophora tritici-repentis (Died.) Drechs., is an important constraint to wheat (Triticum aestivum L.) yield in many countries. Since the inheritance of field resistance to tan spot is poorly understood, this study was conducted to determine the genetic control of resistance in the field. Resistance was measured as disease severity caused by P. tritici-repentis race 1 in four crosses involving five wheat parents: parent 1 (P₁) = catbird; parent 2 (P₂) = Milan/Shanghai-7; parent 3 (P₃) = Alondra/Coc//Ures; parent 4 (P₄) = Bcb//Dundee/Gul/3/Gul); parent 5 (P₅) = ND/VG9144//Kal/BB/3/Yaco/4/Chil. P₁, P₂ and P₃ were resistant and P₄ was moderately resistant, whereas P₅ was susceptible to tan spot. The F₂-derived F₃ families and the parents were field evaluated at El Batán, Mexico, in 1996. When all the plants within a F₃ family expressed low levels of disease severity similar to that of the resistant parent it was classified resistant (R), otherwise the progeny was classified as susceptible (S). The progeny of the three crosses of the susceptible parent with the resistant and moderately resistant parents P₂, P₃, and P₄ segregated as 3R:13S whereas the progeny in the cross with P₁ showed a segregation ratio of 1R:15S. This suggests that each resistant parent possessed two genes conditioning resistance to tan spot severity caused by P. tritici-repentis race 1. Information on the inheritance of resistance measured as disease severity on adult plants under field conditions is of practical importance for wheat breeding programs seeking improvement in tan spot resistance.     

Relationship between P and N concentrations in maize and wheat leaves

Simple plant-based diagnostic tools can be used to determine crop P status. Our objectives were to establish the relationships between P and N concentrations of the uppermost collared leaf (P_L and N_L) of spring wheat (Triticum aestivum L.) and maize (Zea mays L.) during the growing season and, in particular, to determine the critical leaf P concentrations required to diagnose P deficiencies. Various N applications were evaluated over six site-years for wheat and eight site-years for maize (2004-2006) with adequate soil P for growth. Phosphorus and N concentrations of the uppermost collared leaf were determined weekly and the relationships between leaf N and P concentrations were established using only the sampling dates from the stem elongation stage for wheat and from the V8 stage of development for maize. Leaf P concentration generally decreased with decreasing N fertilization. Relationships between P_L and N_L concentrations (mg g⁻¹ DM) using all site-years and sampling dates were described by significant linear-plateau functions in both maize (P_L = 0.82 + 0.089 N_L if N_L ≤ 32.1 and P_L = 3.7 if N_L > 32.1; R² = 0.41; P < 0.001) and wheat (P_L = 0.02 + 0.106 N_L if N_L ≤ 33.2 and P_L = 3.5 if N_L > 33.2; R² = 0.42; P < 0.001). Variation among sampling dates in the relationships were noted. By restricting the sampling dates [413-496 growing degree days (5 °C basis) in wheat (i.e., stem elongation) and 1494-1579 crop heat units in maize (i.e., silking), relationships for wheat (P_L = 0.29 + 0.073 N_L, R² = 0.66; P < 0.001) and maize (P_L = 1.04 + 0.084 N_L, R² = 0.66; P < 0.001) were improved. In maize, expressing P and N concentrations on a leaf area basis (P_LA and N_LA) at silking further improved the relationship (P_LA = 0.002 + 0.101 N_LA, R² = 0.80; P < 0.001). Predictive models of critical P concentration as a function of N concentration in the uppermost collared leaf of wheat and maize were established which could be used for diagnostic purposes.     

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.     

Simultaneous selection for stem borer resistance and forage related traits in maize (Zea mays ssp. mays L.) × teosinte (Zea mays ssp. mexicana L.) derived populations

Maize spotted stalk borer (Chilo partellus Swinhoe Pyralidae) (MSSB) is a serious pest of the maize (Zea mays ssp. mays L.) crop in Pakistan. This study was conducted to introgress resistance in maize against MSSB by exploring wild sources of resistance for the development of a resistant maize variety. To achieve this, teosinte (‘PI566674’) × maize (‘Sargodha-2002’) crosses were conducted and three populations (F₁, F₂ and F₃) were established. These populations were screened at various locations and in a contrasting artificial insect infestation experiment. Teosinte species ‘PI566674’, following screening, was shown to be highly resistant to MSSB and had the ability to produce a high biomass (5 times higher than susceptible genotypes) under high temperatures (36–40 °C). The biomass of the F₁ hybrid, which was highly susceptible to MSSB, was significantly reduced (P ≤ 0.05) following infestation by MSSB in all experiments. The introgression from teosinte for genes conferring resistance to MSSB was screened in segregating F₂ and F₃ generations. Despite a susceptible F₁ population, F₂ was resistant to MSSB. Twenty new recombinant plants with resistance to MSSB and a high leaf soluble solid (16 °Brix) content were identified. They were selected to grow the F₃ population. Mean values of F₃ progenies showed similar resistance to the F₂ population but a high percentage (60%) of resistant plants was recovered.     

Genetic structure of natural Tunisian Hypericum humifusum L. (Hypericacae) populations as assessed by allozymes and RAPDs

The genetic diversity within and among seven Tunisian natural populations of Hypericum humifusum L., from different geographic regions and bioclimates, was assessed using 11 isozymic polymorphic loci, and 166 RAPD markers amplified by 8 primers. The genetic diversity within populations based on allozymes was higher (P = 72.46%, Ap = 2.01 and H_e = 0.29), than that revealed by RAPDs (29.52 < P < 39.16% and 0.150 < H < 0.200). Both markers yielded high estimates of genetic differentiation and low gene flow (Nm = 0.257 and 0.508 for RAPD and allozymes, respectively) among populations at all space scales. However, the level of differentiation revealed by RAPDs (Φ_ST = 0.494; G_ST = 0.561) was higher than that based on allozymes (F_ST = 0.117). No correlation (Mantel test) among genetic (F_ST and Φ_ST matrices) and geographical distance matrices was observed indicating no isolation by distance. Cluster analyses from allozyme and RAPD loci did not completely agree. The dendrogram based on allozymes yielded higher separation among most populations, while that from RAPDs separated populations into three distinct subclusters. Groupings of populations, in both dendrograms, did not reflect spatial geographic or bioclimatic patterns, indicating specific adaptation of populations to local environments. The correlation between matrices of allozyme and RAPD band frequencies was not significant (Mantel test). The dendrogram obtained from combined data yielded similar population groupings to that probed by RAPDs suggesting higher accuracy of these markers. Given the high differentiation among all populations even at a low geographic distance, ex situ conservation should involve extensive seed collection from all populations from all bioclimatic zones. The populations from the upper semi-arid bioclimate exhibiting relatively high level of genetic diversity should be first protected.     

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.     

Inter-plant competition for resources in maize crops grown under contrasting nitrogen supply and density: Variability in plant and ear growth

Increased plant population density in irrigated and fertilized maize crops enhances plant-to-plant variability since early vegetative stages, because the most suppressed individuals of the stand intercept less radiation per unit leaf area than the dominant ones (i.e. a size-asymmetric competition for light). Contrarily, a size-symmetric competition has been proposed for the acquisition of soil resources in a plant community (e.g. N capture per unit root length is similar among plants of different size). Hence, N fertilization effect on the variability of maize plants would depend on the initial plant-to-plant variability or on that promoted by a high plant population density. Two maize hybrids with contrasting tolerance to crowding (tolerant AX820 and intolerant AX877) were cultivated under different combinations of stand densities (6, 9 and 12 plants m⁻²) and N supplies (0 and 200 kg N ha⁻¹) without water restrictions. Variability in plant growth rate among plants was computed along the cycle, especially after fertilizer was applied (i.e. the early reproductive period; PGR_ER) and during the critical period around silking (PGR_CP). Plant-to-plant variability in biomass partitioning to the ear (partition index; PI), ear growth rate during the critical period (EGR_CP) and kernel number per plant (KNP) was also established. Reduced N supply increased the coefficient of variation (CV) of PGR_ER, PGR_CP, EGR_CP and KNP (0.05 < P < 0.10). The CVs of PGR_CP, PI, EGR_CP and KNP augmented (0.001 < P < 0.10) at the highest stand density. The CVs of PGR_ER, PGR_CP, PI and KNP were larger for hybrid AX877 than for hybrid AX820 (0.001 < P < 0.10). N fertilization smoothed the initial plant-to-plant variability, but the extent of this benefit in a maize crop is genotype dependent; it was much larger in the hybrid tolerant to crowding stress than in the intolerant one. For the latter, the variability held during the critical period around silking and produced a high CV of KNP.     

High-yield irrigated maize in the Western U.S. Corn Belt: I. On-farm yield,yield potential,and impact of agronomic practices

Quantifying the exploitable gap between average farmer yields and yield potential (Y_P) is essential to prioritize research and formulate policies for food security at national and international levels. While irrigated maize accounts for 58% of total annual maize production in the Western U.S. Corn Belt, current yield gap in these systems has not been quantified. Our objectives were to quantify Y_P, yield gaps, and the impact of agronomic practices on both parameters in irrigated maize systems of central Nebraska. The analysis was based on a 3-y database with field-specific values for yield, applied irrigation, and N fertilizer rate (n = 777). Y_P was estimated using a maize simulation model in combination with actual and interpolated weather records and detailed data on crop management collected from a subset of fields (n = 123). Yield gaps were estimated as the difference between actual yields and simulated Y_P for each field-year observation. Long-term simulation analysis was performed to evaluate the sensitivity of Y_P to changes in selected management practices. Results showed that current irrigated maize systems are operating near the Y_P ceiling. Average actual yield ranged from 12.5 to 13.6 Mg ha⁻¹ across years. Mean N fertilizer efficiency (kg grain per kg applied N) was 23% greater than average efficiency in the USA. Rotation, tillage system, sowing date, and plant population density were the most sensitive factors affecting actual yields. Average yield gap was 11% of simulated Y_P (14.9 Mg ha⁻¹). Time trends in average farm yields from 1970 to 2008 show that yields have not increased during the past 8 years. Average yield during this period represented ∼80% of Y_P ceiling estimated for this region based on current crop management practices. Simulation analysis showed that Y_P can be increased by higher plant population densities and by hybrids with longer maturity. Adoption of these practices, however, may be constrained by other factors such as difficulty in planting and harvest operations due to wet weather and snow, additional seed and grain drying costs, and greater risk of frost and lodging. Two key points can be made: (i) irrigated maize producers in this region are operating close to the Y_P ceiling and achieve high levels of N use efficiency and (ii) small increases in yield (<13%) can be achieved through fine tuning current management practices that require increased production costs and higher risk.     

Nitrogen efficiency in long-term wheat–maize cropping systems under diverse field sites in China

Efficiency of fertilizer N is becoming increasingly important in modern agricultural production owing to increasing food requirement and growing concern about environments. However, there is almost no study regarding its long-term efficiency in wheat and maize cropping systems. Long-term (15 years) experiments involving wheat (Triticum aestivum L.) and maize (Zea mays L.) rotations at five field sites with various soil and climate characteristics in China were used to determine the nitrogen (N) efficiency, including the physiological efficiency, recovery efficiency and N mass balance of soil–plant systems in response to different fertilization treatments. The present study consisted of nine treatments: unfertilized, N, phosphorus, potassium, straw and manure or their combinations. The contribution of N fertilizers to wheat yield was higher than to maize and suggested that wheat could be given priority over maize when determining N application rates. Uptake of 1 kg N produced 35.6 kg of wheat grain and 39.5 kg of maize grain. The deficit of N in soils without applied N ranged from 40 to 103 kg N ha⁻¹ year⁻¹, while N surpluses in soils with applied N fertilizers ranged from 35 to 350 kg N ha⁻¹ year⁻¹. The apparent accumulated N recovery efficiency (NRE_ac) varied widely from 4% to 90%: unbalanced fertilization and other soil limiting factors (such as aluminium toxicity) were associated with low NRE_ac. In the treatments of combination of N, phosphorus and potassium with normal application rates, the average of NRE_ac in four out of five sites reached 80%, which suggested that best management of N fertilizers could recover most of N fertilizers applied to soils. The results will be helpful to understand the long-term fate of N fertilizers and to optimize the N fertilization for agricultural practices and environment protection.     

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.     

‘On-farm’ seed priming with zinc sulphate solution—A cost-effective way to increase the maize yields of resource-poor farmers

The effect of adding zinc sulphate (ZnSO₄) to maize (Zea mays L.) growing on calcareous, Zn deficient soils in the North West Frontier Province of Pakistan was assessed in vitro, on-station and in on-farm trials. The zinc sulphate was added either as a powder to the soil or by soaking seeds for 16 h in dilute solutions prior to sowing. For the first time in maize, we separated the benefits of priming simply with water from those provided by added zinc.     

Transgressive variants for red pericarp grain with high yield potential derived from Oryza rufipogon × Oryza sativa: Field evaluation, screening for blast disease, QTL validation and background marker analysis for agronomic traits

Five transgressive variants (advanced breeding lines from BC₂F₅ and BC₂F₆ generation) were derived from a cross between the wild relative, O. rufipogon Griff. and O. sativa L. subsp. indica cv. MR219, a popular high yielding Malaysian rice cultivar. The aim of the study was to evaluate the pericarp colour of the grains along with yield potential and to validate quantitative trait loci (QTLs) for agronomic traits. The variants were screened against blast disease. Background marker analysis was also done for the promising variants. The field trials were carried out at a single location (due to containment purposes) over two seasons using randomized complete block design (RCBD) with three replications. A trait-based marker analysis was used to identify QTLs for validation in BC₂F₅ generation. Analysis of variance (ANOVA) showed that the seasonal factors influenced different agronomic traits. Variant G33 produced significantly (p < 0.05) higher yield (5.20 t/ha) than the control, MR219 (4.53 t/ha). Eighteen QTLs for different agronomic traits were identified in BC₂F₂ population in a previous study. Among them 14 QTLs were found in BC₂F₅ population of the present study. The yield of variant G33 was influenced by several QTLs viz. qGPL-1, qSPL-1-2, qSPL-8 and qYLD-4, which were introgressed from the donor parent revealed by background marker analysis using BC₂F₇ generation. Percentage (99%) of red pericarp grain of G33 and G34 in BC₂F₅ and BC₂F₆ generations indicated the stability of pericarp colour which was transferred from the wild relative. Variant G33 showed resistance against two pathotype of blast disease (Magnaporthe oryzae). Among the evaluated variants, G33 could be considered for inclusion in the cultivar development program for red rice with high yield potential and resistance to blast disease. This study demonstrated that the alleles from wild relative could improve the yield and yield related traits through allelic interaction, even though the phenotypic traits were inferior to the recurrent parent.     

Ecological studies on Echinochloa crus-galli and the implications for weed management in direct-seeded rice

Echinochloa crus-galli, a C₄ grass, is one of the world’s most serious weeds. Weed management decisions for this species can be derived from knowledge of its seed biology. Studies were conducted to determine the effects of light on germination; seed burial depth and rice residue on emergence and growth; and flooding time and depth on emergence, survival and growth of this species. Light stimulated seed germination but it was not an absolute requirement for germination. The proportion of seeds germinating was greatest for seeds placed on the soil surface (92%), and emergence declined with increasing burial depth in soil; no seedlings emerged from the depth of 8 cm. A burial depth of only 0.4 cm reduced seedling emergence by 50%. Seedling emergence and seedling biomass were reduced by the addition of high level (6 ton ha⁻¹) of rice residue to the soil surface. Early and deep flooding significantly suppressed growth of E. crus-galli seedlings. In flooded conditions, with increased water depth the weed allocated more biomass to shoots at the expense of roots. The information gained from this study could contribute to improve weed control approaches. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence, use of crop residue as mulch and early flooding of the crop could serve as important tools for managing E. crus-galli and other weed species with similar germination requirements. These management options, however, would need to be compatible with other crop management requirements.