Stratification of SADC regional sorghum testing sites based on grain yield of varieties

We applied sequential retrospective (SeqRet) pattern analysis to stratify sorghum variety testing sites according to their similarity for yield discrimination among genotypes using historical grain yield data from 147 multi-environment trials (METs). The trials were conducted at 38 sites in 10 countries of the Southern African Development Community (SADC) region during 1987/1988–1992/1993 and 1999/2000. The analysis for the 6 years 1987/1988–1992/1993, covering 34 sites, clustered these sites into 6 major groups with a model fit of R² = 0.75. With additional data from the year 1999/2000, the SeqRet pattern analysis delivered a very similar clustering of the 34 sites, with the additional four sites in 1999/2000 properly classified with appropriate site groups (R² = 0.74). The results suggest that future sorghum variety testing could be restricted to a few representative sites selected from within each of the six identified site-groups.     

Stratification of SADC regional pearl millet testing sites based on grain yield performance of lines

Sequential retrospective (SeqRet) pattern analysis was used to stratify pearl millet testing sites according to their similarity of line-yield differentiation using grain yield data from 90 multi-environment trials (METs) conducted in the Southern African Development Community (SADC) region. The METs, conducted across 25 sites over 9 years were split into two sets: Set 1 (1989/1990–1992/1993) included introductory genetic materials, and Set 2 (1994/1995–1998/1999) included advanced genetic materials. Site stratification analysis from Set 1 and Set 2 partitioned the testing sites into six and five groups with R²-values of 76 and 79%, respectively. Analysis of the cumulative dataset (1989/1990–1998/1999) clustered the 25 sites into six groups with R²=76% and captured the major patterns of site similarities in Set 1 and Set 2. Based on our experience from running multi-year METs in the SADC region, the cumulative dataset was more informative in judging the relevance of site-stratification results. SeqRet pattern analysis, exploiting available highly imbalanced historical MET data, provided an objective basis for stratifying the test-sites to facilitate selection of a few representative test-sites for future testing of lines. The results from cumulative dataset suggest that future line testing could be restricted to a few sites picked from within each of the identified site-groups.     

A model for simulating plant N accumulation,growth and yield of diverse rice genotypes grown under different soil and climatic conditions

The objective of this study was to develop a whole-process model for explaining genotypic and environmental variations in the growth and yield of irrigated rice by incorporating a newly developed sub-model for plant nitrogen (N) uptake into a previously reported model for simulating growth and yield based on measured plant N. The N-uptake process model was developed based on two hypotheses: (1) the rate of root system development in the horizontal direction is proportional to the rate of leaf area index (LAI) development, and (2) root N-absorption activity depends on the amount of carbohydrate allocated to roots. The model employed two empirical soil parameters characterizing indigenous N supply and N loss. Calibration of the N-uptake process sub-model and validation of the whole-process model were made using plant N accumulation, and growth and yield data obtained from a cross-locational experiment on nine rice genotypes at seven locations in Asia, respectively. Calibration of the N-uptake process sub-model indicated that a large genotypic difference exists in the proportionality constant between rate of root system development and that of LAI development during early growth stages. The whole-process model simultaneously explained the observed genotypic and environmental variation in the dynamics of plant N accumulation (R² = 0.91 for the entire dataset), above-ground biomass growth (R² = 0.94), LAI development (R² = 0.78) and leaf N content (R² = 0.79), and spikelet number per unit area (R² = 0.78) and rough grain yield (R² = 0.81). The estimated value of the site (field)-specific soil parameter representing the rate of N loss was negatively correlated with cation exchange capacity of the soil and was approximated by a logarithmic function of cation exchange capacity for seven sites (R² = 0.95). Large yearly and locational variations were estimated in the soil parameter for representing the rate of indigenous N supply at 25 °C. With the use of these two soil parameters, the whole-system model explained the observed genotypic and environmental variations in plant N accumulation, growth and yield of rice in Asia.     

Multivariate analysis of nitrogen content for rice at the heading stage using reflectance of airborne hyperspectral remote sensing

Airborne hyperspectral remote sensing was adapted to establish a general-purpose model for quantifying nitrogen content of rice plants at the heading stage using three years of data. There was a difference in dry mass and nitrogen concentration due to the difference in the accumulated daily radiation (ADR) and effective cumulative temperature (ECT). Because of these environmental differences, there was also a significant difference in nitrogen content among the three years. In the multiple linear regression (MLR) analysis, the accuracy (coefficient of determination: R², root mean square of error: RMSE and relative error: RE) of two-year models was better than that of single-year models as shown by R² ≥ 0.693, RMSE ≤ 1.405 g m⁻² and RE ≤ 9.136%. The accuracy of the three-year model was R² = 0.893, RMSE = 1.092 g m⁻² and RE = 8.550% with eight variables. When each model was verified using the other data, the range of RE for two-year models was similar or increased compared with that for single-year models. In the partial least square regression (PLSR) model for the validation, the accuracy of two-year models was also better than that of single-year models as R² ≥ 0.699, RMSE ≤ 1.611 g m⁻² and RE ≤ 13.36%. The accuracy of the three-year model was R² = 0.837, RMSE = 1.401 g m⁻² and RE = 11.23% with four latent variables. When each model was verified, the range of RE for two-year models was similar or decreased compared with that for single-year models. The similarities and differences of loading weights for each latent variable depending on hyperspectral reflectance might have affected the regression coefficients and the accuracy of each prediction model. The accuracy of the single-year MLR models was better than that of the single-year PLSR models. However, accuracy of the multi-year PLSR models was better than that of the multi-year MLR models. Therefore, PLSR model might be more suitable than MLR model to predict the nitrogen contents at the heading stage using the hyperspectral reflectance because PLSR models have more sensitive than MLR models for the inhomogeneous results. Although there were differences in the environmental variables (ADR and ECT), it is possible to establish a general-purpose prediction model for nitrogen content at the heading stage using airborne hyperspectral remote sensing.     

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.     

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.     

Soybean yield trends from 1972 to 2003 in mid-western USA

The increases in crop yield that played an important role in maintaining adequate food supplies in the past may not continue in the future. Soybean (Glycine max L. Merrill) county yield trends (1972–2003) were examined for evidence of plateaus using data (National Agricultural Statistics Service) for 162 counties (215 data sets) in six production systems [Iowa, Nebraska (irrigated and non-irrigated), Kentucky and Arkansas (irrigated and non-irrigated)] representing a range in yield potential. Average yield (1999–2003) was highest in irrigated production in Nebraska (3403 kg ha⁻¹) and lowest in non-irrigated areas in Arkansas (1482 kg ha⁻¹). Average yield in the highest yielding county in each system was 31–88% higher than the lowest. Linear regression of yield versus time was significant (P = 0.05) in 169 data sets and a linear-plateau model reached convergence (with the intersection point in the mid-1990s) in 35 of these data sets, but it was significantly (P = 0.10) better in only three data sets (<2% of the total). Absolute (kg ha⁻¹ year⁻¹) growth rates were associated with productivity, but relative rates were not with the mean relative rates ranging from 1.0 to 1.3% over the six systems. There was, however, a two- to threefold range in relative rate among counties within systems in Nebraska, Iowa, Kentucky and Arkansas (irrigated). Yield did not change (linear regression not significant, P = 0.05) between 1972 and 2003 in 41 counties in non-irrigated areas of Arkansas and Nebraska and in six Kentucky counties of which four had high levels of double-cropping soybean after wheat (Triticum aestivum L.). I found no convincing evidence that soybean yields are reaching plateaus but the technology responsible for this yield growth was apparently completely ineffective in low-yield, high-stress environments.     

Simulation of rice planthopper damage for developing pest management decision support tools

Rice planthoppers' damage on Pusa Basmati 1 cultivar was simulated with InfoCrop, a generic crop growth simulation model. The model was calibrated and validated with two experimental data sets on planthopper population and rice yield that were generated through differential insecticide application during the rainy season 2006 and 2007. Simulated yield and total dry matter (TDM) in various treatments over the two experiments were found to be proximal to the observed yields (R² = 0.972, RMSE = 4.61%) and TDM (R² = 0.949, RMSE = 3.25%), respectively. Likewise, the simulated yield and TDM losses were also respectively close to observed yield losses (R² = 0.938, RMSE = 13.53%) and TDM losses (R² = 0.835, RMSE = 19.12%), suggesting appropriate validation of planthopper damage mechanism on Pusa Basmati 1 rice. Economic injury levels (EILs) of planthoppers were simulated with two control expenditures involving two applications with each of monocrotophos and imidacloprid, and three market prices of Pusa Basamti 1 rice. The EIL exhibited a negative relationship with market value of produce but a positive one with expenditure on control measures. Simulated EILs were comparable to earlier established empirical EILs, indicating utility of simulation models for developing location specific EILs that may help in doing away with the use of blanket EILs. Iso-loss curves, devised through validated model, depicted combinations of crop age and planthopper population that resulted in similar yield losses. Both the EILs and iso-loss curves can be useful in monitoring planthopper populations and promoting judicious pesticide applications that would avoid unwarranted control expenditure and environmental contamination. The simulation models being based on detailed crop ecological and physiological processes and pest damage mechanism can thus aid in development of location-specific decision support tools and ensure precision in pest management decisions.     

Water and nitrogen balance of sweet sorghum (Sorghum bicolor moench (L.)) cv. Keller under semi-arid conditions

In the framework of the E.U. project Fair CT 96-1913 “Environmental studies on sweet and fibre sorghum, sustainable crops for biomass and energy”, a research has been carried out with the aim to study the water and nitrogen balance and determine the critical N dilution curve of sweet sorghum cv. Keller. A field experiment was performed, where three irrigation treatments (I₀ = dry control, I₅₀ = 50% ETm restoration, I₁₀₀ = 100% ETm restoration) and four nitrogen fertilization levels (N₀ = no nitrogen control, N₆₀ = 60 kg ha⁻¹, N₁₂₀ = 120 kg ha⁻¹; N₁₈₀ = 180 kg ha⁻¹) were studied. The final yield was significantly affected by the amount of water distributed but not by the nitrogen level. The treatments watered up to crop establishment (I₀) produced, in the average, 7.5 t ha⁻¹ of dry matter, against 21.1 and 27.1 t ha⁻¹ of I₅₀ and I₁₀₀, respectively. The crop determined a great reduction in nitrate concentration of soil water, irrespective of nitrogen supplied. The variation between N output and input (Δ) was negative in N₀, N₆₀ and N₁₂₀ and positive in N₁₈₀. The critical value of nitrogen uptake change in relation to the water availability. The amount of nitrogen supplied did not determine significant differences upon WUE. The crop seems to have a great potentiality in Mediterranean environment in terms of yield production.     

Quantification of the cardinal temperatures and thermal time requirement of opium poppy (Papaver somniferum L.) seeds to germinate using non-linear regression models

The response of plant development rate (including germination rate) to temperature might be described as a non-linear function. We compared 3 non-linear regression models (Dent-like, segmented and beta) to describe the germination rate-temperature relationships of opium poppy (Papaver somniferum L.) over 6 constant temperatures to find cardinal temperatures and thermal time required to reach different germination percentiles. Two replicated experiments were performed with the same temperatures. An iterative optimization method was used to calibrate the models and different statistical indices (mean absolute error, coefficient of determination (R²), intercept and slope of the regression equation of predicted vs. observed germination rate) were applied to compare their performance. The segmented was found to be the best model to predict germination rate (R² = 0.92, MAE = 0.0011 and CV of 1.4-3.6%). Estimated cardinal temperatures were similar for different germination percentiles (P < 0.05). Base on the model outputs, the base, the optimum and the maximum temperatures for germination were estimated as 3.02, 27.36 and 36.31 °C. The thermal time required to reach 50 and 95% germination was 57.27 and 87.55 degree-days, respectively. Model predictions of the time required for seed germination agreed reasonably well with the observed times (MAE = 0.56 day, R² = 0.887). All model parameters may be readily used in crop simulation models.     

Sweet sorghum productivity for biofuels under increased soil salinity and reduced irrigation

Sweet sorghum (Sorghum bicolor (L.) Moench.) is a drought-tolerant crop with high resistance to saline-alkaline soils, and sweet sorghum may serve as an alternative summer crop for biofuel production in areas where irrigation water is limited. A two-year study was conducted in Northern Greece to assess the productivity (biomass, juice, total sugar and theoretical ethanol yields) of four sweet sorghum cultivars (Sugar graze, M-81E, Urja and Topper-76-6), one grain sorghum cultivar (KN-300) and one grass sorghum cultivar (Susu) grown in intermediate (3.2 dS m⁻¹) or in high (6.9 dS m⁻¹) soil salinity with either low (120 mm) or intermediate (210 mm) irrigation water supply (supplemented with 142–261 mm of rainfall during growth). The soil salinity and irrigation water supply effects on the sorghum chlorophyll content index, photosystem II quantum yield, stomatal conductance and leaf K/Na ratio were also determined. The sorghum emergence averaged 75,083 plants ha⁻¹ and 59,917 plants ha⁻¹ in a soil salinity of 3.2 dS m⁻¹ and 6.9 dS m⁻¹, respectively. The most affected cultivar, as averaged across the two soil salinity levels, was the Susu grass sorghum emerging at 53,250 plants ha⁻¹, followed by the Topper-76-6 sweet sorghum emerging at 61,250 plants ha⁻¹. The leaf K/Na ratio decreased with decreasing irrigation water supply, in most cases, but it was not significantly affected by soil salinity. The dry biomass, juice and total sugar yields of sorghum that received 210 mm of irrigation water was 49–88% greater than the yields of sorghum that received the 120 mm of irrigation water. Sorghum plants grown in a soil salinity of 3.2 dS m⁻¹ produced 42–58% greater dry biomass, juice and total sugar yields than the yields of sorghum plants grown in a soil salinity of 6.9 dS m⁻¹. The greatest theoretical ethanol yield was produced by sweet sorghum plants grown in a soil salinity of 3.2 dS m⁻¹ with 210 mm of irrigation water (6130 L ha⁻¹, as averaged across cultivar), and the Urja and Sugar graze cultivars produced the most ethanol (7620 L ha⁻¹ and 6528 L ha⁻¹, respectively). Conclusively, sweet sorghum provided sufficient juice, total sugar and ethanol yields in fields with a soil salinity of 3.2 dS m⁻¹, even if the plants received 50–75% of the irrigation water typically applied to sorghum.     

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.     

Relationships involving several types of extractives of five native argentine wood species of genera Prosopis and Acacia

The relationships existing among the values obtained when extracting the wood of four Argentinean species of Prosopis (P. alba, P. kuntzei, P. nigra, and P. ruscifolia) and one of the Acacia (A. aroma) by several procedures were evaluated and discussed. The used methods were: extraction in toluene/ethanol and hot water; determination of tannic and non-tannic content; measurement of phenolic compounds. Additionally, liquid chromatography (HPLC) was also used in order to quantitatively evaluate the content of (−)-mesquitol, a relatively unusual flavonoid (flavanol type). The total amount of Oxidation Products was also measured. They result from oxidation and polymerization processes of phenolic compounds occurring during heartwood formation, and were not separated during chromatographic analysis. Data evidenced a linear trend (R² = 0.970) between organic and tannic extractives of all species, and a similar one (R² = 0.927) between total phenols and tannic (or organic) extractives in the case of heartwood of Prosopis species. Interestingly, for sapwood very different values of organic extracts, tannic content or Oxidation Products type compounds were measured in spite of a similar amount of phenolic substances. Moreover, the various species presented the same peaks in chromatograms, thus evidencing the chemical similarity of compounds but a different quantity between heartwood and sapwood and also among the various species. The observed similarity implied that the various methods of extraction did not really extract only a single class of substances, and that great care must be adopted when using some specific procedures for extractions.Furthermore, the existing relationships between extractives and selected technological properties, namely specific volumetric shrinkage coefficient (BSvol) and natural durability (evaluated in terms of mass loss after fungal attacks in laboratory conditions), were given. It appeared that in heartwood BSvol was well correlated to organic extractives (R² = 0.984), thus evidencing the microimpregnation of cell walls by extractives, but the fitting quality of the correlation was dependent on the type of extractives used. Analogously, a good relationship between mass loss and phenolic compounds existed (R² = 0.764), and in this case the value of R² was even more dependent on the considered extracts. Moreover, the availability of quantitative data on several Prosopis species allowed to consistently evaluate the bioactivity of (−)-mesquitol on the resistance against fungal attack, and the logarithmic form of the relationship between mass loss and (−)-mesquitol content suggested a direct fungicidal activity of this compound. On the other hand, data also evidenced that neither phenolic compounds nor (−)-mesquitol can be considered as the unique and definite factor able to determine the durability of the considered species.     

Mineral fertilizer response and nutrient use efficiencies of East African highland banana (Musa spp., AAA-EAHB,cv. Kisansa)

Poor yields of East African highland bananas (Musa spp., AAA-EAHB) on smallholder farms have often been attributed to problems of poor soil fertility. We measured the effects of mineral fertilizers on crop performance at two sites over two to three crop cycles; Kawanda in central Uganda and Ntungamo in southwest Uganda. Fertilizers were applied at rates of 0N–50P–600K, 150N–50P–600K, 400N–0P–600K, 400N–50P–0K, 400N–50P–250K and 400N–50P–600K kg ha⁻¹ yr⁻¹. In addition 60Mg–6Zn–0.5Mo–1B kg ha⁻¹ yr⁻¹ was applied to all treatments, with the exception of the control plots which received no fertilizer. Fresh bunch mass and yield increased with successive cycles. Yield increases above the control ranged from 3.1 to 6.2 kg bunch⁻¹ (average bunch weight for all treatments 11.5 kg bunch⁻¹) and 2.2–11.2 Mg ha⁻¹ yr⁻¹ (average yield for all treatments 15.8 Mg ha⁻¹ yr⁻¹) at Kawanda, compared with 12.4–16.0 kg bunch⁻¹ (average bunch weight for all treatments 14.7 kg bunch⁻¹) and 7.0–29.5 Mg ha⁻¹ yr⁻¹ (average yield for all treatments 17.9 Mg ha⁻¹ yr⁻¹) at Ntungamo. The limiting nutrients at both sites were in the order K > P > N. Potassium, N and P foliar nutrient mass fractions were below previously established Diagnosis and Recommendation Integrated System (DRIS) norms, with the smallest K mass fractions observed in the best yielding plots at Ntungamo. Total nutrient uptakes (K > N > P) were higher at Ntungamo as compared with Kawanda, probably due to better soil moisture availability and root exploration of the soil. Average N, P and K conversion efficiencies for two crop cycles at both sites amounted to 49.2 kg finger DM kg⁻¹ N, 587 kg finger DM kg⁻¹ P and 10.8 kg finger DM kg⁻¹ K. Calibration results of the model QUEFTS using data from Ntungamo were reasonable (R² = 0.57, RMSE = 648 kg ha⁻¹). Using the measured soil chemical properties and yield data from an experiment at Mbarara in southwest Uganda, the calibrated QUEFTS model predicted yields well (R² = 0.68, RMSE = 562 kg ha⁻¹). We conclude that banana yields can be increased by use of mineral fertilizers, but fertilizer recovery efficiencies need to improve substantially before promoting wide-scale adoption.     

Ecophysiological determinants of biomass and grain yield of wheat under P deficiency

Grain yield of crops can be expressed as a function of the intercepted radiation, the radiation use efficiency and the partitioning of above-ground biomass to grain yield (harvest index). When a wheat crop is grown under P deficiency the grain yield is reduced but it is not clear how these three components are affected. Our aim was (i) to identify which of these components were affected in spring bread wheat under P deficiency at field conditions and (ii) to relate the grain yield responses to processes of grain yield formation during the spike growth period. Three field experiments were conducted in the potentially high wheat yielding environment of southern Chile. All experiments had two levels of P availability: with (155 kg P ha⁻¹) or without P fertilization (average soil P-Olsen concentration of 10 ppm, a medium level of P availability). High wheat grain yields were obtained varying between 815 and 1222 g m⁻² with P applications. Experiments showed a grain yield reduction caused by P deficiencies of 35, 16 and 18% in experiments 1, 2 and 3, respectively. This was related (R² = 0.99, P < 0.01) to a reduction in the total above-ground biomass at harvest and not to the harvest index. Reductions in above-ground biomass were due to a reduction in radiation intercepted under P deficiency without effecting radiation use efficiency. Grain number per square meter was the main yield component (R² = 0.99, P < 0.01) that explained the grain yield reduction caused by the P deficiency which was due to low spike biomass at anthesis (R² = 0.96, P < 0.05). The reduction in spike biomass at anthesis was related (R² = 0.86, P < 0.01) to reductions in crop growth rate during the spike growth period as a consequence of a lower radiation intercepted during this period. This study showed that under high wheat yield conditions the main effect of a P deficiency on grain yield reduction was a negative impact on the total above-ground biomass due to the negative impact on intercepted radiation, particularly during the spike growth period, affecting negatively spike biomass at anthesis and consequently grain number and yield.     

Al toxicity effects on radiation interception and radiation use efficiency of Al-tolerant and Al-sensitive wheat cultivars under field conditions

Soil acidity and Al toxicity are highly extended in agricultural lands of Chile, especially where wheat is widely sown. To evaluate quantitatively the response of wheat biomass and its physiological determinants (intercepted radiation and radiation use efficiency) to Al toxicity, two field experiments were conducted in an Andisol in Valdivia (39°47′S, 73°14′W), Chile, during the 2005–2006 and 2006–2007 growing seasons. Treatments consisted of a factorial arrangement of: (i) two spring wheat cultivars with different sensitivity to Al toxicity (the sensitive cultivar: Domo.INIA and the tolerant cultivar: Dalcahue.INIA) and (ii) five exchangeable Al levels (from 0 to 2.7 cmol₍₊₎ kg⁻¹) with three replicates. Crop phenology and intercepted radiation (IR) were registered during the entire crop cycle, while 10 samples of above-ground biomass were taken at different stages between double ridge and maturity. Both biomass and leaf area index (LAI) were recorded in these 10 stages. Radiation use efficiency (RUE) was calculated as the slope of the relationship between accumulated above-ground biomass and accumulated photosynthetically active radiation intercepted by the canopy (IPARa). Crop phenology was little affected by soil Al treatments, showing only up to 17 days delay in the Al-sensitive cultivar under extreme Al treatments. Above-ground biomass at harvest was closely associated (R² = 0.92) with the crop growth rate but no relationship (R² = 0.14) was found between the crop cycle length. IPARa explained almost completely (R² = 0.93) the above-ground biomass reached by the crop at harvest under the wide range of soil Al concentrations explored in both experiments. On the other hand, a weaker relationship was found between above-ground biomass and RUE. The effect of soil Al concentration on IPARa was mainly explained by LAI as a single relationship (R² = 0.93) between IR (%) and LAI at maximum radiation interception showing a common light attenuation coefficient (k = 0.33).     

Uptake and use efficiency of N, P, K, Ca and Al by Al-sensitive and Al-tolerant cultivars of wheat under a wide range of soil Al concentrations

The impacts of acidic soils and Al toxicity on wheat nutrient economy have been scarcely researched under field conditions even though these soils are widely spread in wheat production areas around the world. The main objective of this study was to quantitatively evaluate the element (N, P, K, Ca and Al) economy of an Al-sensitive and an Al-tolerant wheat cultivar growing under different soil Al concentrations at field conditions. To reach this objective, two field experiments were conducted in an Andisol in Valdivia (39°47′18″S, 73°14′05″W), Chile. Treatments were a factorial arrangement of: (i) two spring wheat cultivars (Al-sensitive, Domo.INIA and Al-tolerant, Dalcahue.INIA) and (ii) five exchangeable Al levels (0-2.7 cmol₍₊₎ kg⁻¹) with three replicates. At harvest, plant biomass was sampled and divided into 5 organ categories: ears, grains, blade leaves, stems plus sheath leaves and roots. The element content (N, P, K, Ca and Al) in each organ was measured to quantify element uptake and concentration, nutrient uptake efficiency (UPE) and nutrient utilization efficiency (UTE). Element uptake (N, P, K, Ca, and Al) was negatively affected by the increased soil Al concentration in above-ground and root biomass in both cultivars (R² = 0.61-0.98, p < 0.01), although clear differences were found between cultivars. On the contrary, the impact of soil exchangeable Al on the plant element concentration was minor, showing weak associations with soil Al levels. However, the Al concentration in above-ground tissues of the Al-sensitive cultivar was an exception because it increased exponentially with the Al soil concentration (R² = 0.96-0.99, p < 0.001). Nutrient uptake efficiencies, UPEs (N, P, K and Ca), were negatively affected by soil Al concentrations and were well described by linear equations in both cultivars (R² = 0.58-0.98, p < 0.05), with notable differences between them. Both nutrient uptake (capture) and UPE were the traits that best explained above-ground biomass production (R² = 0.82-0.99, p < 0.001, n = 20). Nutrient utilization efficiency, UTEs (N, P, K and Ca) responded more conservatively to the soil Al concentration, except for the Al sensitive cultivar under very high soil Al levels.     

Analysis of host plant resistance to multiple Fusarium species associated with stalk rot disease in sorghum [Sorghum bicolor (L.) Moench]

Fusarium spp. is among the largest and most important pathogen groups that attack major grain crops including sorghum. The objectives of this study were to compare the virulence of Fusarium spp. associated with sorghum and examine the mode of resistance of genotypes to the disease. Eight Fusarium species – F. verticillioides, F. thapsinum, F. andiyazi, F. proliferatum, F. nyagamai, F. pseudoanthophilum, F. brevicatenulatum, and F. pseudonygamai – were studied using three sorghum genotypes under greenhouse condition. Three of these pathogens (F. verticillioides, F. thapsinum, and F. andiyazi) were selected for genetic analysis of resistance under field conditions. Sorghum genotypes with contrasting stalk rot reactions were selected for use in both the greenhouse and field experiments. Two weeks after flowering, plants were inoculated with liquid inoculum culture (5 × 10⁴ conidia ml⁻¹) of the different pathogens. Plants were harvested 4 weeks after inoculation and rated for disease severity on the basis of lesion length and number of nodes crossed by the lesion. Among the pathogens, F. thapsinum resulted in consistently higher disease scores in all genotypes under all environments. Likewise, genotype SC599 showed the greatest and most stable resistance as inbred as well as in hybrid combinations as shown by consistently high GCA for resistance to all pathogen species. We recommend that future screening exercises for Fusarium stalk rot resistance utilize F. thapsinum as the causal organism and include the resistant genotype SC599 as a control.     

Evaluating cultivars in unbalanced on-farm participatory trials

Data from on-farm participatory varietal trials are often highly unbalanced. Using statistically robust techniques we showed that such data are amenable to sophisticated analyses. Data from 38 varieties of wheat tested in 44 mother trials (all test varieties compared) and 663 baby trials (single entries compared with local checks) over 6 years in Lunawada, Gujarat, India, were analysed. Two combined analyses for grain yield were performed by using either a fixed effects model within general linear modelling (GLM) or a mixed effects model using the restricted maximum likelihood (REML) procedure. Both analyses made substantial adjustments over the raw means and the estimated mean values from the two analyses for the fixed set of tested varieties were highly correlated (R² = 0.89) as were the t-value that compared test cultivars with the check variety (R² = 0.96). The GLM detected 15 varieties and REML detected 12 varieties that were significantly superior to the check cultivar with 11 varieties in common. Both methods were similar in identifying the top-most promising varieties but REML was more conservative (i.e. more subject to Type II error) with larger standard errors (S.E.s) of variety means for n > 17. However, for both procedures the S.E.s increased sharply when the number of trials decreased below 17.     

SSR-based and grain yield-based diversity of hybrid maize in Thailand

Commercial hybrid maize varieties are often used to extract new inbred lines in hybrid breeding programs. Seven commercial hybrid maize varieties were crossed in a diallel design, and the resulting hybrids and selfed progeny were evaluated for yield and adaptability grown in six locations in Thailand. The parental varieties were analyzed with a set of 64 Simple Sequence Repeat (SSR) loci, spanning all 10 chromosomes. The average number of alleles per SSR locus was 4.98 with a range of 2–11. The polymorphic information content (PIC) varied from 0.24 to 0.89, with an average of 0.69. Using SSR-based genetic distance (GD), an UPGMA dendrogram showed seven field corn varieties classified into three distinct groups. Troyer's genetic distance (TGD) calculated from yield data, which is a function of inbreeding depression, varied from 0.493 to 1.015 between different parental combinations. A significant positive correlation was found between the GD and TGD across the six locations (0.66^**). The GD correlated positively with specific combining ability (SCA) as well across all locations (r = 0.76^**) heterosis was significant for grain yield and SCA, accounting for 47% of the sum of the square among entries. Therefore, we suggest that broad base populations derived from each of the distinct groups can be formed using combined criteria of SSR-based GD, TGD, grain yield, GCA and SCA.