Adaptation strategy,germplasm type and adaptive traits for field pea improvement in Italy based on variety responses across climatically contrasting environments

A pea breeding strategy is required to cope with the large climatic variation featuring south-European environments. Thirty-seven recent cultivars bred by 21 European or Australian institutions were grown in two climatically contrasting Italian sites (Lodi, subcontinental; Foggia, Mediterranean), two cropping years per site and two sowing times per year, to define various elements of this strategy. The study assessed: (i) the impact of genotype × environment (GE) interaction due to spatial and temporal factors on the consistency of top-yielding cultivars; (ii) the similarity between environments for GE effects and its implications on adaptation strategies; (iii) the extent of genotypic and GE interaction effects, and the relationship with adaptive responses, for various morphophysiological traits; (iv) the adaptation pattern and the combination of adaptive traits featuring three germplasm types, i.e. European spring and winter types, and germplasm selected in Mediterranean environments; (v) the predicted efficiency of direct and indirect selection procedures for grain yield. The geoclimatic area had a major impact on crop yield (5.15 t/ha in Lodi vs. 2.52 t/ha in Foggia) but tended to affect GE interaction less than time or year of autumn sowing, suggesting to breed for wide adaptation. Top-yielding cultivars as modeled by additive main effects and multiplicative interaction were environment-specific. On average, spring and winter materials outyielded the Mediterranean germplasm but the spring type, characterized by wide entry variation, included most widely- and specifically-adapted top-yielding cultivars. Cold-tolerant spring-type germplasm is preferable to breed for wide adaptation as it may combine high yield potential with adaptation to winter cold and terminal drought and heat stress. Lodging susceptibility, harvest index, onset and duration of flowering, and canopy height at maturity assessed in individual environments showed moderate to fairly high broad-sense heritability on a plot basis (h² > 0.20) and tended to correlation with yield over test environments (r ≥ 0.20). An indirect selection index including harvest index and canopy height exhibited about 20% greater predicted efficiency than direct selection for yield when using one selection environment and could be preferred for early selection stages. Direct yield selection in late selection stages should ideally be performed across 2 years in two environments that contrast for geoclimatic area and time of autumn sowing.     

Genotype × environment interaction for zinc and iron concentration of wheat grain in eastern Gangetic plains of India

Zinc and iron are important micronutrients for human health for which widespread deficiency occurs in many regions of the world including South Asia. Breeding efforts for enriching wheat grains with more zinc and iron are in progress in India, Pakistan and CIMMYT (International Maize and Wheat Improvement Centre). Further knowledge on genotype × environment interaction of these nutrients in the grain is expected to contribute to better understand the magnitude of this interaction and the potential identification of more stable genotypes for this trait. Elite lines from CIMMYT were evaluated in a multilocation trial in the eastern Gangetic plains (EGP) of India to determine genotype × environment (GE) interactions for agronomic and nutrient traits. Agronomic (yield and days to heading) data were available for 14 environments, while zinc and iron concentration of grains for 10 environments. Soil and meteorological data of each of the locations were also used. GE was significant for all the four traits. Locations showed contrasting response to grain iron and zinc. Compared to iron, zinc showed greater variation across locations. Maximum temperature was the major determinant for the four traits. Zinc content in 30–60 cm soil depth was also a significant determinant for grain zinc as well as iron concentration. The results suggest that the GE was substantial for grain iron and zinc and established varieties of eastern Gangetic plains India are not inferior to the CIMMYT germplasm tested. Hence, greater efforts taking care of GE interactions are needed to breed iron and zinc rich wheat lines.     

Adaptation,diversity, and exploitation of global white lupin (Lupinus albus L.) landrace genetic resources

White lupin requires grain yield improvement to realize its potential as a high-protein grain crop. Some 121 entries representing 13 germplasm pools (11 landrace pools from European countries and from regions of North and East Africa, West Asia and Atlantic islands, and one winter-type and one spring-type variety pools) were evaluated in three major agroclimatic conditions, i.e., Mediterranean and subcontinental climate in Italy under autumn sowing and suboceanic climate in France under spring sowing, with the aim to assess: (i) the variation among and within germplasm pools for grain yield and 13 major morphophysiological traits; (ii) the impact of evaluation environments on entry characteristics; and (iii) the relation of wide- and specific-adaptation responses with morphophysiological traits. Indications on top-yielding genetic resources, entry morphophysiological traits and association of these traits with grain yield were largely environment-specific. Germplasm pools summarized a fairly high portion of genotypic and genotype × environment (GE) interaction variation, indicating their usefulness as a criterion for locating genetic resources with specific characteristics. Adaptive responses of germplasm pools and individual entries, modeled through Additive Main effects and Multiplicative Interaction analysis, highlighted the outstanding agronomic value for specific agroclimatic conditions of a few landrace germplasm pools in comparison with variety pools. Overall within-pool diversity for morphophysiological traits and adaptive response was largest in the landrace pools from Italy, Turkey, East Africa and West Asia. Only flowering time and individual seed weight exhibited high genetic correlations between environments for entry response, suggesting caution in inferring accession characteristics from evaluation data obtained in environments very different from those targeted by possible germplasm users. Optimal flowering time was early in the spring-sown environment, intermediate in the Mediterranean environment, and late (associated with winter survival) in the subcontinental-climate environment. Owing to the association of phenology with several other traits, germplasm ordination for adaptation pattern and for overall morphophysiological variation were very similar. Pod fertility emerged among the seed yield components because of its correlation with grain yield in each environment combined with fairly low GE interaction. Beside contributing to the ecogeographic classification of landrace germplasm, our results can support breeding programs of Europe and Mediterranean-climate regions in defining useful genetic resources, adaptation strategies and adaptive traits. Genetic resources from Madeira & Canaries (high-yielding across environments), Italy (featuring high adaptive and morphophysiological diversity) and a few other regions are of special interest for breeding in targeted definite agroclimatic conditions.     

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.     

Evaluation of early to medium maturing open pollinated maize varieties in SADC region using GGE biplot based on the SREG model

Analysis of multi-environment trials (METs) of genotypes (G) and genotype × environment (GE) interactions for yield performance across environments, and selection of the best genotypes is an important routine in maize breeding programs. Analysis and interpretation of METs data have been limited to analysis of variance and mean comparison among genotypes. This type of analysis has not been effective in exploiting GE interactions encountered in METs data sets. The objectives of this study were to exploit METs data sets from maize regional trails using G plus GE interaction (GGE) biplot based on the site regression (SREG) model. The GGE biplots displays graphically the relationship among test environments, genotypes and GE interactions. Grain yield data of 35 early to medium maturing open pollinated maize varieties (OPVs) from five seasons (1999–2003) across 59 locations in Southern African Development Community (SADC) were analyzed. The GGE biplots based on the SREG model indicated that yield performance of maize OPVs were under major environments and of GE interactions. The construction of GGE biplots based on SREG model analysis showed the ideal test environments that discriminate well performing maize OPVs from poor ones, the performance of each OPV in specific year, the discrimativiness versus representativeness view of the GGE biplot of the test locations across the years, the relation among OPVs relative to grain yield, the stability of OPVs across environments and which OPVs is best for what.     

Interpretation of genotype × environment interactions of sugarcane: Identifying significant environmental factors

An understanding of the causes of genotype × environment (G × E) interactions is essential for the implementation of efficient selection and evaluation networks. Currently, studies involving the interpretation of sugarcane (Saccharum spp.) G × E interactions are limited. The objective of this study was to investigate the relative influence of environmental factors on the G × E interactions of sugarcane under rainfed conditions in South Africa through a comprehensive analysis of a multi-environment trial (MET) dataset. Fifteen commercial cultivars were evaluated over 147 environments (trial × ratoon combinations) across the coastal (C), hinterland (H) and midlands (M) regions of the sugar industry. Environments were characterized according to five site covariates (soil depth, clay percentage, organic matter percentage, nitrogen mineralization category, and total available moisture) and nine seasonal covariates (time of harvest, age at harvest, average daily heat units, solar radiation, rainfall, evaporation, and three derived water stress indices).Additive main effects and multiplicative interaction (AMMI) biplots for cane yield (TCANE), estimated recoverable crystal percent (ERC) and tons ERC (TERC) revealed overlapping of C and H environments, while M environments formed unique clusters characterized by specific cultivar adaptabilities. Principal components analysis (PCA) allowed visualization of the covariates determining the regional separation patterns. AMMI interaction principal components axes (IPCA) 1 and 2 scores were correlated to the covariates and showed that harvest age, temperature, and water stress were mainly responsible for separation of M environments from C and H environments on the TCANE and TERC biplots. Time of harvest was identified as an important covariate influencing ERC G × E patterns in the C and H regions. The third water stress index (based on a ratio of observed yields to simulated irrigated yields) was a dominant factor influencing G × E patterns within the C and H regions and was identified as a superior indicator of water deficient environments for future studies. The M trials were characterized by shallower soils with lower total available moisture and greater variability in this regard compared with the C and H trials. Nitrogen mineralization category, organic matter percent, and clay percent were not significantly correlated to IPCA scores, while soil depth was identified as a major site selection criterion in the M region. The M region should be treated as a single mega-environment, while the C and H regions could be combined for future interpretive studies, where covariates should be summarized within growth phases. The results of this study will assist in restructuring the MET network through exploitation and targeting of the relevant environmental factors within the different regions.     

Lucerne shoot and root traits associated with adaptation to favourable or drought-stress environments and to contrasting soil types

Cultivar × location interaction for lucerne forage yield across northern Italy is large, repeatable and associated with summer drought-stress level and soil type. The objectives of this study were: (i) to investigate the genotypic factors associated with cultivar adaptive responses to drought-stress and soil factors; (ii) to identify adaptive traits exploitable for selection of widely adapted or specifically adapted material. Aerial dry matter (DM) over 12 harvests and shoot traits of 13 landraces and four varieties were evaluated in four artificial environments created by the factorial combination of drought-stress level (almost nil or high) and soil type (sandy-loam or silty-clay) (Exp. 1). Aerial and root DM over four or five harvests were evaluated in metal containers 55 cm × 12 cm × 75 cm deep for the factorial combinations of three varieties by two drought-stress levels by two soil types (Exp. 2), or six landraces by two drought-stress levels (Exp. 3). Cultivar × environment interaction was detected for forage yield, plant mortality after the second summer, leaflet size and stem weight. The environments of Exp. 1 reproduced well the variety adaptive responses across agricultural environments. The relationship of cultivar forage yield with shoot traits was environment-specific, i.e.: (i) strictly negative with plant mortality, in no-stress environments (where mortality and plant competition were severe); (ii) positive with stem number per plant and autumn-winter growth, in stress environments; (iii) positive with stem dry weight, in ‘stress/sandy-loam soil’; and (iv) positive with leaflet size, in ‘no-stress/sandy-loam soil’. Cultivars specifically adapted to no-stress or sandy-loam conditions showed consistently greater root DM across three soil layers than material with opposite adaptive response. Entry yields tended to inverse genetic correlation between two environments which represented contrasting geographical subregions and were characterized by different combinations of traits associated with higher yield, i.e.: (i) higher root biomass, lower plant mortality and larger leaflets, for ‘no-stress/sandy-loam soil’; and (ii) more stems per plant and greater autumn-winter growth, for ‘stress/silty-clay soil’. The difficulty of yield-based selection for wide adaptation may hardly be overcome by selection based on adaptive traits. Adaptive trait-based selection for specific adaptation may be envisaged especially for ‘stress/silty-clay soil’ conditions, for which the relevant traits are inexpensive to record, not correlated, and not subject to cultivar × environment interaction.     

Multiple-disease resistance in Vicia faba: Multi-environment field testing for identification of combined resistance to rust and chocolate spot

The aim of this work was to identify Vicia faba germplasm resistant both to rust and chocolate spot. A collection of 43 accessions of V. faba previously identified as chocolate-spot resistant was evaluated for rust and chocolate spot resistance in Egypt and in Spain. The genotype and genotype × environment (GGE) biplot analyses allowed the selection of 11 accessions resistant to both diseases in those locations. These 11 accessions were evaluated for rust in an additional field trial in Spain, all performing better than the susceptible check. The joint analysis of the 11 accessions in the four field trials where they had been evaluated revealed no significant effects either for genotype, environment or the genotype × environment interaction. They are hence promising sources of resistance, both for their low severities and their stable responses across the studied environments. This collection was also tested under controlled conditions against the Egyptian and the Spanish isolates of rust present in the field trials further underlining the stable performance of these genotypes. Finally, the effect of previous infection with chocolate spot on rust resistance was assessed under controlled conditions and no influence of it was found.     

Response of common wheat varieties to organic and conventional production systems across Italian locations,and implications for selection

Specific breeding for organic systems may help reduce their yield gap relative to conventional systems by exploiting genotype × system (GS) interaction. Likewise, specific breeding for distinct subregions within a region could capitalize on genotype × location (GL) interaction. Grain yield and test weight of common wheat varieties were evaluated under organic and conventional systems in ten locations spanning from northern to southern Italy, with the objectives of: (i) comparing production systems; (ii) investigating the extent of GS and GL interactions and their relationship with genotypic and environmental characteristics; and (iii) preliminarily comparing, in terms of predicted selection gains, different strategies to cope with GS and GL effects. These effects were investigated in the 2-year Data set 1 including seven genotypes. GS effects were also assessed in the annual Data sets 2 and 3 including 13 and 11 genotypes, respectively. The yield reduction of organic systems relative to conventional ones averaged 28% in Data set 1, 29% in Data set 2 and 14% in Data set 3. Organic systems also tended to a modest test weight reduction. Genetic correlations between systems ranged from high to very high (0.88 ≤ r_g ≤ 0.98) for yield and test weight, owing to nil or limited GS interaction. Broad-sense heritability tended to be higher in conventional systems than organic ones for yield in two data sets (mainly due to lower experimental error) while being similar in the two systems in the other cases. Predicted selection gains suggested nil (yield) or very modest (test weight) advantage of direct selection in organic systems relative to indirect selection in conventional systems, when targeting organic systems. The scope for selection only in conventional systems was reinforced when comparing predicted gains for selection scenarios which target both systems in relation to their foreseeable marketing importance. GL effects for yield and test weight were significant and were modeled by additive main effects and multiplicative interaction analysis. Site classification based on GL effects for yield revealed a larger subregion A including northern and central Italy and a smaller subregion B comprising southern Italy, accordingly with previous, independent studies. Yield selection only in subregion A (with indirect selection gain for subregion B) implied slightly higher predicted gain for A (+4%) and much lower gain for B (−24%) relative to independent, direct selection in each subregion. Selection for specific geoclimatic subregions may have greater importance than selection for specific production systems.     

High-yield irrigated maize in the Western U.S. Corn Belt: II. Irrigation management and crop water productivity

Appropriate benchmarks for water productivity (WP), defined here as the amount of grain yield produced per unit of water supply, are needed to help identify and diagnose inefficiencies in crop production and water management in irrigated systems. Such analysis is lacking for maize in the Western U.S. Corn Belt where irrigated production represents 58% of total maize output. The objective of this paper was to quantify WP and identify opportunities to increase it in irrigated maize systems of central Nebraska. In the present study, a benchmark for maize WP was (i) developed from relationships between simulated yield and seasonal water supply (stored soil water and sowing-to-maturity rainfall plus irrigation) documented in a previous study; (ii) validated against actual data from crops grown with good management over a wide range of environments and water supply regimes (n = 123); and (iii) used to evaluate WP of farmer's fields in central Nebraska using a 3-y database (2005–2007) that included field-specific values for yield and applied irrigation (n = 777). The database was also used to quantify applied irrigation, irrigation water-use efficiency (IWUE; amount of yield produced per unit of applied irrigation), and the impact of agronomic practices on both parameters. Opportunities to improve irrigation management were evaluated using a maize simulation model in combination with actual weather records and detailed data on soil properties and crop management collected from a subset of fields (n = 123). The linear function derived from the relationship between simulated grain yield and seasonal water supply, namely the mean WP function (slope = 19.3 kg ha⁻¹ mm⁻¹; x-intercept = 100 mm), proved to be a robust benchmark for maize WP when compared with actual yield and water supply data. Average farmer's WP in central Nebraska was ∼73% of the WP derived from the slope of the mean WP function. A substantial number of fields (55% of total) had water supply in excess of that required to achieve yield potential (900 mm). Pivot irrigation (instead of surface irrigation) and conservation tillage in fields under soybean–maize rotation had the greatest IWUE and yield. Applied irrigation was 41 and 20% less under pivot and conservation tillage than under surface irrigation and conventional tillage, respectively. Simulation analysis showed that up to 32% of the annual water volume allocated to irrigated maize in the region could be saved with little yield penalty, by switching current surface systems to pivot, improving irrigation schedules to be more synchronous with crop water requirements and, as a fine-tune option, adopting limited irrigation.     

Evidence of varietal adaptation to organic farming systems

Consumer demand regarding the impacts of conventional agriculture on the environment and human health have spurred the growth of organic farming systems; however, organic agriculture is often criticized as low-yielding and unable to produce enough food to supply the world's population. Using wheat as a model crop species, we show that poorly adapted cultivars are partially responsible for the lower yields often found in organic farming systems when compared with conventional farming systems. Our results demonstrate that the highest yielding soft white winter wheat genotypes in conventional systems are not the highest yielding genotypes in organic systems. An analysis of variance for yield among 35 genotypes between paired organic and conventional systems showed highly significant (P < 0.001) genotype × system interactions in four of five locations. Genotypic ranking analysis using Spearman's rank correlation coefficient (R_S) showed no correlation between genotypic rankings for yield in four of five locations; however, the ranks were correlated for test weight at all five locations. This indicates that increasing yield in organic systems through breeding will require direct selection within organic systems rather than indirect selection in conventional systems. Direct selection in organic systems produced yields 15%, 7%, 31% and 5% higher than the yields resulting from indirect selection for locations 1–4, respectively. With crop cultivars bred in and adapted to the unique conditions inherent in organic systems, organic agriculture will be better able to realize its full potential as a high-yielding alternative to conventional agriculture.     

Dynamic patterns of components of genotype × environment interaction for pod yield of peanut over multiple years: A simulation approach

The relative importance of the genotype × year (G × Y), genotype × location (G × L) and genotype × location × year (G × L × Y) interactions has significant implications on the testing strategy of crop breeding lines. The goal of this study was to examine the dynamic patterns of these three interactions for pod yield of peanut using a crop simulation model. Pod yields of 17 peanut lines in the early-rainy, mid-rainy and dry seasons at 112 locations covering all peanut production areas in Thailand were simulated for 30 years (1972–2002) with the Cropping System Model (CSM)-CROPGRO-Peanut. Combined analyses of variance were preformed for individual seasons and for overall seasons, with the number of year incrementally increasing from 2 to 30, and the relative contributions of the individual sources of variation were determined. This procedure was repeated four times with different starting years. The results showed that the environmental effects accounted for the major proportion of the total yield variation, followed by the genotype effects, while the genotype × environment (G × E) effects were rather small. The contributions of the individual sources changed as the number of years in the analysis changed. Increasing number of years in the analyses resulted in an increase in the magnitude of the G × Y and G × L × Y interactions, but a decline in the G × L contribution. The contributions of the G × Y and G × L interactions were greater and more fluctuated in the dry season, while those of the G × L × Y interactions were greater in the mid-rainy season. Notable increases in the G × Y interaction in the dry season were observed in certain years. The decline in the G × L interaction with increasing number of years was closely associated with the increase in the G × L × Y interaction, and both became stable when 6 or more years were included. Several cross-over in the ranks of peanut lines for mean pod yield in two contrasting years were also observed for the mid-rainy season. These results raise a question on the effectiveness of the strategy for using locations to replace years in varietal testing that is normally employed by breeders. The practical limit of multi-year evaluation of crop breeding lines could be overcome by the use of a crop simulation model.     

Determinants of barley grain yield in a wide range of Mediterranean environments

Barley grain yield in rainfed Mediterranean regions can be largely influenced by terminal drought events. In this study the ecophysiological performance of the ‘Nure’ (winter) × ‘Tremois’ (spring) barley mapping population (118 Doubled Haploids, DHs) was evaluated in a multi-environment trial of eighteen site–year combinations across the Mediterranean Basin during two consecutive harvest years (2004 and 2005). Mean grain yield of sites ranged from 0.07 to 5.43 t ha⁻¹, clearly dependent upon both the total water input (rainfall plus irrigation) and the water stress index (WSI) accumulated during the growing season. All DHs were characterized for possessing molecular marker alleles tagging four genes that regulate barley cycle, i.e. Vrn-H1, Vrn-H2, Ppd-H2 and Eam6. Grain yield differences were initially interpreted in terms of mean differences between genotypes (G), environments (E), and for each combination of genotype and environment (GE) through a “full interaction” ANOVA model. Variance components estimates clearly showed the greater importance of GE over G, although both were much lower than E. Alternative linear and bilinear models of increasing complexity were used to describe GE. A linear model fitting allelic variation at the four genes explained genotype main effect and genotype × environment interaction much better than growth habit itself. Adaptation was primarily driven by the allelic constitution at three out of the four segregating major genes, i.e. Vrn-H1, Ppd-H2 and Eam6. In fact, the three genes together explained 47.2% of G and 26.3% of GE sum of squares. Grain yield performance was more determined by the number of grains per unit area than by the grain weight (phenotypic correlation across all genotypic values: r = 0.948 and 0.559, respectively). The inter-relationships among a series of characters defining grain yield and its components were also explored as a function of the length of the different barley developmental phases, i.e. vegetative, reproductive, and grain filling stages. In most environments, the best performing (adapted) genotypes were those with faster development until early occurrence of anthesis. This confirmed the crucial role of the period defining the number of grains per unit area in grain yield determination under Mediterranean environments.     

Genotype-by-environment interactions for grain yield associated with water availability at flowering in rainfed lowland rice

While a large genotype-by-environment (G × E) interaction component of variance for grain yield (GY) has been widely reported for rainfed lowland rice, the reasons for such large interactions are not well known. A random reference population of 34 genotypes taken from the Cambodian rice improvement program was used to examine the magnitude and nature of G × E interactions for GY in Cambodia. These genotypes were evaluated in a multi-environment trial (MET) conducted across 3 years (2000–2002) and eight locations in the rainfed lowlands. The G × E interaction was partitioned into components attributed to genotype-by-location (G × L), genotype-by-year (G × Y) and genotype-by-location-by-year (G × L × Y) interactions. The G × L × Y interaction was the largest component of variance for GY. The G × L interaction was also significant and comparable in size to the genotypic component (G). The significant G component was partly explained by a group of four genotypes that were broadly adapted to different environmental conditions represented by three environmental groups. The three environmental groups were identified from a pattern analysis, and the grouping was partly related to the time of sowing, and hence water availability at flowering. A major factor contributing to the large G × L × Y interactions for GY was late maturing genotypes being affected greatly when soil water availability at flowering was reduced greatly, compared to earlier maturing genotype groups. While the differential genotypic responses to the water availability environment explained part of a large G × E interaction for GY, other non-water related environmental conditions also appeared to have contributed to the interaction. Three target environments were identified for focusing efforts of the breeding programs in Cambodia, and four putative genotypes were selected for their high yield and wide adaptation in the rainfed lowlands.     

Yield response of corn to irrigation and nitrogen fertilization in a Mediterranean environment

Productivity and resource-use efficiency in corn (Zea mays L.) are crucial issues in sustainable agriculture, especially in high-demand resource crops such as corn. The aims of this research were to compare irrigation scheduling and nitrogen fertilization rates in corn, evaluating yield, water (WUE), irrigation water (IRRWUE) and nitrogen use (NUE) efficiencies. A 2-year field experiment was carried out in a Mediterranean coastal area of Central Italy (175 mm of rainfall in the corn-growing period) and corn was subjected to three irrigation levels (rainfed and supply at 50 and 100% of crop evapotranspiration, ETc) in interaction with three nitrogen fertilization levels (not fertilized, 15 and 30 g (N) m⁻²). The results indicated a large yearly variability, mainly due to a rainfall event at the silking stage in the first year; a significant irrigation effect was observed for all the variables under study, except for plant population. Nitrogen rates affected grain yield plant⁻¹ and ear⁻¹, grain and biomass yield, HI, WUE, IRRWUE and NUE, with significant differences between non-fertilized and the two fertilized treatments (15 and 30 g (N) m⁻²). Furthermore, deficit irrigation (50% of ETc) was to a large degree equal to 100% of the ETc irrigation regime. A significant interaction “N × I” was observed for grain yield and WUE. The effect of nitrogen availability was amplified at the maximum irrigation water regime. The relationships between grain yield and evapotranspiration showed basal ET, the amount necessary to start producing grain, of about 63 mm in the first and 206 mm in the second year. Rainfed crop depleted most of the water in the 0–0.6 m soil depth range, while irrigated scenarios absorbed soil water within the profile to a depth of 1.0 m. Corn in a Mediterranean area can be cultivated with acceptable yields while saving irrigation water and reducing nitrogen supply and also exploiting the positive interaction between these two factors, so maximizing resource-use efficiency.     

Analysis of starch swelling power in Australian breeding lines of hexaploid wheat (Triticum aestivum L.)

Starch is the major component of wheat (Triticum aestivum L.) grain and is composed of two large glucan molecules, amylose and amylopectin. The ratio between the two polymers types influences the water absorbing properties of starch upon heating, and thus affects the end-use of grain and purified starch. In this study, we evaluated the starch swelling power (SSP) values in seven wheat populations developed from crosses involving low-SSP lines. Analysis of starch produced by the F₂ generation plants showed that the largest SSP variation (11.4–16.2) and lowest SSP mean (13.9) was obtained for a population derived from doubled haploid lines SM1028 (SSP = 14.5) and VK306 (SSP = 13.6). The population of 360 lines was advanced by single seed descent to the following generations for further studies. Starch analysis of grain produced by F₄ generation lines in two field locations during 2006 and in a greenhouse environment during 2005 showed that SSP values were relatively stably inherited. The average broad-sense heritability was 73% and significant (P < 0.001) genotype × genotype and genotype × environment interactions were seen. Starches with the highest and lowest SSP values were inversely related to amylose concentration determined by high pressure liquid chromatography (HPLC)–size exclusion chromatography (SEC) of debranched starch. Developed lines with the lowest SSP values surpassed 40% in apparent amylose concentration. The study illustrates that screening for SSP in early generations can be used to develop wheat lines with desired starch swelling characteristics.     

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.     

Phytate and mineral elements concentration in a collection of Italian durum wheat cultivars

Mineral deficiencies are prevalent in human populations and the improvement of the mineral content in cereal products represents a possible strategy to increase the human mineral intake. Nevertheless, most of the inorganic phosphorus (P_i) present in mature cereal seeds (40–80%) is stored as phytate, an anti-nutritional factor that forms complexes with minerals such as Ca, Mg, Zn and Fe reducing their bioavailability. The present study was undertaken: (i) to determine the variation in phytate and mineral concentrations in the whole grains of 84 Italian durum wheat (Triticum durum Desf.) cultivars representative of old and modern germplasm; (ii) to estimate the magnitude of genotype × environment interaction effects; and (iii) to examine the interrelationships among mineral concentrations in durum wheat with the final aim to identify superior durum wheat cultivars that possess low phytate content and high concentration of mineral elements in their whole-wheat flour. The cultivars were grown in field trials during 2004–2005 at Foggia, Italy and during 2005–2006 at Foggia and Fiorenzuola d’Arda—Southern and Northern Italy. The phytate content was estimated indirectly by using a microtitre plate assay evaluating the P_i absorbance at 820 nm, while the Cu, Fe, Mn, Ca, K, Mg, Na and Zn mineral contents were determined by ICP/OES. The contents of Zn and Fe across years and locations ranged from 28.5 to 46.3 mg/kg for Zn with an average of 37.4 mg/kg and from 33.6 to 65.6 mg/kg for Fe with an average of 49.6 mg/kg. P_i grain content was between 0.46 and 0.76 mg/g showing a positive correlation with all minerals except Cu and Zn. Although breeding activity for Fe and Zn would be difficult because G × E interaction is prevalent, multi-location evaluation of germplasm collection help to identify superior genotypes to achieve this objective. The results here reported open the possibility of designing a specific breeding program for improving the nutritional value of durum wheat through the identification of parental lines with low-P_i and high minerals concentration in whole grains.     

Morphological characteristics and composition of lipophilic extractives and lignin in Brazilian woods from different eucalypt hybrids

The morphological and chemical characteristics of the woods from several eucalypt hybrids from the Brazilian Genolyptus program were studied. The hybrids selected for this study were Eucalyptus grandis × E. urophylla (IP), E. urophylla × E. urophylla (U1 × U2), E. grandis × [E. urophylla × E. globulus] (G1 × UGL), and [E. dunnii × E. grandis] × E. urophylla (DG × U2). The analyses of the lipophilic extractives indicated a similar composition in all eucalypt hybrids, which were dominated by sitosterol, sitosterol esters and sitosteryl 3β-d-glucopyranoside. These compounds are responsible for pitch deposition during kraft pulping of eucalypt wood. Some quantitative differences were found in the abundances of different lipid classes, the wood from U1 × U2 having the lowest amounts of these pitch-forming compounds. The chemical composition and structure of lignins were characterized by Py-GC/MS and 2D-NMR that confirmed the predominance of syringyl over guaiacyl units and only showed traces of p-hydroxyphenyl units in all the woods, with the highest S/G ratio for G1 × UGL. The 2D-NMR spectra gave additional information about the inter-unit linkages in the lignin polymer. All the lignins showed a predominance of β-O-4′ ether linkages (75-79% of total side-chains), followed by β-β′ resinol-type linkages (9-11%) and lower amounts of β-5′ phenylcoumaran-type, β-1′ spirodienone-type linkages or β-1′ open substructures. The lignin from the hybrid G1 × UGL presented also the highest proportion of β-O-4′ linkages, and therefore, it is foreseen that the wood from this hybrid will be more easily delignifiable than the other selected Brazilian eucalypt hybrids. In complement to these chemical analyses, the morphological characterization of fibers, vessels and fines revealed that hybrid eucalypt clone DG × U2 presented the most interesting properties for the manufacture of paper pulps and biofuels.     

Effect of water management on dry seeded and puddled transplanted rice: Part 2: Water balance and water productivity

Labour and water scarcity in north west India are driving researchers and farmers to find alternative management strategies that will increase water productivity and reduce labour requirement while maintaining or increasing land productivity. A field experiment was done in Punjab, India, in 2008 and 2009 to compare water balance components and water productivity of dry seeded rice (DSR) and puddled transplanted rice (PTR). There were four irrigation schedules based on soil water tension (SWT) ranging from saturation (daily irrigation) to alternate wetting drying (AWD) with irrigation thresholds of 20, 40 and 70 kPa at 18–20 cm soil depth. There were large and significant declines in irrigation water input with AWD compared to daily irrigation in both establishment methods. The irrigation water savings were mainly due to reduced deep drainage, seepage and runoff, and to reduced ET in DSR. Within each irrigation treatment, deep drainage was much higher in DSR than in PTR, and more so in the second year (i.e. after 2 years without puddling). The irrigation input to daily irrigated DSR was similar to or higher than to daily irrigated PTR. However, within each AWD treatment, the irrigation input to DSR was less than to PTR, due to reduced seepage and runoff, mainly because all PTR treatments were continuously flooded for 2 weeks after transplanting. There was 30–50% irrigation water saving in DSR-20 kPa compared with PTR-20 kPa due to reduced seepage and runoff, which more than compensated for the increased deep drainage in DSR. Yields of PTR and DSR with daily irrigation and a 20 kPa irrigation threshold were similar each year. Thus irrigation and input water productivities (WP_I and WP_I+R) were highest with the 20 kPa irrigation threshold, and WP_I of DSR-20 kPa was 30–50% higher than of PTR-20 kPa. There was a consistent trend for declining ET with decreasing frequency of irrigation, but there was no effect of establishment method on ET apart from higher ET in DSR than PTR with daily irrigation. Water productivity with respect to ET (WP_ET) was highest with a 20 kPa irrigation threshold, with similar values for DSR and PTR. An irrigation threshold of 20 kPa was the optimum in terms of maximising grain yield, WP_I and WP_I+R for both PTR and DSR. Dry seeded rice with the 20 kPa threshold outperformed PTR-20 kPa in terms of WP_I through maintaining yield while reducing irrigation input by 30–50%.