Genotype by environment interactions in barley (<Emphasis Type="Italic">Hordeum</Emphasis><Emphasis Type="Italic"> vulgare</Emphasis> L.): different responses of landraces,recombinant inbred lines and varieties to Mediterranean environment

Genotype-by-environment interactions (GEIs) can affect breeding progress because they often complicate the evaluation and selection of superior genotypes. This drawback can be reduced by gaining insights into GEI processes and genotype adaptation. Here, we have studied the GEIs over a set of 24 barley genotypes that were grown across six environments (location-by-year combinations) in Sardinia, Italy. Three groups of genotypes were analysed: barley landraces (LANs), recombinant inbred lines (RILs), and commercial varieties (VARs). The additive main effects and multiplicative interaction (AMMI) model was used for data analysis, and results evidenced no significant differences in grain yield averages for the 24 genotypes. However, there was a relevant GEI for yield mainly between two of the six environments (one characterised by warm pre-anthesis period and high spring rainfalls, and the other characterised by opposite features) and two groups of genotypes (VAR and LAN). Moreover, a negative trade-off between yield levels of genotypes was seen when the barley genotypes were grown in the contrasting environments. Overall, intermediate GEI levels were seen for RILs in comparison to LANs and VARs, and some of the RILs provided valuable yield levels (e.g. RILs 23 and 52). The results thus show the potential usefulness of LANs as a genetic resource for breeding, e.g. to obtain genotypes adapted to Mediterranean environments, such as the RILs analysed in this study. Most of the actual work was carried out when the first author was a PhD student in ‘Agro-meteorology and ecophysiology of agricultural and forest systems’ and she was affiliated to Dipartimento di Scienze Agronomiche e Genetica Vegetale Agraria, Università degli Studi di Sassari, Via E. de Nicola, Sassari 07100, Italy.     

Specific adaptation of barley varieties in different locations in Ethiopia

Barley is one of the most important cereal crops grown for the livelihoods of the poor farmers of Tigray region in northern Ethiopia. As many low input and marginal environments it has benefited less from the yield increases achieved by modern breeding. This has been largely attributed due to genotype × environment intraction (GEI). To investigate the causes of GEI, ten barley varieties including local checks (two farmers developed varieties, four modern varieties and three rare local varieties) were tested over 21 environments. Participatory methods were applied to sample an adequate number of environments spanning the regional diversity. The yielding ability and stability of the varieties was graphically depicted by GGE and PLSR biplot. There were two major groups of environments, the central and northern highlands, the latter with less rainfall and poorer soils. Rainfall per month and total nitrogen level were the environmental variables that differentiated these two groups. In Tigray, rainfall in June and July were negatively correlated with yield, reflecting waterlogging problems. The different varieties were either specifically or widely adapted across the two environments. The variety ‘Himblil’, originating in Tigray, was the highest yielding and also most stable in the region of origin. However, it was inferior to improved varieties (Shege and Dimtu) at high yield levels. The association of earliness with grain yield indicates that the trait can be effectively manipulated within the existing materials. We recommend breeding for drought/water logging resistance based on selection in the target environment as the best strategy to provide stable and high yielding varieties for Tigray.     

Spanish barley landraces outperform modern cultivars at low‐productivity sites

Barley landraces from the western Mediterranean area have not been thoroughly exploited by modern breeding. This study aims at assessing the agronomic value of a core collection of lines derived from landraces of Spanish origin and to compare them with sets of successful old and modern cultivars. The agronomic performance of a set of 175 barley genotypes, comprising 159 landrace‐derived lines and 26 cultivars, was evaluated in a series of 10 field trials, carried out over 3 years and several locations. The most relevant trait of the landraces was higher grain yield at low production sites than cultivars, which may be related with better ability to fill the grain under stressful conditions. On the other hand, lateness, excessive plant height and lodging were negative traits frequently found in the landraces. Large genotype‐by‐environment interaction (GEI) for grain yield was detected, related partly with differences between germplasm groups, probably indicating local adaptation. GEI was also associated with the interaction of heading time and powdery mildew resistance with temperature.     

Studying the effect of environmental variables on the genotype × environment interaction of tomato

Genotype × environment interaction (GEI) affects marketable fruit yield and average fruit weight of both hybrid and open-pollinated (OP) tomato genotypes. Cultivars vary significantly for marketable fruit yield, with hybrid cultivars having, on average, higher yield than OP cultivars. However, information is scanty on environmental factors affecting the differential response of tomato genotypes across environments. Hence, the aim of this research was to use factorial regression (FR) and partial least squares (PLS) regression, which incorporate external environmental and genotypic covariables directly into the model for interpreting GEI. In this research, data from an FAO multi-environment trial comprising 15 tomato genotypes (7 hybrid and 8 OP) evaluated in 18 locations of Latin America and the Caribbean were analyzed using FR and PLS. Environmental factors such as days to harvest, soil pH, mean temperature (MET), potassium available in the soil, and phosphorus fertilizer accounted for a sizeable portion of GEI for marketable fruit yield, whereas trimming, irrigation, soil organic matter, and nitrogen and phosphorus fertilizers were important environmental covariables for explaining GEI of average fruit weight. Locations with relatively high minimum and mean temperatures favored the marketable fruit yield of OP heat-tolerant lines CL 5915-223 and CL 5915-93. An OP cultivar (Catalina) and a hybrid (Apla) showed average marketable fruit yield across environments, while two hybrids (Sunny and Luxor) exhibited outstanding marketable fruit yield in high yielding locations (due to lower temperatures and higher pH) but a sharp yield loss in poor environments. Two stable hybrid genotypes in high yielding environments, Narita and BHN-39, also showed high and stable yield in average and low yielding environments.     

Recurrent selection for broad adaptation affects stability of oat

A recurrent selection program for adaptation to diverse environments was successful in improving mean oat (Avena sativa L.) grain yield within and across testing environments. The objectives of this research were to determine if this selection program also resulted in changes in other agronomic traits or altered yield stability. Additionally, we investigated how selection modified the response of genotypes to climatic conditions. We evaluated random samples of 100 families from the original population and each of three selection cycle populations in replicated yield trials in Idaho, Iowa, and Norway for two years. Yield stability was assessed via joint regression analysis and superiority analysis. For each cycle, genetic relationships among yields observed indifferent environments were assessed by estimating phenotypic correlations between pairs of target environments. The effect of climate variables on genotype-by-environment interaction (GEI) responses was determined with partial least squares regression. Selection resulted in a small increase in mean heading date, a decrease in mean test weight, and no change in total above-ground biomass or plant height. Genotypic regression coefficients on environmental indices and deviations from regression were larger in the last cycle population, but superiority analysis demonstrated that selection significantly improved the adaptability of the population to the target testing environments. Improved adaptation was also demonstrated by increased phenotypic correlations among the most divergent pairs of environments in the later cycles. Partial least squares regression of GEI effects on climate variables suggested that later cycle families tended to respond more favorably to cooler than average conditions than the original population. Selection resulted in improved yield stability as well as improved mean yield. This revised version was published online in August 2006 with corrections to the Cover Date.     

Relationship between barley grain yield measured in low- and high-yielding environments

Summary The paper addresses the general question of identifying the optimum environment for selection in plant breeding programs for low input agricultural systems. After defining low-yielding and high-yielding environments based on the average grain yield of large numbers of barley genotypes in different cropping seasons, we examined: 1) the phenotypic relationships between the highest yielding genotypes in low- and high-yielding environments, and 2) the genetic correlation coefficients between grain yield in low- and high-yielding environments. The results indicate that the alleles controlling high grain yield in low-yielding conditions are at least partially different from those controlling high grain yield in high-yielding conditions. Therefore, selection in high-yielding environments is expected to produce a negative response or no response in low-yielding environments. This may explain why crop varieties bred under high-yielding conditions failed to have an impact in low-yielding agricultural systems. The results may be extrapolated to systems where environmental concern suggests a reduction of inputs by raising the question of whether crop breeding programs based on selection under high inputs are likely to generate the right type of germplasm for an environmentally friendly agriculture.     

Genetic effects of Vrn genes on heading date and agronomic traits in bread wheat

Summary The Vrn1, Vrn2 and Vrn3 genes have different values of effects on heading date and related yield components. The genetic background and environment do not affect the ranking of Vrn genotypes according to earliness within near-isogenic line sets; however, they do influence the level of differences between heading dates of particular genotypes and between effect values, respectively. The frequencies of defined Vrn genotypes in the global set of spring bread wheat cultivars are associated with grain weight per plant predicted on the basis of Vrn gene effects averaged over backgrounds and over environments. Peculiarities of backgrounds and environments alter the grain yield ranges of Vrn genotypes. For early photoperiod-insensitive wheats, planted in stress conditions at grain filling, the highest yield was predicted for double dominant Vrn genotypes with Vrn3. This gene is rarely used by the breeders in middle latitudes and its wider adoption is encouraged.     

Performance of spring barley (Hordeum vulgare) varieties under organic and conventional conditions

Organic agriculture needs spring barley varieties that are adapted to organic growing conditions and have good and stable grain yield across years, even under less favourable growing conditions. The aim of this study was to compare how varieties differ in yield and yield stability under conventional and organic management conditions. The results help to decide under which growing conditions selection of genotypes for organic farming can be most effective. Grain yield and yield components of 10 varieties were estimated in field trials for three years at four sites: two conventionally and two organically managed sites. Varieties differed in stability: some varieties had high yield under conventional conditions and relatively high and stable yield under organic conditions. Heritabilities for yield and yield components were lower under organic (especially in the field with low weed control) than under conventional conditions. Heritabilities for yield components were lower than those for yield itself. Selection for yield components, therefore, may be less effective than selection directly for grain yield. Our data showed that generally the top performing cultivars under conventional conditions also performed as the best under organic conditions, but there were also exceptions. Therefore we conclude that selection of genotypes for organic farming may take place under conventional conditions, but that a final testing should be conducted under organic conditions to confirm the suitability of the selected varieties for cultivation on organic farms.     

Changes over time in the adaptation of barley releases in north-eastern Spain

The objective of this study was to characterize grain yield and adaptation of barley cultivars released in recent decades in north-eastern Spain. Ten six-rowed and 10 two-rowed barley genotypes were grown in eight environments. Mean yields varied among environments between 1.7 and 5.8 tha^?1. New releases showed higher mean yields and were specifically adapted to nonlimiting growing conditions. The average genetic advances were estimated as 40.7 and 32.9 kg ha^?1 years^?1 for two- and six-rowed genotypes, respectively, in the four most productive environments. Old genotypes, with lower overall grain yields, were specifically adapted to the poorer sites. A negative genetic gain, estimated as -14.8kg ha^?1 years^?1. was reorded for six-rowed culiivars in the four poorest sites. No significant association was observed between heading date and year of release. Variations in carbon isotope discrimination (Δ) were examined to assess whether changes in adaptation could be partially explained by shifts in the genoiypic transpiration efficiency (TE) over time, in the most favourable environments, new releases showed the highest grain yields and carbon isotope discrimination values (Δ). By contrast, older cultivars had constitutively? lower Δs and therefore higher TEs. These results suggest a genetic association between low TE and yield potential and specific adaptation to stress-free conditions so that selection for yield under favourable conditions could have resulted in an indirect downward genetic shift in the TE of modern cultivars.     

Adaptability and stability analysis of groundnut genotypes using AMMI model and GGE-biplot

Unpredictable rainfall, variations in farm inputs, crop-diseases, and the inherent potential of genotypes are among the major factors for low and variable crop yield. Fourteen elite groundnut genotypes were examined in 14 environments to analyze adaptability and stability of genotypes, and identify mega-environments if they exist. Additive main effect and multiplicative interaction (AMMI) model, cultivar-superiority measure, and genotype plus genotype-by-environment (GGE) biplot analysis were used for data analysis. The environment (69.8%) and genotype-by-environment interaction (GEI) effects (21.4%) were dominating the genotypic effect (8.8%). The GEI was significant (P < 0.01), and two distinct environments (mega-environments) were identified, suggesting separate national groundnut breeding strategies for Babile and Pawe. ICGV-94100 and ICGV-97156 were stable and had the highest-yield at Babile and Pawe, respectively. The higher heritability value was recorded in more homogeneous and favorable environments, indicating the genetic potential of groundnut genotypes were better attained in more homogeneous and favorable environments. AMMI model, cultivar-superiority measure, and GGE biplots were helpful methodologies and complemented each other to evaluate the adaptability and stability of groundnut genotypes in diverse environments.     

Quantitative genetic studies on breeding maize for adaptation to organic farming

Organic farming has gained in importance in Germany during recent years. Therefore an increasing demand exists for varieties with specific adaptation to this farming system. In the present study we therefore conducted comparative field experiments with modern maize breeding materials under organic versus conventional farming conditions (ORG and CON, respectively) to estimate quantitative genetic parameters needed for developing optimal breeding strategies and to investigate the perspectives of selection for specific adaptation to ORG. Starting from two broad samples of elite germplasm, consisting of 178 flint and dent lines, respectively, fractions of 11 flint and 11 dent lines were selected based on their testcross performance under ORG. A corresponding set of lines was selected under CON. Testcross performance was evaluated in three regions of Germany and selection of superior lines was practiced across two stages in 2004 and 2005, respectively. The specifically selected lines were crossed in a factorial manner for production of experimental inter-pool single-cross hybrids which were field-tested under ORG and CON in two regions in 2006. Average grain yields were about 16% lower under ORG than under CON. Variance components and entry-mean heritability coefficients under ORG largely resembled those obtained under CON. Phenotypic correlations between ORG and CON were moderate for grain yield and strong for grain dry matter content. No consistent estimates were obtained for the corresponding genotypic correlation for grain yield. At the first stage of testcross selection no evidence of specific adaptation to ORG or CON was observed whereas the factorial crosses tested in 2006 displayed distinct, yet non-significant, advantages when evaluated under the respective target farming system. A small top fraction of hybrids showed outstanding performance under both ORG and CON. The chances of detecting such broadly adapted genotypes are increased if ORG test sites are included in the regular testing system.     

Selection environment and environmental sensitivity in barley

Summary Groups of 10 barley genotypes were selected for high grain yield under either high yielding (two groups) or low yielding conditions (two groups). The genotypes had a similar average grain yield across a wide range of yielding conditions, but differed in their linear response over environments (environmental sensitivity). The genotypes selected for high grain yield under low yielding conditions were less sensitive to changing environments than genotypes selected for high grain yield under high yielding conditions. The higher stability of genotypes selected under low yielding conditions was shown by both the linear regression analysis and the comparison of coefficients of variation. The use of a safety-first index showed that the probability of a crop failure of genotypes selected for high grain yield under high yielding conditions was between 1.8 and 2.7 times higher than for genotypes selected for high grain yield under low yielding conditions. The development of new cultivars for areas where a large proportion of the crop is grown by subsistence farmers should therefore be based on selection under low yielding conditions.     

Genotype-by-environment effects on the performance of recombinant inbred lines of Virginia-type peanut

Peanut (Arachis hypogaea L.) is known to be sensitive to genotype-by-environment interaction (GEI) effects. While previous studies have reported strong GEI effects on peanut yield, most of those studies involved a relatively small number of unrelated genotypes. We examined the extent of GEI effects in elite Virginia-type peanut using a large population of recombinant inbreed lines (RILs). Two-hundred-sixty-six F₇ RILs derived from different cultivars were grown in three environments. Net pod yield (NPY) was evaluated along with 11 other traits. ANOVA revealed that genotype and environment affected all of the examined traits, except for the triplet trait. The substantial influence of the environment was also demonstrated in a genetic-parameter analysis, in which the phenotypic variation coefficients were almost double those for genotypic variation. Still, relatively high heritability and genetic gain values were found for pod weight and NPY. Since NPY is the main target for selection, it was analyzed further. Path analysis showed that NPY is most directly influenced by pod weight and the shelling ratio. A significant GEI effect on NPY was identified using an AMMI model that described 42.7% of the total variation. This GEI component was subjected to a principal components analysis, which confirmed that the variability due to the different environments was greater than the variability that could be attributed to the different genotypes. Yet, several lines had stable yields across environments. These results demonstrate the importance of multi-location phenotyping for QTL analyses and crop improvement in peanut.     

Relationships among economic characters in lentil

Summary There are several reports of the association among lentil characters based on a few, relatively similar lines grown in single environments. Their results have often been inconsistent because of inadequate sampling of genotypes and environments. This study examined associations between economic characters in lentil over a wide range of genetic material and environments in West Asia. The first part of the study concerned correlations within large samples from the world lentil collection grown in two seasons, and the second part covered a smaller sample of genetic material from the collection sown over a wider range of conditions.The results showed similar phenotypic correlations over two seasons, contrasting in rainfall, in the world lentil collection. Similar genetic and phenotypic correlations were also shown by the smaller sample of germplasm over 10 environments. These results indicated low importance of covariance due to environmental and genotype-environment interaction effects. Seed yield was positively correlated with straw yield, indicating selection for either character will increase the other trait. The correlation between seed protein content and seed yield was small and negative, while the correlation of protein with straw yield was positive in sign. This suggests that the current ICARDA goals of selection for high seed and straw yield will not have a major correlated effect on seed protein content. There was a strong positive correlation between seed size and cooking time (r=0.96), therefore seed size can be used to predict cooking time.     

The relation between grain yield and some related traits of spring barley (Hordeum vulgare L.) and their usefulness in a breeding program

Summary The objective of this study was to evaluate traits which can facilitate and improve selection for grain yield of spring barley. Five experiments were conducted in different environments to measure grain yield and yield related traits of breeding lines and exotic varieties. Differences for rate of canopy expansion were significant and offer the opportunity to select for a high weed suppressing potential but there was no relation to grain yield. Dry matter yield/m² at anthesis and its water-soluble-carbohydrate content were not correlated with grain yield/m² and number of grains/m². Variation in biomass among breeding lines with a similar development and plant height was small. Biomass standardized for plant height was stable across environments and showed a good correlation with number of grains and grain yield. The contribution of pre-anthesis assimilation to grain yield was only important under low yielding experimental conditions, but the differences among the genotypes for this trait were inconsistent. It may be difficult to select genotypes with a high potential contribution of pre-anthesis assimilation to grain yield.     

Functional mechanisms of drought tolerance in maize through phenotyping and genotyping under well watered and water stressed conditions

Developing tolerant genotypes is crucial for stabilizing maize productivity under drought stress conditions as it is one of the most important abiotic stresses affecting crop yields. Twenty seven genotypes of maize (Zea mays L.) were evaluated for drought tolerance for three seasons under well watered and water stressed conditions to identify interactions amongst various tolerance traits and grain yield as well as their association with SSR markers. The study revealed considerable genetic diversity and significant variations for genotypes, environment and genotype × environment interactions for all the traits. The ranking of genotypes based on drought susceptibility index for morpho-physiological traits was similar to that based on grain yield and principal component analysis. Analysis of trait – trait and trait – yield associations indicated significant positive correlations amongst the water relations traits of relative water content (RWC), leaf water potential and osmotic potential as well as of RWC with grain yield under water stressed condition. Molecular analysis using 40 SSRs revealed 32 as polymorphic and 62 unique alleles were detected across 27 genotypes. Cluster analysis resulted in categorization of the genotypes into five distinct groups which was similar to that using principal component analysis. Based on overall performance across seasons tolerant and susceptible genotypes were identified for eventual utilization in breeding programs as well as for QTL identification. The marker-trait association analysis revealed significant associations between few SSR markers with water relations as well as yield contributing traits under water stressed conditions. These associations highlight the importance of functional mechanisms of intrinsic tolerance and cumulative traits for drought tolerance in maize.     

Are specific testing protocols required for organic onion varieties? Analysis of onion variety testing under conventional and organic growing conditions

Organic growers need information on variety performance under their growing conditions. A 4-year onion variety research project was carried out to investigate whether setting up a variety testing system combining conventional and organic variety trials is feasible and efficient rather than organizing separate variety trials under the two management systems. During 4 years commercial onion cultivars were tested at a certified organic and a non-organic location. Both systems were managed without chemical pest, disease and sprouting control, but differed in fertility management (organic manure in autumn versus synthetic fertilizer), soil cultivation and weed management (mechanical weeding versus application of herbicide). Management system significantly affected plant density, thickness of neck, and proportion of small and large bulbs. Variety × management system interactions were significant for bulb uniformity, earliness, proportion of large bulbs, dormancy and relative storage success but did not change the ranking of the varieties. We conclude that organic growers can profit from a more conscious variety choice when conventionally fertilised trials would refrain from using pesticides, fungicides, herbicides and sprout inhibitors. However, this would require an adaptation of the management protocol in such a way that trials might no longer represent conditions of conventional farmers. Furthermore, assessments of leaf erectness, disease resistance to downy mildew and leaf blight should be included in the protocols for organic use. We advocate better communication between breeders and growers on specific variety characteristics contributing to improving yield stability under low-input, organic growing conditions.     

Agronomic performance of winter wheat grown under highly divergent soil moisture conditions in rainfed and water‐managed environments

Even in the temperate climates of Europe, increasing early season drought and rising air temperature are presenting new challenges to farmers and wheat breeders. Sixteen winter wheat (Triticum aestivum L.) genotypes consisting of three hybrids, six line cultivars and two breeding lines from Germany as well as five line cultivars from France, Austria, Slovakia, Hungary and the Ukraine (referred to as “exotic” lines) have been included in this study. The genetic materials were evaluated over three growing seasons under a range of soil moisture regimes at the three North German sites Braunschweig (irrigated and drought‐stressed), Warmse (rainfed) and Söllingen (rainfed). The average grain yields in the twelve growth environments (water regime × season combinations) ranged from 6.1 to 13.5 t ha^?1. The exotic lines showed little evidence of specific phenological adaptation to drought although they are frequently faced with water scarcity in their countries of origin. The hybrids and German lines exhibited higher regression coefficients (b_i) to environmental means than the exotic lines, indicating particular adaptation to favourable growing conditions. The phenotypical correlations of grain yield between the various environments were high, ranging for instance from 0.6 to 0.8 for the irrigated and drought‐stressed environments at Braunschweig. It is thus expected that in the foreseeable future continued selection aiming at high yield potential will suffice as a means to counter the expected increase in droughts.     

Specific adaptation and breeding for marginal conditions

Summary Breeding has been very successful in generating cultivars that in favorable environments, and together with large use of fertilizer and chemical control of weeds, pest and diseases, have increased agricultural production several fold. Today the environmental impact of high input agriculture in more favorable environments causes growing concern. By contrast, the impact of breeding in marginal environments has been elusive. The paper discusses evidence showing that the use of breeding principles developed for, and successfully applied, in favorable environments may be the main reason for the lack of breeding progress in marginal environments. Very little breeding work has actually been done in marginal environments, although the theory of correlated responses to selection indicates that selection conducted in good environments or in well-managed experiment stations is not expected to be very efficient when genotype by environment interactions of a cross-over type exist. The assumptions that heritability is higher under good conditions and that there is a carry-over effect of high yield potential are not supported by experimental evidence. If the target environment is below the cross-over point, selection has to be conducted for specific adaptation to that environment. The concept of wide adaptation has more a geographical than an environmental meaning, and it reduces genetic diversity and increases genetic vulnerability. Eventually the issue of genetic heterogeneity versus genetic uniformity is discussed in relation to specific adaptation to marginal environments.     

Performance stability of maize genotypes across diverse hill environments in Nepal

The national maize improvement program in Nepal regularly receives elite maize (Zea mays L.) genotypes from CIMMYT and other countries and tests them for their performance stability in highly diverse environments. Studies were conducted on research stations and farmers’ fields at five sites in three years to determine performance stability of exotic maize genotypes. Replicated on-station and on-farm studies were conducted using 25 and 10 genotypes, respectively, including a local check and an improved check (Manakamana-3), in 2004–2006. We analyzed grain yield, days to flowering, plant and ear height, plant population, husk cover, and plant and ear aspect. Stability and genotype superiority for grain yield was determined using genotype and genotype × environment (GGE) biplot analysis that compares among a set of genotypes with a reference ‘ideal’ genotype, which has the highest average value of all genotypes and is absolutely stable. Several genotypes produced significantly higher grain yield than the local check. Four genotypes (‘Across9942 × Across9944’, ‘Open Ended White Hill Population’, ‘Population 44C10’ and ‘ZM621’), that produced significantly higher grain yield than the improved check, also had other agronomic traits (days to flowering, plant and ear height, number of ears, resistance to leaf blight, plant and ear aspect and husk cover tightness) equal to or better than the improved check. GGE-biplot analysis showed that Across9942 × Across9944 and ZM621 were the most superior genotypes in the on-station and on-farm trials, respectively. The findings from this study provide new information on the stability of the maize genotypes that are also adapted to other regions of the world. Such information could be useful for maize improvement program for the highlands in Nepal and other similar environments.