Well-watered Environments Research Articles

Variation in drought-tolerance components and their interrelationships in the core collection of foxtail millet (Setaria italica) germplasm

Foxtail millet (Setaria italica (L.) P.Beauv.) is an ancient cereal cultivated worldwide in arid and marginal lands. It is an ideal crop for the changing climate, with high photosynthetic efficiency. A trait-based selection for drought tolerance is sought for yield stability. The present work had segregated the drought yield as total water use (T), transpiration efficiency (TE) and harvest index (HI) and assessed the importance of these components and their association with drought tolerance. The core collection of foxtail millet germplasm (n = 155) was evaluated in mini-lysimeters under both terminal drought stress (DS) and well-watered (WW) environments. The contribution of T to grain yield under drought was minor but the contribution of TE was positive and of HI negative. Crop duration, T and TE positively influenced, and HI negatively influenced, shoot biomass production. Under drought, the core germplasm accessions varied in shoot biomass, grain yield, HI and T by >3-fold and in TE by 2-fold. Categorisation of the germplasm for TE had differentiated groups of accessions as high TE (n = 17) and low TE (n = 22). Among the three races of foxtail millet, indica was strong for T and TE, and maxima and moharia for HI, with useful exceptions.

Genome-wide identification and characterization of aquaporin gene family in common bean (Phaseolus vulgaris L.).

Plant aquaporins are a large and diverse family of water channel proteins that are essential for several physiological processes in living organisms. Numerous studies have linked plant aquaporins with a plethora of processes, such as nutrient acquisition, CO2 transport, plant growth and development, and response to abiotic stresses. However, little is known about this protein family in common bean. Here, we present a genome-wide identification of the aquaporin gene family in common bean (Phaseolus vulgaris L.), a legume crop essential for human nutrition. We identified 41 full-length coding aquaporin sequences in the common bean genome, divided by phylogenetic analysis into five sub-families (PIPs, TIPs, NIPs, SIPs and XIPs). Residues determining substrate specificity of aquaporins (i.e., NPA motifs and ar/R selectivity filter) seem conserved between common bean and other plant species, allowing inference of substrate specificity for these proteins. Thanks to the availability of RNA-sequencing datasets, expression levels in different organs and in leaves of wild and domesticated bean accessions were evaluated. Three aquaporins (PvTIP1;1, PvPIP2;4 and PvPIP1;2) have the overall highest mean expressions, with PvTIP1;1 having the highest expression among all aquaporins. We performed an EST database mining to identify drought-responsive aquaporins in common bean. This analysis showed a significant increase in expression for PvTIP1;1 in drought stress conditions compared to well-watered environments. The pivotal role suggested for PvTIP1;1 in regulating water homeostasis and drought stress response in the common bean should be verified by further field experimentation under drought stress.

Genomic prediction in biparental tropical maize populations in water-stressed and well-watered environments using low-density and GBS SNPs.

One of the most important applications of genomic selection in maize breeding is to predict and identify the best untested lines from biparental populations, when the training and validation sets are derived from the same cross. Nineteen tropical maize biparental populations evaluated in multienvironment trials were used in this study to assess prediction accuracy of different quantitative traits using low-density (~200 markers) and genotyping-by-sequencing (GBS) single-nucleotide polymorphisms (SNPs), respectively. An extension of the Genomic Best Linear Unbiased Predictor that incorporates genotype × environment (GE) interaction was used to predict genotypic values; cross-validation methods were applied to quantify prediction accuracy. Our results showed that: (1) low-density SNPs (~200 markers) were largely sufficient to get good prediction in biparental maize populations for simple traits with moderate-to-high heritability, but GBS outperformed low-density SNPs for complex traits and simple traits evaluated under stress conditions with low-to-moderate heritability; (2) heritability and genetic architecture of target traits affected prediction performance, prediction accuracy of complex traits (grain yield) were consistently lower than those of simple traits (anthesis date and plant height) and prediction accuracy under stress conditions was consistently lower and more variable than under well-watered conditions for all the target traits because of their poor heritability under stress conditions; and (3) the prediction accuracy of GE models was found to be superior to that of non-GE models for complex traits and marginal for simple traits.

International Research Journal of Agricultural Science and Soil Science

Haploid breeding via in vivo induction of maternal haploids is rapidly replacing the pedigree breeding methods since it reduces the breeding cycle from at least 6 to 1-2 generations to reach a homozygous state. Eighty doubled haploid (DH) lines derived from nine tropical maize backcross populations were crossed to two CIMMYT single cross testers (CML312/CML442 and CML395/CML444) in a North Carolina II mating design. The resultant 160 DH testcross hybrids and five commercial checks were evaluated across four well-watered locations and two drought stressed locations in Kenya using an alpha-lattice design of 15 x 11 replicated twice. Significant differences (0.05 < p < 0.001) were observed in location, genotype and genotype by environment interaction for grain yield, days to anthesis, anthesis-silking interval and ear aspect under nonstress conditions. Combined analyses across drought stress and well-watered environments showed that the top 20 hybrids performed better for grain yield and other agronomic traits of maize compared to the commercial checks. Grain yield for the top 20 DH hybrids ranged from 8.15-8.85 t/ha under optimum management and 4.53-5.67 t/ha under drought stress conditions while the best commercial variety yielded 7.67 t/ha and 3.43 t/ha under optimum and drought stress conditions, respectively. The top ten DH testcross hybrids averaged over the four optimum locations yielded 16% higher than the best commercial check while under managed drought the top ten DH hybrids produced 62% higher grain yield than the best commercial check. Three DH testcross hybrids entries 23, 28 and 71 performed highly for grain yield under both stress and non-stress locations high stress tolerance indices (STI) and low stress susceptibility indices (SSI). These results indicated that maize hybrids developed from DH lines produced as high a grain yield and as acceptable agronomic traits as the commercial hybrids developed through conventional pedigree methods. The DH lines identified in the study should be useful in improving grain yields and in the drought prone mid-altitude areas of eastern and southern Africa.

Winter Wheat Quality Responses to Water, Environment, and Nitrogen Fertilization

Decreasing carbon (C) footprints by reducing nitrogen (N) and water inputs has been speculated to have negative impacts on wheat grain yield and flour processing quality. The objective of this study was to determine the impact of N and water stress on winter wheat grain yield, protein composition, and dough quality. Wheat fertilized at two N rates (unfertilized and recommended) was grown under water-stressed and well-watered environments. Nitrogen and water stress were measured using the 13C isotopic approach. Research showed that (1) N fertilizer and the water-management environment produced similar impacts on wheat quality and yield loss due to N stress and yield loss due to water stress (YLWS); (2) N fertilizer increased flour protein, dough stability, and relative concentration of glutenin (%Glu), unextractable polymeric protein (UPP), and relative amount of high-molecular-weight glutenin subunits (HMW-GS/LMW-GS); (3) the well-watered environment reduced protein contents when N mineralization was low, whereas it did not influence protein content when mineralization was high; and (4) the %Glu was negatively correlated with yield loss due to N stress (YLNS) and positively correlated with stability. This study showed that a clear understanding of the complex relationship between soil variability and climatic conditions should make it possible to develop adaptive management practices, increase profitability, and improve quality.

Vernalization gene combination to maximize grain yield in bread wheat (Triticum aestivum L.) in diverse environments

The major vernalisation genes of VRN1 are well understood at the molecular level. However, their quantitative contributions to flowering time and grain yield related traits are not clear. In this study, we used a double haploid population (225 lines) of Westonia × Kauz in which the Vrn-A1a (Westonia), Vrn-B1a (Westonia) and Vrn-D1a (Kauz) were segregating, and a high resolution genetic map of 1,159 loci, to determine the quantitative contributions of Vrn-A1a, Vrn-B1a and Vrn-D1a for the days to anthesis and grain yield related traits in diverse environments. The major quantitative trait loci (QTL) of spikelet number per spike and days to anthesis were contributed by the winter alleles of VRN1. The QTL of the time of grain filling were contributed by the spring alleles of VRN1. The wild genotype (vrn-A1vrn-B1vrn-D1) showed the latest flowering, the highest spikelet number per spike, lowest peduncle proportion and thousand grain weight in three environmental analyses, and the largest spikelet number per spike, which resulted in high kernel number per spike (KN) and grain weight (GW) in well-watered environments. One QTL of KN was located on 5B, contributed by winter allele of vrn-B1 in three environmental analyses, and one GW QTL was detected on 5A, contributed by the spring allele of Vrn-A1a in a drought environment. The results indicated that the genotype Vrn-A1avrn-B1Vrn-D1a would shorten the time to anthesis and give high GW and KN in drought environments. The early anthesis associated phenotype, peduncle proportion would provide an indicator in breeding programs.

Genetic distance among doubled haploid maize lines and their testcross performance under drought stress and non-stress conditions

In contrast to conventional inbreeding that takes up to seven generations to develop inbred lines, the doubled haploid (DH) technology allows production of inbred lines in two generations. The objectives of the present study were to: (a) evaluate testcross performance of 45 doubled haploid lines under drought stress and non-stress conditions (b) estimate heritabilities for grain yield and other traits and (c) to assess the genetic distance and relationship among the DH lines using 163,080 SNPs generated using genotyping-by-sequencing (GBS). The 45 hybrid and five checks were evaluated using a 10 × 5 alpha lattice in six drought stress and nine well-watered environments in Kenya, Uganda, and Tanzania. Differences in trait means between the drought stress and well-watered conditions were significant for all measured traits except for anthesis date. Genetic variances for grain yield, grain moisture, plant height and ear height were high under well-watered environments while genetic variance for anthesis date, root lodging and stalk lodging were high under drought stress environments. Combined analyses across drought stress and well-watered environments showed that ten top hybrids produced 1.6–2.2 t/ha grain yield under well-watered condition and 1–1.4 t/ha under drought stress condition higher than the mean of the commercial checks. Genetic distance between pairwise comparisons of the 38 of the 45 DH lines ranged from 0.07 to 0.48, and the overall average distance was 0.36. Both cluster and principal coordinate analysis using the genetic distance matrix calculated from 163,080 SNPs showed two major groups and the patterns of group was in agreement with their pedigree. Thirteen (13) of the best hybrids are currently in National Performance Trials testing, an important step towards commercialization in Kenya, Tanzania and Uganda.

Meta-analyses of QTL for grain yield and anthesis silking interval in 18 maize populations evaluated under water-stressed and well-watered environments

BackgroundIdentification of QTL with large phenotypic effects conserved across genetic backgrounds and environments is one of the prerequisites for crop improvement using marker assisted selection (MAS). The objectives of this study were to identify meta-QTL (mQTL) for grain yield (GY) and anthesis silking interval (ASI) across 18 bi-parental maize populations evaluated in the same conditions across 2-4 managed water stressed and 3-4 well watered environments.ResultsThe meta-analyses identified 68 mQTL (9 QTL specific to ASI, 15 specific to GY, and 44 for both GY and ASI). Mean phenotypic variance explained by each mQTL varied from 1.2 to 13.1% and the overall average was 6.5%. Few QTL were detected under both environmental treatments and/or multiple (>4 populations) genetic backgrounds. The number and 95% genetic and physical confidence intervals of the mQTL were highly reduced compared to the QTL identified in the original studies. Each physical interval of the mQTL consisted of 5 to 926 candidate genes.ConclusionsMeta-analyses reduced the number of QTL by 68% and narrowed the confidence intervals up to 12-fold. At least the 4 mQTL (mQTL2.2, mQTL6.1, mQTL7.5 and mQTL9.2) associated with GY under both water-stressed and well-watered environments and detected up to 6 populations may be considered for fine mapping and validation to confirm effects in different genetic backgrounds and pyramid them into new drought resistant breeding lines. This is the first extensive report on meta-analysis of data from over 3100 individuals genotyped using the same SNP platform and evaluated in the same conditions across a wide range of managed water-stressed and well-watered environments.

QTL mapping in three tropical maize populations reveals a set of constitutive and adaptive genomic regions for drought tolerance

Despite numerous published reports of quantitative trait loci (QTL) for drought-related traits, practical applications of such QTL in maize improvement are scarce. Identifying QTL of sizeable effects that express more or less uniformly in diverse genetic backgrounds across contrasting water regimes could significantly complement conventional breeding efforts to improve drought tolerance. We evaluated three tropical bi-parental populations under water-stress (WS) and well-watered (WW) regimes in Mexico, Kenya and Zimbabwe to identify genomic regions responsible for grain yield (GY) and anthesis-silking interval (ASI) across multiple environments and diverse genetic backgrounds. Across the three populations, on average, drought stress reduced GY by more than 50 % and increased ASI by 3.2 days. We identified a total of 83 and 62 QTL through individual environment analyses for GY and ASI, respectively. In each population, most QTL consistently showed up in each water regime. Across the three populations, the phenotypic variance explained by various individual QTL ranged from 2.6 to 17.8 % for GY and 1.7 to 17.8 % for ASI under WS environments and from 5 to 19.5 % for GY under WW environments. Meta-QTL (mQTL) analysis across the three populations and multiple environments identified seven genomic regions for GY and one for ASI, of which six mQTL on chr.1, 4, 5 and 10 for GY were constitutively expressed across WS and WW environments. One mQTL on chr.7 for GY and one on chr.3 for ASI were found to be ‘adaptive’ to WS conditions. High throughput assays were developed for SNPs that delimit the physical intervals of these mQTL. At most of the QTL, almost equal number of favorable alleles was donated by either of the parents within each cross, thereby demonstrating the potential of drought tolerant × drought tolerant crosses to identify QTL under contrasting water regimes.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-012-2003-7) contains supplementary material, which is available to authorized users.

Evaluation of the reaction of durum wheat genotypes (Triticum durum Desf.) to drought conditions using various stress tolerance indices

In this study, 40 genotypes of durum wheat (Triticum durum) originating from Iran and Azerbaijan Republic were evaluated in both water-stressed and well-watered environments in 3 years 2008 to 2011 cropping years. In each environment, the genotypes were evaluated using a randomized complete block design with three replications. From the grain yield data, drought tolerance indices comprising of stability tolerance index (STI), mean productivity (MP), geometric mean productivity (GMP), stress susceptibility index (SSI), tolerance index (TOL), yield index (YI) and yield stability index (YSI) were calculated for every genotype. The resulting data were analyzed as obtained from a randomized complete block design. Significant differences among genotypes were observed for all drought tolerance indices. High yield value in non-stress and stress environments was exhibited by genotypes ‘40 (4411.22 kg ha -1) and ‘32’ (4256.34 kg ha -1) respectively. The maximum value of STI (1.07), MP (3642.11) and GMP (3590.85) indices was by genotype ‘35’. The highest value for YI (1.24) was from genotypes ‘39’ and ‘21’. Correlation coefficients revealed that TOL, MP, GMP, STI, HM, and YI indices could effectively be used for screening of drought tolerant genotypes. Using MP, GMP, TOL, YI and STI indices, genotypes UPGMA classification was done and three clusters were established that is paralleled to biplot analysis results. According to results in this study, G10 and G35 were the most drought tolerant genotypes which were clustered as group A. We suggest that tolerance indices including MP, GMP and STI are suitable for durum wheat drought tolerant genotypes selection. Key words: Biplot, Triticum durum Desf., multivariate analysis, water-stressed condition, yield stability.

High temperature exposure increases plant cooling capacity

Summary Plants inhabit different environments and have evolved mechanisms to optimise growth within defined temperature ranges. In Arabidopsis thaliana , growth at high temperature (28°C) results in striking elongation of stems and increased leaf elevation from the soil surface [1–3]. Despite insights into the molecular control of these responses [1–5], their physiological significance remains unknown. Here, we analysed the impact of high temperature-mediated development on plant water use strategy. We present the surprising finding that Arabidopsis plants developed at high temperature (28°C) show increased water loss and enhanced leaf cooling capacity in these conditions, despite producing fewer leaf surface pores (stomata). Our data suggest that plant architectural adaptations to high temperature may enhance evaporative leaf cooling in well-watered environments.

Hybrid rice performance in environments of increasing drought severity

Hybrid rice provides an option for achieving high yield potential under favorable conditions, but the performance of hybrids under drought stress has not yet been fully evaluated. This study explored the feasibility of using hybrid rice technology in drought-prone rainfed lowland fields. Hybrid lines, parental inbreds, and cultivated varieties as checks were screened for yield potential in well-watered fields and for drought resistance in drained fields at different stress levels. Nineteen out of 45 hybrid lines showed a yield advantage (on average 20%) over check lines in the three well-watered environments. Classifications of drought stress levels were based on the yield reduction relative to the well-watered environments, with moderate, severe, and very severe stress levels resulting in 54%, 77% and 89% reductions in yield, respectively. The relationship between yield advantage of hybrids and drought severity differed among lines; some hybrids showed more of an advantage under severe drought, whereas others had a greater yield advantage under moderate stress. Some hybrids did not perform as well as parents under drought. In general, the harvest index of hybrids was greater than those of inbred parents and checks, and showed strong correlation with grain yield in the different stress environments. Total dry matter yield of hybrids was correlated with improved yield in all stress environments during dry seasons, and some drought-tolerant hybrids also showed greater tillering efficiency and thousand-grain weight. Twenty-four selected hybrid lines were divided into seven clusters on the basis of yield trends across different drought stress environments. Among the hybrid rice lines, one cluster including IR81954H, IR81955H, and IR81956H stood out as combining high yield potential in both well-watered and drought stress environments. Hybrid IR81954H showed an 8% yield advantage over other hybrids across all studies, as well as stable yield in all the stress environments having an average yield advantage of 22% over other hybrids averaged across drought environments. These results highlight the variability among hybrids in their drought response, and the need for screening of hybrids and parents under drought stress conditions.

Large-scale screening for maize drought resistance using multiple selection criteria evaluated under water-stressed and well-watered environments

A total of 550 maize inbred lines collected from global breeding programs were evaluated for drought resistance under both well-watered and water-stressed environments. The evaluation was based on multiple measurements of biomass taken before and after the drought stress was applied using the normalized difference vegetation index (NDVI), along with other selection criteria including anthesis-silking interval, leaf senescence, chlorophyll content, root capacitance, final grain yield, and grain yield components. Kernel weight was the most stable trait under drought stress. Correlations between the primary trait (grain yield) and the secondary traits, except the root capacitance and ASI under water-stressed condition, were all significant. Root capacitance had relatively low heritability and low genetic correlation with other drought resistance criteria, and is not recommended as a drought resistance criterion. Significant reduction of NDVI values measured in the afternoon when the leaves became rolling, compared to those measured in the morning when the leaves were open, provides a reliable index for leaf rolling, which however was not significantly correlated with grain yield. NDVIs measured across different developmental stages were highly correlated with each other and with most of the secondary traits as well as, grain yield, indicating that NDVI can be used as a secondary trait for large-scale drought resistance screening. Regression models built based on non-yield drought criteria and yield components explained about 40% and 95% of the variation for the grain yield, respectively. Some maize lines developed in China for temperate regions showed strong drought resistance comparable to tropical maize lines when tested under tropical condition, indicating that temperate lines with a wide adaptability can be used in drought resistance breeding for both temperate and tropical environments.

Combining ability, heterosis and genetic diversity in tropical maize (Zea mays L.) under stress and non-stress conditions

Drought and low soil fertility are considered the most important abiotic stresses limiting maize production in sub-Saharan Africa. Knowledge of the combining ability and diversity of inbred lines with tolerance to the two stresses and for those used as testers would be beneficial in setting breeding strategies for stress and nonstress environments. We used 15 tropical maize inbred lines to (i) evaluate the combining ability for grain yield (GY), (ii) assess the genetic diversity of this set of inbred lines using RFLP, SSR, and AFLP markers, (iii) estimate heterosis and assess the relationship between F1 hybrid performance, genetic diversity and heterosis, and (iv) assess genotype × environment interaction of inbred lines and their hybrids. The F1 diallel hybrids and parental inbreds were evaluated under drought stress, low N stress, and well-watered conditions at six locations in three countries. General combining ability (GCA) effects were highly significant (P < 0.01) for GY across stresses and well-watered environments. Inbred lines CML258, CML339, CML341, and CML343 had the best GCA effects for GY across environments. Additive genetic effects were more important for GY under drought stress and well-watered conditions but not under low N stress, suggesting different gene action in control of GY. Clustering based on genetic distance (GD) calculated using combined marker data grouped lines according to pedigree. Positive correlation was found between midparent heterosis (MPH) and specific combining ability (SCA), GD and GY. Hybrid breeding program targeting stress environments would benefit from the accumulation of favorable alleles for drought tolerance in both parental lines.

Combining ability of early-maturing quality protein maize inbred lines adapted to Eastern Africa

Adapted early-maturing quality protein maize (QPM) hybrids with high grain yield potential in Eastern Africa would benefit maize farmers through increased grain production and subsequently higher income but they are not widely available. Fourteen early-maturing QPM inbred lines developed from POOL15QPM-SR, were crossed using the diallel mating design. The resulting single-cross hybrids were evaluated under six well-watered, drought stress and low nitrogen conditions at six locations in Eastern Africa. The objectives were to assess the grain yield potential of early-maturing F 1 QPM hybrids, estimate the general combining ability (GCA) and specific combining ability (SCA) for grain yield and other agronomic traits and determine the relationship between grain yield and other agronomic traits of the QPM hybrids. Days to anthesis, days to silking, anthesis–silking interval, ears per plant, root and stalk lodging, ear aspect, and grain yield were measured. Variation among hybrids was significant for all traits except root lodging. The best single-cross hybrid across environments was POOL15QPMFS538-B-3-B-B × POOL15QPMFS462-B-4-B-B (5.30 t ha −1). Mean squares due to GCA were significant, whereas mean squares due to SCA were not for measured traits indicating that additive genetic effects were much more important in this set of genotypes. Inbred line POOL15QPMFS538-B-3-B-B exhibited very good GCA effects for grain yield in well-watered environments and across environments for grain yield (0.74 t ha −1). Inbred line Pool15QPMFS478-B-3-B-B had the best GCA effect for grain yield under managed drought stress (0.26 t ha −1), while inbred line POOL15QPMFS319-B-2-B-B had the best GCA effect (−1.11 days) for reduced days to anthesis across environments. The new QPM inbred lines with desirable traits could be used to improve grain yield and protein quality of maize breeding programs in Eastern Africa.

Quantitative trait loci for carbon isotope discrimination are repeatable across environments and wheat mapping populations

Wheat productivity is commonly limited by a lack of water essential for growth. Carbon isotope discrimination (Delta), through its negative relationship with transpiration efficiency, has been used in selection of higher wheat yields in breeding for rainfed environments. The potential also exists for selection of increased Delta for improved adaptation to irrigated and high rainfall environments. Selection efficiency of Delta would be enhanced with a better understanding of its genetic control. Three wheat mapping populations (Cranbrook/Halberd, Sunco/Tasman and CD87/Katepwa) containing between 161 and 190 F(1)-derived, doubled-haploid progeny were phenotyped for Delta and agronomic traits in 3-5 well-watered environments. The range for Delta was large among progeny (c. 1.2-2.3 per thousand), contributing to moderate-to-high single environment (h (2) = 0.37-0.91) and line-mean (0.63-0.86) heritabilities. Transgressive segregation was large and genetic control complex with between 9 and 13 Delta quantitative trait loci (QTL) identified in each cross. The Delta QTL effects were commonly small, accounting for a modest 1-10% of the total additive genetic variance, while a number of chromosomal regions appeared in two or more populations (e.g. 1BL, 2BS, 3BS, 4AS, 4BS, 5AS, 7AS and 7BS). Some of the Delta genomic regions were associated with variation in heading date (e.g. 2DS, 4AS and 7AL) and/or plant height (e.g. 1BL, 4BS and 4DS) to confound genotypic associations between Delta and grain yield. As a group, high Delta progeny were significantly (P < 0.10-0.01) taller and flowered earlier but produced more biomass and grain yield in favorable environments. After removing the effect of height and heading date, strong genotypic correlations were observed for Delta and both yield and biomass across populations (r (g) = 0.29-0.57, P < 0.05) as might be expected for the favorable experimental conditions. Thus selection for Delta appears beneficial in increasing grain yield and biomass in favorable environments. However, care must be taken to avoid confounding genotypic differences in Delta with stature and development time when selecting for improved biomass and yield especially in environments experiencing terminal droughts. Polygenic control and small size of individual QTL for Delta may reduce the potential for QTL in marker-assisted selection for improved yield of wheat.

Genotype by environment effects and selection for drought tolerance in tropical maize. II. Three-mode pattern analysis

A selection program in three tropical maize populations aimed to improve tolerance of mid-season to late season drought environments while maintaining grain yield (GY) potential. The selection process employed other attributes that included maintaining a constant anthesis date (AD) and, under drought, shortening the anthesis-silking interval (ASI) and increasing ear number per plant (EPP). Three-mode (genotypes x environments x attributes) pattern analysis, which consists of clustering and ordination, should be able to collectively interpret these changes from ten evaluation trials. Mixture maximum likelihood clustering identified four groups that indicated the populations' performance had changed with selection. Groups containing the advanced cycles of selection were higher yielding in most environments and had lower ASI and higher EPP, particularly in drought environments. Check entries with no selection for drought tolerance remained grouped with the initial cycles of selection. A 3 x 2 x 3 (genotypes by environments by attributes) principal component model explained 70% of the variation. For the first environmental component, ASI was shown to be highly negatively correlated with both GY and EPP while anthesis date (AD) was virtually uncorrelated with other traits. The second environmental component (explaining 10% of the variation) contrasted droughted and well-watered environments and showed that EPP and GY were better indicators of this contrast (in terms of changes in population performance) than were AD or ASI. Three-mode analysis demonstrated that improvements with selection occurred in both droughted and well-watered environments and clearly summarised the overall success of the breeding program.

Genotype by environment effects and selection for drought tolerance in tropical maize. I. Two mode pattern analysis of yield

Ten trials evaluated the performance of several late tropical maize populations (La Posta Sequia, Pool 26 Sequia and Tuxpeno Sequia) selected for tolerance to drought during flowering and grain filling and also for yield potential. Families (S1 or full-sib) had been selected recurrently for six to eight years on an index of traits. Pattern (clustering and ordination) analysis was used to analyse the relative performance of entries that included cycles of selection for drought tolerance in the populations and non-drought tolerant checks. Mean environment (E) yields ranged from 1.0 to 10.4 t ha-1. Analysis of variance showed that 97.9% of the total sums of squares was accounted for by E, and that, of the remaining sums of squares the G × E (genotype by environment interaction) was almost 3 times that of the contribution of G alone. Cluster analysis separated the checks, the earlier maturing drought tolerant entries and the later maturing drought tolerant entries. This was verified by principal component (PC) analysis of the G × E matrix. Grouping of the environments (i.e. based on entry performance), resulted in the separation of different types of droughts, and of medium and high yielding well-watered environments. The patterns of discrimination observed indicated that the yield gains under drought would have been unlikely to occur if selection had been done only in well-watered environments. Within each population, selection improved broad adaptation (higher mean yield) to both drought and well-watered environments and cycles of selection ‘jumped’ from non-drought-tolerant to drought-tolerant groups as their specific adaptation to drought environments increased.

Eight cycles of selection for drought tolerance in lowland tropical maize. I. Responses in grain yield, biomass, and radiation utilization

Drought is a major source of grain yield instability in maize ( Zea mays L.) grown in the lowland tropics, and use of cultivars with improved drought tolerance may be the only affordable option for many small-scale farmers. Eight cycles of full-sib recurrent selection were carried out in the population ‘Tuxpeño Sequía’ during the rain-free winter season at Tlaltizapán, Mexico, under controlled moisture stress timed to coincide either with flowering or grain-filling. Selection was based on an index comprising grain yield and physiological and morphological traits with presumed adaptive value under drought. The objectives of this study were to evaluate direct and correlated responses to selection in grain yield and its components, total biomass, and radiation-use efficiency (RUE). Cycles 0, 2, 4, 6 and 8 of Tuxpeño Sequía, and a check cultivar representing the results of six cycles of selection based primarily on multilocation testing, were evaluated under three moisture regimes at Tlaltizapán during two consecutive winter seasons. Grain yield (GY) increased at 108 kg ha −1 cycle −1 across 12 yield environments ranging in yield potential from 1 to 8 Mg ha −1, with no significant interaction between gains and moisture environments. Yield gains resulted from an increase of 0.03 ears per plant (EPP) cycle −1 under drought, and small but significant increases in EPP, kernel number per ear and kernel weight in well-watered environments. Selection had no effect on biomass production, so yield increases were due to a gain in harvest index (HI) of 0.0058 to 0.0067 cycle −1 in either wet or dry environments. Seasonal readiation-use efficiency averaged 1.48 g MJ −1 PAR under well-watered conditions, a value lower than expected for maize. Although selection slightly reduced radiation interception and slightly increased RUE during the pre-anthesis phase, both changes were relatively unimportant. The regression of GY on biomass (B) ( GY = −1.85 + 0.47 B; R 2 = 0.94 ∗∗ ) predicted zero GY at biomass yields of less than 4 Mg ha −1. The check entry showed only limited progress in drought tolerance, EPP, HI, and GY. These results suggest that drought stress, when managed to coincide with flowering, can be an effective selection environment for increasing HI, yield stability, and GY of lowland tropical maize across a wide range of moisture environments.

Evaluation of the reaction of sunflower inbred lines and their F1 hybrids to drought conditions using various stress tolerance indices

In this study, 21 genotypes of sunflower ( Helianthus annuus L.) derived from a half diallel cross between six inbred lines were evaluated in both water-stressed and well-watered environments. In each environment, the genotypes were evaluated using a randomized complete block design with three replications. From the grain yield data, drought tolerance indices comprising of stability tolerance index (STI), mean productivity (MP), geometric mean productivity (GMP), harmonic mean (HM), stress susceptibility index (SSI), tolerance index (TOL), yield index (YI) and yield stability index (YSI) were calculated for every genotype. The resulting data were analyzed as obtained from a randomized complete block design. Significant differences among genotypes were observed for all drought tolerance indices except for SSI and YSI. High yield value in non-stress and stress environments was exhibited by genotypes ‘LR4 × LR25’ (14.02 g) and ‘LR25 × C100’ (3.84 g) respectively. The maximum value of STI (0.93), MP (8.72), GMP (6.91) and HM (5.48) indices was by genotype ‘LR4 × LR25’. Correlation coefficients revealed that TOL, MP, GMP, STI, HM, and YI indices could effectively be used for screening of drought tolerant genotypes. Using MP, GMP, HM, TOL, YI and STI indices, genotypes UPGMA classification was done and three clusters were established that paralleled the biplot analysis results. According to results in this study, ‘LR4 × LR25’ is the most drought tolerant genotype which was clustered as group A. We suggest that tolerance indices including MP, GMP and HM are suitable for sunflower drought tolerant genotypes selection.