CIMMYT Wheat Lines Research Articles

Exploring the variability of root system architecture under drought stress in heat-tolerant spring-wheat lines

Background and aimsGlobal wheat production is under threat due to climate change, specifically heat and drought and their combination. This study aims to address the root trait responses of heat-tolerant wheat genotypes to drought.MethodsThe variability in root traits of CIMMYT wheat lines, which were previously developed for heat stress tolerance (HTWL), was evaluated alongside 10 Pakistani-approved varieties under three cultivation conditions and soil moisture levels.ResultsOur findings revealed that the plasticity of the wheat root system is highly pronounced, with rhizosphere conditions exerting a more substantial influence (5–49%) than the genotypic response (1–14%). Furthermore, in the hydroponic and pot system, we noted higher maximum-root length (1.5–1.8 fold) and root-to-shoot ratio (3.4–10.6 fold) as compared to field condition, while the root biomass was substantially higher in the field trial (3-57 fold). Nonetheless, persistent drought conditions exerted contrasting impact with reduction in most of the traits except specific root length and harvest index which were increased under drought.ConclusionsThe variation in root traits against drought indicates the potential for the development of improved genotypes that can withstand multiple stresses. Furthermore, it is crucial to consider rhizosphere conditions when selecting genotypes, as the plasticity of wheat roots may lead to misinterpretations if rhizosphere conditions are disregarded. Root dry weight and root-to-shoot ratio are more stable traits as compared to maximum root length and specific root length. It is recommended to evaluate a broader range of rhizosphere conditions to select tolerant genotypes.

Genetic mapping of loci affecting seedling and adult-plant resistance to powdery mildew derived from two CIMMYT wheat lines

Main conclusionPM3 and PM8 alleles carried by two CIMMYT wheat lines confer powdery mildew resistance in seedlings and/or adult plants. A stage-specific epistatic interaction was observed between PM3 and PM8.Powdery mildew is an important foliar disease of wheat. Major genes for resistance, which have been widely used in wheat breeding programs, are typically effective against only limited numbers of virulence genes of the pathogen. The main aim of this study was to map resistance loci in wheat lines 7HRWSN58 and ZWW09-149 from the International Maize and Wheat Improvement Center (CIMMYT). Doubled haploid populations (Magenta/7HRWSN58 and Emu Rock/ZWW09-149) were developed and grown in controlled environment experiments and inoculated with a composite of Blumeria graminis f.sp. tritici isolates that had been collected at various locations in Western Australia. Plants were assessed for powdery mildew symptoms (percentage leaf area diseased) on seedlings and adult plants. Populations were subjected to genotyping-by-sequencing and assayed for known SNPs in the resistance gene PM3. Linkage maps were constructed, and markers were anchored to the wheat reference genome sequence. In both populations, there were asymptomatic lines that exhibited no symptoms. Among symptomatic lines, disease severity varied widely. In the Magenta/7HRWSN58 population, most of the observed variation was attributed to the PM3 region of chromosome 1A, with the allele from 7HRWSN58 conferring resistance in seedlings and adult plants. In the Emu Rock/ZWW09-149 population, two interacting quantitative trait loci were mapped: one at PM3 and the other on chromosome 1B. The Emu Rock/ZWW09-149 population was confirmed to segregate for a 1BL·1RS translocation that carries the PM8 powdery mildew resistance gene from rye. Consistent with previous reports that PM8-derived resistance can be suppressed by PM3 alleles, the observed interaction between the quantitative trait loci on chromosomes 1A and 1B indicated that the PM3 allele carried by ZWW09-149 suppresses PM8-derived resistance from ZWW09-149, but only at the seedling stage. In adult plants, the PM8 region conferred resistance regardless of the PM3 genotype. The resistance sources and molecular markers that were investigated here could be useful in wheat breeding.

Quality traits analysis of 153 wheat lines derived from CIMMYT and China.

In order to understand the difference of quality for Chinese and CIMMYT wheat varieties (lines), we selected 153 wheat germplasm from both China and CIMMYT to explore the contribution relationship of different allelic variation combinations to wheat quality through genotyping and phenotyping, including grain hardness, polyphenol oxidase (PPO) activity, lipoxygenase (LOX) activity, yellow pigment (YP) content and protein content. In terms of flour milling quality, Chinese wheat varieties were mainly carrying Pina-D1a/Pinb-D1b, accounting for 32.0% of the total tested varieties, while the CIMMYT wheat lines were mainly carrying Pina-D1b/Pinb-D1a with 45.8% of the total collection. The distribution frequencies of subunit 1/2* and 5 + 10 were 47.0% and 42.5%, respectively, in CIMMYT varieties, however they were only 31.4% and 13.7% respectively of the Chinese wheat tested varieties. In addition, the proportion of phytoene synthase (PSY) allele, PPO allele and LOX active allele were roughly the same between Chinese and CIMMYT varieties. Based on the present study, we found that Pina gene had a greater impact on grain hardness value than Pinb gene; The influence of PPO-A1 gene on polyphenol oxidase activity was more significant than PPO-D1 gene. The high protein content of varieties mostly containing hardness genes and 1/2*/5 + 10 subunit combinations. Based on the present study, we found that the quality gene distribution of Chinese and CIMMYT varieties was quite different, for instance, the high-quality HMW-GS subunits of Chinese varieties were lower than CIMMYT lines. It will be much useful for Chinese wheat breeders to develop good quality wheat variety by crossing with 3 good strong gluten CIMMYT wheat lines by molecular marker-assisted selection.

QTL Analysis of Grain Yield-Related Traits for Terminal Heat Stress Tolerance in Wheat Using SSR Markers.

<b>Background and Objective:</b> Late sowing of wheat exposes the anthesis and grain filling stages of the crop to a terminal heat temperature stress Therefore, detecting putative QTL associated with grain yield and its attributes and identifying the most tolerant genotypes to terminal drought and heat stress across environments will be beneficial in wheat breeding programs. <b>Materials and Methods:</b> In the present study, among 49 CIMMYT wheat lines evaluated for yield and stability in eight environments, we selected the highest ten high-yielding (HYL) and the lowest ten low yielding lines (LYL) along with three wheat check cultivars (CC) for screening with eighteen previously published SSR molecular markers associated with drought and heat stress tolerance. <b>Results:</b> Two SSR markers (BARC126 and BARC11) on 7D were associated with delay heading dates under normal and late sowing dates. Likewise, the SSR markers WMC396, GWM537 and XGWM577 which were mapped on 7B, were significantly linked with grain yield-related traits under one/or both sowing dates, most of them showed desirable effects, indicating terminal heat stress tolerance. Different SSR markers viz., BARC11, XGWM132 and GWM537 showed pleiotropic effects. <b>Conclusion:</b> The SSR markers BARC186-5A, XGWM132-6B, WMC396-7B, XGWM577-7B and GWM165-4B were more prominently associated with heat tolerance by showing a desirable performance of grain yield-related traits under late sowing or across environments, some of these desirable alleles were corresponding to previously QTL in various genotypes that could be valuable in breeding for high-yield in wheat.

Cloning of the broadly effective wheat leaf rust resistance gene Lr42 transferred from Aegilops tauschii

The wheat wild relative Aegilops tauschii was previously used to transfer the Lr42 leaf rust resistance gene into bread wheat. Lr42 confers resistance at both seedling and adult stages, and it is broadly effective against all leaf rust races tested to date. Lr42 has been used extensively in the CIMMYT international wheat breeding program with resulting cultivars deployed in several countries. Here, using a bulked segregant RNA-Seq (BSR-Seq) mapping strategy, we identify three candidate genes for Lr42. Overexpression of a nucleotide-binding site leucine-rich repeat (NLR) gene AET1Gv20040300 induces strong resistance to leaf rust in wheat and a mutation of the gene disrupted the resistance. The Lr42 resistance allele is rare in Ae. tauschii and likely arose from ectopic recombination. Cloning of Lr42 provides diagnostic markers and over 1000 CIMMYT wheat lines carrying Lr42 have been developed documenting its widespread use and impact in crop improvement.

Evaluation of CIMMYT Wheat Lines under Egyptian Field Conditions to Identify New Sources of Resistance to Leaf Rust

Leaf rust caused by Puccinia triticina Eriks. is a fungal disease of wheat (Triticum aestivum L.), which causes considerable yield loss. Host resistance is the most effective and economical method to minimize yield losses caused by leaf rust. The current research was planned to evaluate the response of 93 wheat genotypes lines selected from 716 wheat genotypes delivered to Egypt by International Maize and Wheat Improvement Center (CIMMYT). These genotypes were evaluated against leaf rust resistance under field conditions at two locations i.e. Behira governorate (Itay El-Baroud Agricultural Research Station) and Menoufia governorate during three successive growing seasons i.e. 2017/2018, 2018/2019 and 2019/2020. Results of the current study showed that 47 wheat genotypes were resistant and had the lowest values of final rust severity (FRS %), average coefficient of infection (ACI) and area under disease progress curve (AUDPC). Also, these genotypes showed desirable/acceptable relative resistance index (RRI) at the two locations during the three growing seasons of the study. Therefore, we can select these genotypes as resistant lines in the breeding program for the resistance of leaf rust.

Genetic Mapping of Resistance in Hexaploid Wheat for a Quarantine Disease: Karnal Bunt.

Karnal bunt (KB) of wheat, caused by Tilletia indica, is one of the greatest challenges to grain industry, not because of yield loss, but quarantine regulations that restrict international movement and trade of affected stocks. Genetic resistance is the best way to manage this disease. Although several different sources of resistance have been identified to date, very few of those have been subjected to genetic analyses. Understanding the genetics of resistance, characterization and mapping of new resistance loci can help in development of improved germplasm. The objective of this study was to identify and characterize resistance loci (QTL) in two independent recombinant inbred lines (RILs) populations utilizing different wheat lines as resistance donors. Elite CIMMYT wheat lines Blouk#1 and Huirivis#1 were used as susceptible female parents and WHEAR/KUKUNA/3/C80.1/3∗BATAVIA//2∗WBLL1 (WKCBW) and Mutus as moderately resistant male parents in Pop1 and Pop2 populations, respectively. Populations were evaluated for KB resistance in 2015–16 and 2016–17 cropping seasons at two seeding dates (total four environments) in Cd. Obregon, Mexico. Two stable QTL from each population were identified in each environment: QKb.cim-2B and QKb.cim-3D (Pop1), QKb.cim-3B1 and QKb.cim-5B2 (Pop2). Other than those four QTL, other QTL were detected in each population which were specific to environments: QKb.cim-5B1, QKb.cim-6A, and QKb.cim-7A (Pop1), QKb.cim-3B2, QKb.cim-4A1, QKb.cim-4A2, QKb.cim-4B, QKb.cim-5A1, QKb.cim-5A2, and QKb.cim-7A2 (Pop2). Among the four stable QTL, all but QKb.cim-3B1 were derived from the resistant parent. QKb.cim-2B and QKb.cim-3D in Pop1 and QKb.cim-3B1 and QKb.cim-5B2 in Pop2 explained 5.0–11.4% and 3.3–7.1% phenotypic variance, respectively. A combination of two stable QTL in each population reduced KB infection by 24–33%, respectively. Transgressive resistant segregants lines derived with resistance alleles from both parents in each population were identified. Single nucleotide polymorphism (SNP) markers flanking these QTL regions may be amenable to marker-assisted selection. The best lines from both populations (in agronomy, end-use quality and KB resistance) carrying resistance alleles at all identified loci, may be used for inter-crossing and selection of improved germplasm in future. Markers flanking these QTL may assist in selection of such lines.

QTL Analysis and Nested Association Mapping for Adult Plant Resistance to Powdery Mildew in Two Bread Wheat Populations.

CIMMYT wheat (Triticum aestivum L.) lines Francolin#1 and Quaiu#3 displayed effective and stable adult plant resistance (APR) to Chinese Blumeria graminis f. sp. tritici isolates in the field. To elucidate their genetic basis of resistance, two recombinant inbred line (RIL) populations of their crosses with Avocet, the susceptible parent, were phenotyped in Zhengzhou and Shangqiu in the 2014–2015 and 2015–2016 cropping seasons. These populations were also genotyped with SSR (simple sequence repeat markers) and DArT (diversity arrays technology) markers. Two common significant quantitative trait loci (QTL) on wheat chromosomes 1BL and 4BL were detected in both populations by joint and individual inclusive composite interval mapping, explaining 20.3–28.7% and 9.6–15.9% of the phenotypic variance in Avocet × Francolin#1 and 4.8–11.5% and 10.8–18.9% in Avocet × Quaiu#3, respectively. Additional QTL were mapped on chromosomes 1DL and 5BL in Avocet × Francolin#1 and on 2DL and 6BS in Avocet × Quaiu#3. Among these, QPm.heau-1DL is probably a novel APR gene contributing 6.1–8.5% of total phenotypic variance. The QTL on 1BL corresponds to the pleiotropic multi-pathogen resistance gene Yr29/Lr46/Pm39, whereas the QTL on 2DL maps to a similar region where stripe rust resistance gene Yr54 is located. The QTL identified can potentially be used for the improvement of powdery mildew and rust resistance in wheat breeding.

Single-Step Genomic and Pedigree Genotype × Environment Interaction Models for Predicting Wheat Lines in International Environments.

Genomic prediction models have been commonly used in plant breeding but only in reduced datasets comprising a few hundred genotyped individuals. However, pedigree information for an entire breeding population is frequently available, as are historical data on the performance of a large number of selection candidates. The single-step method extends the genomic relationship information from genotyped individuals to pedigree information from a larger number of phenotyped individuals in order to combine relationship information on all members of the breeding population. Furthermore, genomic prediction models that incorporate genotype × environment interactions (G × E) have produced substantial increases in prediction accuracy compared with single-environment genomic prediction models. Our main objective was to show how to use single-step genomic and pedigree models to assess the prediction accuracy of 58,798 CIMMYT wheat ( L.) lines evaluated in several simulated environments in Ciudad Obregon, Mexico, and to predict the grain yield performance of some of them in several sites in South Asia (India, Pakistan, and Bangladesh) using a reaction norm model that incorporated G × E. Another objective was to describe the statistical and computational challenges encountered when developing the pedigree and single-step models in such large datasets. Results indicate that the genomic prediction accuracy achieved by models using pedigree only, markers only, or both pedigree and markers to predict various environments in India, Pakistan, and Bangladesh is higher (0.25-0.38) than prediction accuracy of models that use only phenotypic prediction (0.20) or do not include the G × E term.

Earliness in wheat: A key to adaptation under terminal and continual high temperature stress in South Asia

High temperatures are a primary concern for wheat production in South Asia. A trial was conducted to evaluate the grain yield performance of high yielding, early maturing heat tolerant CIMMYT wheat lines, developed recently in Mexico for adaptation to high temperature stresses in South Asia. The trial, comprised of 28 entries and two checks, was grown in 13 locations across South Asia and two environments in Mexico. Each location was classified by mega environment (ME); ME1 being the temperate irrigated locations with terminal high temperature stress, and ME5 as warm, tropical, irrigated locations. Grain yield (GY), thousand kernel weight (TKW), days to heading (DH) and plant height (PH) were recorded at each location. Canopy temperature (CT) was also measured at some locations. Significant differences were observed between ME for DH, PH, GY, and TKW. The cooler ME1 locations had a mean DH of 83 days, compared to 68 days mean DH in ME5. The ME1 locations had higher mean GY of 5.26 t/ha and TKW of 41.8g compared to 3.63 t/ha and 37.4g, respectively, for ME5. Early heading entries (<79 days, mean DH) performed better across all locations, with GY of 2–11% above the local checks and 40–44g TKW. Across all locations the top five highest yielding entries had 5–11% higher GY than the local checks. The early maturing CIMMYT check ‘Baj’ also performed well across all locations. In the Mexico location, CT was associated with GY, thereby suggesting that cooler canopies may contribute to higher GY under normal as well as high temperature stress conditions. Our results suggest that the early maturing, high yielding, and heat tolerant wheat lines developed in Mexico can adapt to the diverse heat stressed areas of South Asia.

Environmental Impacts of Korean and CIMMYT Wheat Lines on Protein Characteristics and Bread Making Quality

This study was conducted to compare the protein characteristics, dough rheology and bread loaf volume of Korean wheat cultivars and CIMMYT lines produced in diverse environments and to determine the genetic and environmental effects on bread making quality. Protein characteristics, including protein content and SDS-sedimentation volume, mixing properties during dough development and bread loaf volume were primarily influenced by the environment. Wheat cultivated in Jinju exhibited higher SDS-sedimentation volume based on constant protein weight and bread loaf volume than those in Suwon and Iksan. SDS-sedimentation volume based on constant protein weight, mixing time of mixograph and mixing tolerance of mixograph were positively correlated with bread volume. Korean wheat cultivars showed different allelic variations of <TEX>$Glu-1$</TEX> and <TEX>$Glu-3$</TEX> compared to CIMMYT wheat lines. Alchanmil, Keumkangmil and Tapdongmil could be suitable for bread making because these cultivars exhibited a 10 point <TEX>$Glu-1$</TEX> score. However, Korean wheat cultivars should be introduced specific alleles in <TEX>$Glu-3$</TEX> loci, including <TEX>$Glu-A3b$</TEX> or <TEX>$d$</TEX> and <TEX>$Glu-B3b$</TEX>, <TEX>$d$</TEX>, <TEX>$f$</TEX> or <TEX>$g$</TEX>, to improve gluten strength related to increase bread loaf volume.

Genetic structures of the CIMMYT international yield trial targeted to irrigated environments

International yield trials are assembled by CIMMYT to disseminate promising wheat breeding materials worldwide. To assess the genomic structure and linkage disequilibrium (LD) within this germplasm, wheat lines disseminated during 25 years of the Elite Spring Wheat Yield Trial (ESWYT) targeted for irrigated environments of the world were genotyped with the high-throughput Diversity Arrays Technology (DArT) marker system. Analyses of population structure assigned the ESWYT germplasm into five major sub-populations that are shaped by prominent CIMMYT wheat lines and their descendants. Based on genetic distance, we concluded that a constant level of genetic diversity was maintained over the years of ESWYT dissemination. Genetic distance between the individual ESWYT lines significantly increased when the ESWYT were grouped according to the differences in years of ESWYT dissemination, suggesting a systematic change in allele frequencies over time, most probably due to breeding and directional selection. By means of multiple regression analyses, 78 markers displaying a significant change in allele frequency across years were identified and interpreted as an indicator for constant selection. The markers identified were partly associated with grain yield, leaf, stem, and yellow rust and point to key genomic regions for further investigation. Large numbers of adjacent DArT marker pairs showed significant LD across the ESWYT population and within each of the five sub-populations identified. Sub-population differentiation measured by the fixation index and average genetic distance were highly correlated with LD levels, suggesting that the sub-populations themselves explain much of the LD.

Seedling and slow rusting resistances to leaf rust in CIMMYT wheat lines

CIMMYT wheat has played an important role in wheat breeding in China. Identification of leaf rust resistance genes in CIMMYT wheat is important for developing wheat cultivars with resistance to leaf rust in China. A total of 103 CIMMYT wheat lines and a set of 35 differential lines, mostly near-isogenic lines in the background of Thatcher with known leaf rust resistance genes were inoculated with 15 Chinese pathotypes of Puccinia triticina for postulating leaf rust resistance genes in CIMMYT wheats at the seedling stage. These genotypes were also planted in the field for characterization of slow rusting responses to leaf rust in the 2008-2009 and 2009-2010 cropping seasons. Four leaf rust resistance genes Lr26, Lr34, Lr42, and Lr47 were postu- lated in 46 genotypes through seedling test, pedigree analysis and molecular maker detection. Resistance gene Lr26 was present in nine accessions. Lr34 was identified in 28 lines. Lr42 was found in eleven lines and two lines might contain Lr47. Known resis- tance genes were not identified in the other 57 accessions and these lines were resistant to most of pathotypes tested. Forty-six genotypes showed slow leaf rusting resistance in the two cropping seasons. The results from seedling and field tests showed that CIMMYT wheats carry abundant effective seedling and adult plant resistance genes, and can be used in breeding resistant culti- vars for durable control of wheat leaf rust in China.

Allelic variants of phytoene synthase 1 (Psy1) genes in Chinese and CIMMYT wheat cultivars and development of functional markers for flour colour

Phytoene synthase genes influence yellow pigment (YP) content in wheat grain, and are associated with the quality of end-use products. In the present study, a suite of 217 Chinese winter wheat cultivars and 342 CIMMYT spring wheat cultivars were used to search for phytoene synthase 1 gene variations and to detect and compare their genetic effects in different genetic backgrounds. An initial focus on the Chinese winter wheat cultivars revealed four allelic variants of this gene on chromosome 7B (Psy-B1), designated as Psy-B1a, Psy-B1b, Psy-B1c and Psy-B1d. The frequencies of these four alleles were 39.6, 43.8, 15.7 and 0.9%, respectively. A co-dominant marker YP7B-1 based on a 5-bp InDel of poly C in the fifth intron of Psy-B1 amplified a 151-bp PCR fragment in accessions with the medium YP content allele Psy-B1a, and a 156-bp fragment in lower YP content accessions with Psy-B1b. Two dominant markers YP7B-2 (428 bp) and YP7B-3 (884 bp) were designed for accessions with Psy-B1c and Psy-B1d, respectively. Allele Psy-B1c was associated with high YP content, but the phenotypic effect of Psy-B1d was not determined due to the limited number of accessions. In CIMMYT spring wheat cultivars, Psy-B1a, Psy-B1b, Psy-B1d and a further allelic variant, Psy-B1e, were detected with frequencies of 50.6, 29.2, 19.6 and 0.6%, respectively. Psy-B1c was not found in the CIMMYT germplasm. However, no significant differences were detected for mean YP content among CIMMYT wheat lines with different Psy-B1 genotypes. A new allelic variant of Psy-A1, designated Psy-A1c, was identified in three CIMMYT wheat lines, and this allele was associated with higher YP content.

SSR and Pedigree Analyses of Genetic Diversity among CIMMYT Wheat Lines Targeted to Different Megaenvironments

Improved bread wheat (Triticum aestivum L.) cultivars for diverse agroecological environments are important for success in the effort to increase food production. In the 1980s, CIMMYT introduced the megaenvironment (ME) concept to breed wheats specifically adapted to different areas. Our objective was to analyze the genetic diversity among 68 advanced CIMMYT wheat lines targeted to different MEs by using 99 simple sequence repeats (SSRs) and the coefficient of parentage (COP). The average number of alleles detected was higher for the 47 genomic SSRs (5.4) than for the 52 SSRs derived from expressed sequence tags (EST) (3.3), but gene diversity between MEs was similar for both types of markers. No significant differences among the five MEs were observed for the means of SSR‐based genetic similarities (GS), calculated as 1 − Rogers' distance, and COP values. Both measures showed a low correlation (r = 0.43). High levels of genetic diversity were found within the germplasm targeted to each ME. However, principle coordinate analysis based on modified Rogers' distances did not separate the genotypes according to their targeted MEs. We conclude that presence of a single core germplasm can reflect large phenotypic differences. A sufficient number of diverse breeding lines for each ME is required because MEs generally combine various production areas. SSRs represent a powerful tool to quantify genetic diversity in wheat, but genotypic differentiation for adaptation to specific MEs in the CIMMYT program could not be proven.

SSR and Pedigree Analyses of Genetic Diversity among CIMMYT Wheat Lines Targeted to Different Megaenvironments

SSR and Pedigree Analyses of Genetic Diversity among CIMMYT Wheat Lines Targeted to Different Megaenvironments

Genetic improvement of early vigour in wheat

Grain yield potential of Australian wheat crops is often limited because of inadequate water for crop growth and grain filling. Greater early vigour, defined here as the amount of leaf area produced early in the season, should improve the water-use efficiency and yield of wheat crops grown in Mediterranean-type climates such as occurs in southern Australia. In order to maximise selection efficiency for early vigour in breeding programs, the magnitude and form of genetic variation for early vigour and its components was investigated for 2 contrasting wheat populations. The first population comprised 28 Australian and overseas wheat varieties evaluated in a serial sowing study in Canberra. The second population contained 50 random F 2:4 and F 2:6 families derived from a convergent cross of elite CIMMYT wheat lines evaluated in Canberra, and in the field at Condobolin, New South Wales. For the first population, environmental effects on leaf breadth and length, and to a lesser extent, phyllochron interval, produced significant (P &lt; 0.05) changes in leaf area. Large and significant (P &lt; 0.05) differences were observed among Australian and overseas wheats for early vigour and its components. Australian varieties were among the least vigorous of the lines tested, with a number of overseas varieties producing about 75% greater leaf area than representative Australian wheats. Increased leaf area was genetically correlated with increases in leaf breadth and length, and a longer phyllochron interval. Significant (P &lt; 0.05) genotype ´ environment interaction reduced broad-sense heritability (%) for early vigour (H ± s.e., 87 ± 26) compared with leaf breadth (96 ± 25) and length (97 ± 27). Narrow-sense heritability (%) in the second population was small for leaf area (h2 ± s.e., 30 ± 6) and plant biomass (35 ± 7), but high for leaf breadth (76 ± 14) and length (67 ± 16). Genetic correlations were strong and positive for leaf area with plant biomass, leaf breadth and length, specific leaf area and coleoptile tiller frequency, whereas faster leaf and primary tiller production were negatively correlated with leaf area. The high heritability for leaf breadth coupled with its strong genetic correlation with leaf area (rg = 0.56-0.57) indicated that selection for leaf breadth should produce genetic gain in leaf area similar to selection for leaf area per se. However, the ease with which leaf breadth can be measured indicates that selection for this character either by itself, or in combination with coleoptile tiller production, should provide a rapid and non-destructive screening for early vigour in segregating wheat populations. The availability of genetic variation for early vigour and correlated traits should enable direct or indirect selection for greater leaf area in segregating wheat populations.

An investigation of the grain yield adaptation of advanced CIMMYT wheat lines to water stress environments in Queensland. I. Crop physiological analysis

Wheat improvement in Australia has made extensive use of germplasm developed by the International Maize and Wheat Improvement Center (CIMMYT). The opportunity for further yield improvement in Queensland was investigated by comparing CIMMYT lines and Queensland cultivars in irrigated and dryland environments at three locations. CIMMYT lines were identified, with greater than 20% yield advantage in individual environments and between 15 and 20% yield advantage over the six environments. The line mean repeatability for yield was moderate (0.492), with the variance component for line by environment (L x E) interaction 4.2 times that for lines. Therefore, while the CIMMYT lines expressed considerable L x E interaction, there was scope for further yield improvement. The water stress differential between the irrigated and dryland environments at the three locations strongly influenced L x E interaction for grain yield. Pre-anthesis water stress generated more L x E interaction for grain yield than post-anthesis stress. At the two locations where pre-anthesis water stress was severe in the dryland environment, there was no association (P &gt; 0.05) between yield under irrigated and dryland conditions. However, at the location where there was little pre-anthesis stress and a degree of post-anthesis stress there was a strong association (P &lt; 0.01) between yield under irrigated and dryland conditions. Grain yield was positively associated with the yield component grain number per unit area in all environments. Grain weight showed little L x E interaction across environments and the majority of L x E interaction for grain yield resulted from L x E interaction associated with grain number per unit area. Grain number per unit area was positively associated with the component grains per fertile tiller but not tiller number per unit area. Grains per fertile tiller was in turn positively associated with total dry matter at anthesis; however, there was no direct association between total dry matter at anthesis and grain number per unit area. There was a weak association between days to anthesis and grain yield in four of the six environments.

An investigation of the grain yield adaptation of advanced CIMMYT wheat lines to water stress environments in Queensland. II. Classification analysis

The objective of this study was to use classification methodology to characterize the genotypic variation and line by environment (L x E) interaction for grain yield of a sample of advanced CIMMYT wheat lines and three local check cultivars tested over six Queensland environments. The environments were managed to differ in the magnitude of water stress they imposed on the lines at the critical developmental stage of anthesis. The grouping of lines was based on grain yield. The yield differences among the groups were investigated in terms of yield components and dry matter production and partitioning attributes. Groups of CIMMYT lines which outyielded the two groups which contained the three Queensland cultivars were identified. The yield advantage of the groups of CIMMYT lines decreased with increasing severity of water stress at anthesis and in the environment where the most severe stress was characterized there were no yield differences among the groups of lines. The yield advantage of the groups of CIMMYT lines was generally associated with a higher number of grains per unit area and in some cases a higher grain size. While phenology variation could account for some of the yield differences among the line groups there was considerable yield variation among line groups with similar phenology patterns across the environments. Additional measurements taken on the lines to characterize differences in dry matter production and the partitioning of the dry matter to yield components were not effective in explaining the yield variation among the groups of lines after the effects of phenology were taken into account. While the incidence of the large L x (water-stress) interactions encountered in this study would complicate selection for yield, the identification of groups of advanced CIMMYT lines which outyielded the Queensland cultivars in five of the six environments suggests that the L x (water stress) interactions do not preclude scope for further improvement of grain yield of wheat in Queensland.

Predicting grain yield in Australian environments using data from CIMMYT international wheat performance trials. 1. Potential for exploiting correlated response to selection

Australian wheat breeding programs are currently evaluating and using advanced breeding lines from the International Centre for Wheat and Maize Improvement (CIMMYT). A more coordinated and efficient procedure for identifying useful lines for Australian breeding programs was evaluated by assessing the potential for exploiting correlated response to selection for grain yield between CIMMYT international and Australian evaluation trials. The genetic correlation, based on 40 common lines, between average line performance across 18 international and six Australian environments was high (0.813±0.049), indicating considerable potential for exploiting correlated response to selection for broad grain yield adaptation to the Australian environments for selection on broad adaptation in the international environments. The potential to select for specific grain yield adaptation to the individual Australian environments was investigated and individual international environments were identified which expressed a higher genetic correlation with the Australian environments than did average performance over all of the international environments. Therefore, opportunity exists for Australian wheat breeders to use the principles of indirect selection to select among advanced CIMMYT wheat lines on grain yield performance in international performance trials for both broad and specific grain yield adaptation to Australian environments prior to the introduction of this material to Australia. Since genotype by environment interaction for yield in the international trials is large and its causes are not well understood, selection for specific adaptation on the results from individual trials will require further investigation of the individual relationships.