Genetic Insight into Yield-Associated Traits of Wheat Grown in Multiple Rain-Fed Environments

Background: Grain yield is a key economic driver of successful wheat production. Due to its complex nature, little is known regarding its genetic control. The goal of this study was to identify important quantitative trait loci (QTL) directly and indirectly affecting grain yield using doubled haploid lines derived from a cross between Hanxuan 10 and Lumai 14. Methodology/Principal Findings: Ten yield-associated traits, including yield per plant (YP), number of spikes per plan

Evaluation of CIMMYT conventional and synthetic spring wheat germplasm in rainfed sub-tropical environments. I. Grain yield

Hexaploid spring wheat (Triticum aestivum L.) germplasm from CIMMYT's breeding program in Mexico has assisted wheat improvement in Australia, particularly in the north-eastern region where terminal drought frequently reduces grain yield. A total of 273 conventional hexaploid and derived synthetic hexaploid spring wheats from CIMMYT, along with 15 locally adapted Australian cultivars (Oz lines), were evaluated for grain yield over four years in a total of 27 environments in Australia's north-eastern wheat region. The CIMMYT conventional spring wheats were from a Seri/Babax recombinant inbred line population (SB lines), elite entries from an International Adaptation Trial (IAT lines) introduced to Australia between 1999 and 2004 and from CIMMYT screening nurseries introduced to Australia in 2004-2005 (SW lines). Synthetic wheats (SYN lines) were also from these nurseries as well as from a separate program of synthetic wheat introductions to Australia over 2001-2004.Across all environments SB lines were the highest yielding, with 16 broadly adapted SB lines having advantages of 6-10% over seven broadly adapted Oz lines. In a subset of high yielding environments broadly adapted SB, SW and IAT lines were the highest yielding classes, with advantages of 3-8% over these broadly adapted Oz lines. Relative to older CIMMYT spring wheats in the IAT class, the more recent CIMMYT SW lines were better adapted to low yielding environments, with yield advantages of 5% over broadly adapted Oz lines, but they also had the capacity to respond to more favourable conditions. SYN lines were specifically adapted to a subset of lower yielding environments where yields of the broadly adapted synthetics were 5% higher, and up to 13% for individual lines, than that of the broadly adapted Oz lines. Our results support CIMMYT's use of synthetic wheats to improve adaptation to drier environments, and CIMMYT's current breeding strategy of sequential selection under water-stress and irrigation to improve adaptation in drier environments while retaining capacity to respond to more favourable conditions. CIMMYT germplasm has been identified that would be useful as parents in Australian breeding programs targeting rainfed environments with high probabilities of water deficit during the grain filling period. This germplasm should also be adapted globally to similar non-irrigated regions within CIMMYT's mega-environments ME1, ME4c and semi-arid to arid regions of ME5

Evaluation of CIMMYT conventional and synthetic spring wheat germplasm in rainfed sub-tropical environments. II. Grain yield components and physiological traits

CIMMYT hexaploid spring wheat (Triticum aestivum L.) germplasm has played a global role in assisting wheat improvement. This study evaluated four classes of CIMMYT germplasm (encompassing a total of 273 lines), along with 15 Australian cultivars (Oz lines) for grain yield, yield components and physiological traits in up to 27 environments in Australia's north-eastern region, where terminal drought frequently reduces grain yield and grain size.Broadly-adapted CIMMYT germplasm selected for grain yield had greater yield potential and improved performance under drought stress, being up to 5% greater yielding in High-yielding (mean yield 429gm) and 4-10% greater yielding than adapted Oz lines in Low-yielding environments (mean yield 185gm). Whilst maintaining statistically similar harvest index and spikes m compared to broadly-adapted Oz lines across all environments, sets of selected CIMMYT lines had greater canopy temperature depression (0.18-0.27°C), dry weight stem (0.20-0.37g), increased grains spike (0.8-3.4 grains), grain number m (ca. 20-800 grains), and maturity biomass (56-83gm). Compared to selected Oz lines, broadly-adapted CIMMYT lines had a smaller reduction in Low compared to High-yielding environments for these traits, especially dry weight stem, such that CIMMYT lines had ca. 25% and 10% greater dry weight stem than the Oz lines in Low- and High-yielding environment groups, respectively. Broadly-adapted CIMMYT germplasm also had slightly higher stem water soluble carbohydrate concentration at anthesis (ca. 6mgg), which contributed to their higher grain weight (ca. 0.5mggrain), and maintained an agronomically appropriate time to anthesis and plant height. Thus current CIMMYT germplasm should be useful donor sources of traits to enrich breeding programs targeting variable production environments where there is a high probability of water deficit during grain filling. However, as multiple traits were important, efficient introgression of these traits in breeding programs will be complex

Variation for and relationships among biomass and grain yield component traits conferring improved yield and grain weight in an elite wheat population grown in variable yield environments

Grain yield and kernel size (grain weight) are important industry traits for wheat in the water-limited environments of the north-eastern wheatbelt of Australia. These, and underpinning morphological and physiological traits, were evaluated in a population of recombinant inbred lines from the elite CIMMYT cross Seri/Babax, segregating for the presence of the rye translocation (T1BL.1RS). The population was examined to determine the variation among lines, relationships among traits, the extent of lineenvironment interactions, potential efficiency of direct and indirect selection, and to identify trait combinations that are associated with higher grain yield and grain weight. Transgressive segregation was observed for all traits, and lineenvironment interaction effects were frequently larger than line main effects. Across six environments ranging in yield from 202 to 660g/m, the T1BL.1RS wheat-rye translocation had a positive effect on grain weight (+3.4%) but resulted in decreased grain number per m (6.5%) and grain yield (3.1%). Realised selection responses indicated that broad adaptation was best achieved by selection for mean performance across the range of target environments. However, specific adaptation for performance in high- or low-yielding environments was best detected by direct selection in those types of environments. A group of broadly adapted Seri/Babax lines exceeded the mean of five cultivars grown commercially in the north-eastern wheatbelt by 8% for grain yield and 17% for grain weight. These Seri/Babax lines with both high grain yield and grain weight were associated with a combination of several traits: earlier flowering, reduced tillering, a greater proportion of tillers that produce grain-bearing spikes at maturity, high water-soluble carbohydrate stem reserves at anthesis, a higher proportion of competent florets at anthesis to maximise grains per spikelet leading to a high harvest index, and possibly a greater capacity to extract soil water. These results suggest a suitable ideotype for breeding high-yielding wheat cultivars with high grain weight adapted to environments with hotter, drier conditions during the post-anthesis period

Selection among genotypes in final stage sugarcane trials: Effects of time of year

Low levels of commercial cane sugar (CCS) reduce relative economic value (REV) in sugarcane. In the Australian sugarcane industry, CCS is lower early (June) compared with the completion (November) of the harvest period. Performance of sugarcane genotypes in 2 Central region series and 1 Burdekin region series of final stage selection trials was examined to determine if independent selection programs are required to select elite genotypes for 2 target periods: (a) early (before July), and (b) mature (from July on). Across series, CCS (16.83 v. 12.02% fresh cane weight) and REV (AUS3937/ha v. S3123/ha) were significantly higher in the mature than in the early period, while genotypic variance for CCS (0.76 v. 0.33), and broad-sense heritability for CCS (0.96 v. 0.86) and REV (0.79 v. 0.69), were higher in the early than in the mature period. Genetic correlations between sample times less than 3 months apart were usually ≥0.9 for CCS, but generally declined to ≤0.6 for times greater than 3 months apart. Consequently, genotype × period (early compared with mature) interaction effects on CCS affected selection decisions, especially in the Central region, and genetic improvements for CCS would be expected via specific targeting of early and mature periods. However, genotype × period interaction effects were not important for cane yield or REV, such that selection for specific adaptation to early or mature periods would not improve gains in REV across the entire harvest period. Some final stage selection trials should be harvested early in the harvest period, when heritability and genotypic variance are highest, to capture high early CCS genotypes with acceptable cane yield for recycling in breeding activities. This protocol should enhance genetic gain for early CCS and simultaneously increase REV early in the harvesting period of the Australian sugar industry

Preferential retention of chromosome regions in derived synthetic wheat lines: a source of novel alleles for wheat improvement

Synthetic hexaploid wheats (SHWs) and their synthetic derivative lines (SDLs) are being used as a means of introducing novel genetic variation into bread wheat (BW). Phenotypic information for days to flowering, height, grain weight and grain yield was collected from multiple environments for three SDL families, each with ∼50 lines, and their elite BW parents. In general, the SDLs were earlier flowering and taller with larger grain size, but similar grain yield to the BWs. The three SDL families and their SHW and BW parents were genotyped using mapped DArT (diversity arrays technology) markers. Within each SDL family, SHW-specific DArT markers were used to identify SHW-derived chromosomal regions that appeared to be preferentially retained in the SDL families, as determined by retention at frequencies >0.25, the expected frequency for Mendelian segregation. Regions on chromosomes 2BS and 7BL appeared to be preferentially retained in all three SDL families, while regions on chromosomes 1AL, 1BS, 3BS, 5AS, 5BL, and 7AS were preferentially retained in two of the three SDL families. Other regions were preferentially retained in single families only, including some regions located on the D genome. Single-marker regression analysis was performed using the preferentially retained markers and identified markers and regions that were significantly associated with one or more of the four traits measured. Comparative mapping also indicates that these preferentially retained markers and chromosome regions may co-locate with previously identified QTLs for anthesis, height, grain weight and/or grain yield. Therefore, SHWs may contain novel alleles at these loci in these regions for these traits, which may provide a selective advantage to the SDLs. This approach could provide a useful method for identifying chromosomal regions of interest with potentially novel alleles for introgression for further BW improvement

Genomic regions for canopy temperature and their genetic association with stomatal conductance and grain yield in wheat

Stomata are the site of CO2 exchange for water in a leaf. Variation in stomatal control offers promise in genetic improvement of transpiration and photosynthetic rates to improve wheat performance. However, techniques for estimating stomatal conductance (SC) are slow, limiting potential for efficient measurement and genetic modification of this trait. Genotypic variation in canopy temperature (CT) and leaf porosity (LP), as surrogates for SC, were assessed in three wheat mapping populations grown under well-watered conditions. The range and resulting genetic variance were large but not always repeatable across days and years for CT and LP alike. Leaf-to-leaf variation was large for LP, reducing heritability to near zero on a single-leaf basis. Replication across dates and years increased line-mean heritability to ∼75% for both CT and LP. Across sampling dates and populations, CT showed a large, additive genetic correlation with LP (=-0.67 to-0.83) as expected. Genetic increases in pre-flowering CT were associated with reduced final plant height and both increased harvest index and grain yield but were uncorrelated with aerial biomass. In contrast, post-flowering, cooler canopies were associated with greater aerial biomass and increased grain number and yield. A multi-environment QTL analysis identified up to 16 and 15 genomic regions for CT and LP, respectively, across all three populations. Several of the LP and CT QTL co-located with known QTL for plant height and phenological development and intervals for many of the CT and LP quantitative trait loci (QTL) overlapped, supporting a common genetic basis for the two traits. Notably, both Rht-B1b and Rht-D1b dwarfing alleles were paradoxically positive for LP and CT (i.e. semi-dwarfs had higher stomatal conductance but warmer canopies) highlighting the issue of translation from leaf to canopy in screening for greater transpiration. The strong requirement for repeated assessment of SC suggests the more rapid CT assessment may be of greater value for indirect screening of high or low SC among large numbers of early-generation breeding lines. However, account must be taken of variation in development and canopy architecture when interpreting performance and selecting breeding lines on the basis of CT