Grass inflorescences produce grains, which are directly connected to our food. In grass crops, yields are mainly affected by grain number and weight; thus, understanding inflorescence shape is crucially important for cereal crop breeding. In the last two decades, several key genes controlling inflorescence shape have been elucidated, thanks to the availability of rich genetic resources and powerful genomics tools. In this review, we focus on the inflorescence architecture of Triticeae species, including the major cereal crops wheat and barley. We summarize recent advances in our understanding of the genetic basis of spike branching, and spikelet and floret development in the Triticeae. Considering our changing climate and its impacts on cereal crop yields, we also discuss the future orientation of research.

/pdf/form-follows-function-in-triticeae-inflorescences-lnl78umk.pdf

Form follows function in Triticeae inflorescences

Modern wheat (Triticum aestivum L.) cultivars have a free-threshing habit, which allows for easy manual or mechanical threshing. However, when harvesting is delayed or extreme weather events occur at harvest time, grain shattering can cause severe loss of harvestable yield. In the past, grain size was considered a predisposing factor as large, plump kernels can lead to buckling and breaking of the outer glume, but the correlation between glume strength and shattering is not strong in modern wheat, and it is hypothesised that there may be other genetic mechanisms. Data from two bi-parent populations and a wheat diversity panel were analyzed to explore the underlying genetic basis for grain shattering observed in multiple field experiments through quantitative trait loci (QTL) analysis. Grain shattering had a significant and negative association with grain yield, irrespective of populations and environments. The correlation with plant height was positive in all populations, but correlations with phenology were population specific, being negative in the diversity panel and the Drysdale × Waagan population, and positive in the Crusader × RT812 population. In the wheat diversity panel, allelic variations at well-known major genes (Rht-B1, Rht-D1 and Ppd-D1) showed minimal association with grain shattering. Instead, the genome-wide analysis identified a single locus on chromosome 2DS, which explained 50% of the phenotypic variation, and mapping to ~ 10 Mb from Tenacious glume (Tg) gene. In the Drysdale × Waagan cross, however, the reduced height (Rht) genes showed major effects on grain shattering. At the Rht-B1 locus, the Rht-B1b allele was associated with 10.4 cm shorter plant height, and 18% decreased grain shattering, whereas Rht-D1b reduced plant height by 11.4 cm and reduced grain shattering by 20%. Ten QTL were detected in the Crusader × RT812, including a major locus detected on the long arm of chromosome 5A. All the QTL identified in this population were non-pleiotropic, as they were still significant even after removing the influence of plant height. In conclusion, these results indicated a complex genetic system for grain shattering in modern wheat, which varied with genetic background, involved pleiotropic as well as independent gene actions, and which might be different from shattering in wild wheat species caused by major domestication genes. The influence of Rht genes was confirmed, and this provides valuable information in breeding crops of the future. Further, the SNP marker close to Tg on chromosome 2DS should be considered for utility in marker-assisted selection. 

/pdf/natural-variation-and-genetic-loci-underlying-resistance-to-1vd1oy22.pdf

Natural variation and genetic loci underlying resistance to grain shattering in standing crop of modern wheat

Abstract Grain shattering in standing crops of wheat ( Triticum aestivum L.) is estimated to account for up to 17% loss of harvestable yield. In this study, we analysed data from two bi-parent populations and a wheat diversity panel to explore the underlying genetic basis for grain shattering observed in multiple field experiments through quantitative trait loci (QTL) analysis. Grain shattering had a significant and negative association with grain yield, irrespective of populations and environments. The correlation with plant height was positive in all populations, but correlations with phenology was population-specific, being negative in the diversity panel and the Drysdale × Waagan population, and positive in the Crusader × RT812 population. In the wheat diversity panel, allelic variations at well-known major genes ( Rht-B1, Rht-D1 and Ppd-D1 ) showed minimal association with grain shattering. Instead, the genome-wide analysis identified a single locus on chromosome 2DS, which explained 50% of the phenotypic variation, and mapping to ~10 Mb from Tenacious glume, Tg gene. In the Drysdale × Waagan cross, however, the reduced height ( Rht ) genes showed major effects on grain shattering. At the Rht-B1 locus, the Rht-B1b allele was associated with 10.4 cm shorter plant height, and 18% decreased grain shattering, whereas Rht-D1b reduced plant height by 11.4 cm and reduced grain shattering by 20%. Ten QTL were detected in the Crusader × RT812, including a major locus detected on the long arm of chromosome 5A. All the QTL identified in this population were non-pleiotropic, as they were still significant even after removing the influence of plant height. These results indicated a complex genetic system for grain shattering in modern wheat, which varied with genetic background, involved pleiotropic as well as independent gene actions, and which might be different from shattering in wild wheat species caused by major domestication genes. 

https://www.researchsquare.com/article/rs-2583943/latest.pdf

Pleiotropic and independent genetic loci underlie resistance to grain shattering in standing crop of modern wheat

Abstract Key message A major QTL on chromosome arm 4BS was associated with reduced spike shattering and reduced plant height in coupling phase, and a second major QTL associated with reduced spike shattering was detected on chromosome arm 5AL in the same wheat variety Carberry. Abstract Spike shattering can cause severe grain yield loss in wheat. Development of cultivars with reduced shattering but having easy mechanical threshability is the target of wheat breeding programs. This study was conducted to determine quantitative trait loci (QTL) associated with shattering resistance, and epistasis among QTL in the populations Carberry/AC Cadillac and Carberry/Thatcher. Response of the populations to spike shattering was evaluated near Swift Current, SK, in four to five environments. Plant height data recorded in different locations and years were used to determine the relationship of the trait with spike shattering. Each population was genotyped and mapped with the wheat 90 K Illumina iSelect SNP array. Main effect QTL were analyzed by MapQTL 6, and epistatic interactions between main effect QTL were determined by QTLNetwork 2.0. Correlations between height and shattering ranged from 0.15 to 0.49. Carberry contributed two major QTL associated with spike shattering on chromosome arms 4BS and 5AL, detected in both populations. Carberry also contributed two minor QTL on 7AS and 7AL. AC Cadillac contributed five minor QTL on 1AL, 2DL, 3AL, 3DL and 7DS. Nine epistatic QTL interactions were identified, out of which the most consistent and synergistic interaction, that reduced the expression of shattering, occurred between 4BS and 5AL QTL. The 4BS QTL was consistently associated with reduced shattering and reduced plant height in the coupling phase. The present findings shed light on the inheritance of shattering resistance and provide genetic markers for manipulating the trait to develop wheat cultivars. 

/pdf/main-effect-and-epistatic-qtl-affecting-spike-shattering-and-3jmh9zt2.pdf

Main effect and epistatic QTL affecting spike shattering and association with plant height revealed in two spring wheat (Triticum aestivum L.) populations

Lasse Livia

Papers

Main effect and epistatic QTL affecting spike shattering and association with plant height revealed in two spring wheat (Triticum aestivum L.) populations