Exploring genetic diversity for grain partitioning traits to enhance yield in a high biomass spring wheat panel

© 2020 Breeding to raise yield potential through enhancing photosynthesis will have limited impact unless harvest index (HI: proportion of above-ground biomass as grain yield) is maintained or ideally increased. Boosting grain dry matter (DM) partitioning will require increased allocation of assimilates to sink organs to enhance spike growth. A high biomass spring wheat panel of 150 genotypes encompassing elite, landrace-derived and synthetic-derived lines was grown under yield potential conditions in two seasons in NW Mexico. Results showed that the incorporation of landrace-derived and synthetic-derived backgrounds into elite lines resulted in higher expression of above-ground biomass (AGDM), leaf lamina and stem DM partitioning at anthesis. However, no grain yield advantage was observed over elite lines, due to lower grain number per unit area (GN) and decreased harvest index (HI). Positive linear associations were found among spike fertility-related traits - fruiting efficiency (grains per unit of spike DM at anthesis; FE), GN and HI - which were, in turn, related positively with grain yield (GY). Stem-internode 3 length and internode 3 DM partioning were negatively associated with spike partitioning index (SPI: ratio of spike DM to total above-ground DM at anthesis) and GN, suggesting an enhanced competition for assimilates between the spike and stem internode 3 during stem elongation. Within-spike DM partitioning analysis (glume, lemma, palea, rachis, awn) showed decreased partitioning to awns was associated with increased FE and thousand grain weight (TGW). While the use of exotic material can enhance biomass, special attention needs to be paid in the selection for novel DM partitioning traits that raise HI and GN coming from the elite genepool. The selection for grain partitioning traits in wheat breeding combined with sources expressing high biomass can potentially allow breeders to increase grain carbon assimilation that will deliver higher yields

Genetic analysis of physiological traits to increase grain partitioning in high biomass cultivars in wheat (Triticum aestivum L.)

Wheat (Triticum spp.) is the second most grown crop in the world, being used as a raw ingredient in different foods making this cereal an essential component of the global food security. FAO estimates that for 2050, the global population could reach between 9.3 to 10 billion people (Peña-Bautista et al., 2017). The current global rate of yield increase in wheat is approximately 1% per year (FAOSTAT, 2013); however, to meet predicted future demand and avoid price hikes, taking into consideration unpredictable climate, genetic gains in grain yield potential are required of 1.5% per year (Fischer & Edmeades, 2010). To achieve this, it is essential to expand current understanding of how physiological traits are associated with genetic gains in yield potential and to adopt phenotypic and genotypic approaches to increase crop productivity (Aisawi et al., 2015). On this thesis the overall objective was to identify grain partitioning traits and genomic regions associated to maximize yield potential in high biomass elite backgrounds. With the use of a high biomass spring wheat association panel in NW Mexico (High Biomass Association Panel: HIBAP) and a doubled-haploid winter wheat population (Savannah x Rialto DH: SxR DH) in the UK. Field results over two seasons (Y15: 2015-15 & Y16: 2016-17) confirmed that spike partitioning index (SPI: spike dry matter / above-ground dry matter) at seven days after anthesis (GS65) and fruiting efficiency (FE: grain number / spike dry matter at GS65+7d) were positively associated with harvest index (HI: portion of biomass partitioned into grain) and grain number per m2 (GN), which in turn (HI and GN) were linearly related to grain yield. Higher SPI and HI were correlated with a shorter length of stem internode 2 (internode below peduncle) and internode 3 and reduced dry-matter partitioning to stem internode 2 and internode 3. Detailed within spike dry-matter (DM) partitioning analysis at GS65+7d revealed that FE was associated with decreased awn DM partitioning and lower rachis DM partitioning with higher grain weight (GW) and grain yield (GY). Therefore, selecting for these traits would contribute to maximising SPI and FE and, thus, HI and GN. Different molecular analysis were used within each experiment (panel/DH) depending on the sequencing data available. For the spring wheat high biomass association panel (HiBAP) using the 35K breeders’ array it was possible to identify genetic regions for grain partitioning traits on chromosomes 1A, 2B, 5A, 6A, 6B and 7A. These regions allowed the identification of candidate genes for grain partitioning traits for validation in further studies. On the other hand, for the DH winter wheat population (SxR DH) stable quantitative trait loci (QTLs) related to spike fertility and internode lengths were found on 3A, 6A and 6D using a SNP map based on KASP assays which will be useful for further fine-mapping studies. In order to test further that shortening internodes 2 and 3 (from terminal spikelet initiation to anthesis) enables more assimilates to be partitioned to the spike during stem elongation and spikelet development (pre-anthesis stage) increasing HI an experiment was carried out where plant growth regulator (PGR: Moddus 250EC) was applied as soon as the second internode was at least one centimetre (GS31-2) in 12 genotypes of the HiBAP during one season (Y17: 2016-17). Results suggested that using the adequate concentration and timing of application of PGR is possible to reduce internode lengths but further study is needed in order to make definite conclusions on effects on HI

Genetic analysis of physiological traits to increase grain partitioning in high biomass cultivars in wheat (Triticum aestivum L.)

Wheat (Triticum spp.) is the second most grown crop in the world, being used as a raw ingredient in different foods making this cereal an essential component of the global food security. FAO estimates that for 2050, the global population could reach between 9.3 to 10 billion people (Peña-Bautista et al., 2017). The current global rate of yield increase in wheat is approximately 1% per year (FAOSTAT, 2013); however, to meet predicted future demand and avoid price hikes, taking into consideration unpredictable climate, genetic gains in grain yield potential are required of 1.5% per year (Fischer & Edmeades, 2010). To achieve this, it is essential to expand current understanding of how physiological traits are associated with genetic gains in yield potential and to adopt phenotypic and genotypic approaches to increase crop productivity (Aisawi et al., 2015). On this thesis the overall objective was to identify grain partitioning traits and genomic regions associated to maximize yield potential in high biomass elite backgrounds. With the use of a high biomass spring wheat association panel in NW Mexico (High Biomass Association Panel: HIBAP) and a doubled-haploid winter wheat population (Savannah x Rialto DH: SxR DH) in the UK. Field results over two seasons (Y15: 2015-15 & Y16: 2016-17) confirmed that spike partitioning index (SPI: spike dry matter / above-ground dry matter) at seven days after anthesis (GS65) and fruiting efficiency (FE: grain number / spike dry matter at GS65+7d) were positively associated with harvest index (HI: portion of biomass partitioned into grain) and grain number per m2 (GN), which in turn (HI and GN) were linearly related to grain yield. Higher SPI and HI were correlated with a shorter length of stem internode 2 (internode below peduncle) and internode 3 and reduced dry-matter partitioning to stem internode 2 and internode 3. Detailed within spike dry-matter (DM) partitioning analysis at GS65+7d revealed that FE was associated with decreased awn DM partitioning and lower rachis DM partitioning with higher grain weight (GW) and grain yield (GY). Therefore, selecting for these traits would contribute to maximising SPI and FE and, thus, HI and GN. Different molecular analysis were used within each experiment (panel/DH) depending on the sequencing data available. For the spring wheat high biomass association panel (HiBAP) using the 35K breeders’ array it was possible to identify genetic regions for grain partitioning traits on chromosomes 1A, 2B, 5A, 6A, 6B and 7A. These regions allowed the identification of candidate genes for grain partitioning traits for validation in further studies. On the other hand, for the DH winter wheat population (SxR DH) stable quantitative trait loci (QTLs) related to spike fertility and internode lengths were found on 3A, 6A and 6D using a SNP map based on KASP assays which will be useful for further fine-mapping studies. In order to test further that shortening internodes 2 and 3 (from terminal spikelet initiation to anthesis) enables more assimilates to be partitioned to the spike during stem elongation and spikelet development (pre-anthesis stage) increasing HI an experiment was carried out where plant growth regulator (PGR: Moddus 250EC) was applied as soon as the second internode was at least one centimetre (GS31-2) in 12 genotypes of the HiBAP during one season (Y17: 2016-17). Results suggested that using the adequate concentration and timing of application of PGR is possible to reduce internode lengths but further study is needed in order to make definite conclusions on effects on HI