Capturing Photosynthetic Traits from the Progenitors of Wheat

Bottlenecks exist in raising wheat yield, which are associated with the constriction of available genetic diversity in the modern wheat gene pool and difficulties in improving photosynthesis during the growing season. Using a range of phenotyping techniques including portable infrared gas analysers, a collection of field grown progenitor wheat species and modern wheat varieties were screened for traits linked to the supply and demand components of flag leaf photosynthesis. Two Triticum dicoccoides (AABB) individuals had high rates of flag leaf photosynthesis, driven by enhanced characteristics that facilitated the supply of CO2 to the sites of carboxylation, including high stomatal and mesophyll conductance. Progeny formed through tetraploid and hexaploid crossing carried introgressions from these T. dicoccoides and were screened in a subsequent field trial. Although per unit CO2 assimilation was increased in the progeny, flag leaf area was decreased, leading to an overall lower CO2 assimilation per flag leaf. The results highlighted the negative trade-off between flag leaf area and CO2 assimilation rate. Furthermore, a yield penalty was observed in the progeny associated with linkage drag from the wild progenitors. The progenitor individuals had higher CO2 assimilation per ear than cultivated bread wheat, most likely driven by awn presence. These findings led to an investigation of how awn presence influences ear and flag leaf photosynthesis, and thus overall grain yield, using pairs of awned and unawned Near Isogenic Lines derived from Synthetic Hexaploid Wheat (SHW NILs). Results showed that while awn presence is linked to increased ear photosynthesis, in some SHW NIL pairs there was a trade-off with flag leaf CO2 assimilation. During this field trial, 4 of the 5 unawned counterparts of each SHW NIL pair had higher grain yield than the awned individuals. However, this trend was not consistent over multiple years and locations. A genome-wide association study (GWAS) was used to identify Single Nucleotide Polymorphisms (SNPs) strongly linked to the presence of awns in a larger panel of SHW. Based on these results and examples in literature, theoretical ideotypes were formed for targeted environments. To map proxies for ideotype traits, a novel mapping population was created from two tetraploid Triticum dicoccum lines. The population was genotyped using a high density SNP array and a new genetic linkage map was created. Quantitative trait loci were identified and mapped, to aid the introgression of desirable traits from a tetraploid background into hexaploid wheat.

A BBSRC funded PhD (https://bbsrcdtp.lifesci.cam.ac.uk/).