Enhancing stomatal performance to improve CO2 uptake for photosynthesis is an important target to increase crop yields. However, a current lack of molecular markers limits breeding progress. Stomata are the primary gatekeepers for CO2 uptake for photosynthesis and water loss via transpiration, and therefore play a central role in yield determination. Although stomatal conductance (gs) and assimilation rate (A) are often highly correlated under steady-state light conditions, studies have demonstrated that under dynamic light environments (i.e. field conditions) an uncoupling between gs and A can result in sub-optimal physiological processes. In fact, stomatal responses are generally an order of magnitude slower than photosynthetic responses. Therefore, ‘speedy stomata’ in response to changes in light intensity have recently been identified as an unexploited breeding target for crop improvement. This work aims to dissect the genetic basis of optimal stomatal dynamics to facilitate molecular breeding approaches to increase wheat yield.

We will present findings from a series of experiments to detect genotypic variation in a winter wheat MAGIC population, carried out both in the greenhouse and field over two seasons. Steady-state gs and the rapidity of change in gs to a step change in light intensity were assessed in the population with direct (i.e. infra-red gas analysers, porometers) and indirect (i.e. transpirational canopy cooling) methods in the field. Canopy temperatures were measured using a drone-mounted thermal imaging camera. Under controlled environmental conditions, temporal behaviour of A, gs and water-use efficiency (iWUE = A/gs) of the population were estimated using a cutting-edge combined chlorophyll fluorescence and thermal imaging system that enabled accurate measurement of the quantum yield of photosystem II and leaf temperature. In total, up to 640 MAGIC lines were phenotyped in the field and 480 lines in greenhouse conditions.

There was significant genotypic variation (p<0.05) for most of the estimated traits. Initial analysis of the greenhouse data showed moderate heritabilities (h2 0.1-0.4). To date, genetic analyses have identified QTL, mainly related to stomatal rapidity and maximum steady-state gs. To confirm QTLs, development of near isogenic lines via use of residual heterozygosity in the MAGIC recombinant inbred lines is on-going. This work lays the foundation for marker-assisted selection for improved stomatal performance in wheat.