High throughput phenotyping platforms (HTPPs) are increasingly adopted in plant breeding research due to developments in sensor technology, unmanned aeronautics and computing infrastructure. Most of these platforms rely on indirect measurement techniques therefore some physiological traits may be inaccurately estimated whilst others cannot be estimated at all. Unfortunately, existing methods of directly measuring plant physiological traits, such as photosynthetic capacity (Amax) and canopy light environment, have low throughput and can be prohibitively expensive, creating a bottleneck in the breeding pipeline. We have addressed this issue by developing new low-cost enhanced-throughput phenotyping tools to directly measure physiological traits of wheat (Triticum aestivum). Our eight-chamber multiplexed gas exchange system, “OCTOflux”, can directly measure Amax with 5-10 times the throughput of conventional instruments, whilst our handmade ceptometers, “PARbars”, allow us to monitor the canopy light environment of many plots simultaneously and continuously across a diurnal cycle. By custom-building and optimising these systems for enhanced throughput we have kept costs to a minimum, with OCTOflux costing roughly half that of commercially available single-chamber gas exchange systems and PARbars costing approximately 95% less than commercial ceptometers. We recently used these tools to identify variation in the distribution of Amax relative to light availability in 160 diverse wheat genotypes grown in the field. In a two-week measurement campaign we measured Amax in over 1300 leaves with OCTOflux and phenotyped the diurnal light environment of 418 plots using 68 PARbars. These tools could be readily modified for use with any plant functional type and also be useful in validating emerging HTPPs that rely on remotely sensed data to estimate photosynthetic parameters.
Wheat yield is limited by carbohydrate supply to the filling grain, which in turn depends on whole- canopy photosynthesis. Pre-breeding for photosynthetic traits typically focuses on traits of sun- exposed leaves in the upper canopy. However, potentially far greater gains could to be made by focusing on the distribution of photosynthetic nitrogen, and photosynthetic capacity (PC), among different canopy layers. A vast body of literature, overlooked in crop pre-breeding, shows that whole-canopy photosynthesis is substantially reduced by inefficient vertical distribution of PC in relation to irradiance: specifically, upper-canopy leaves tend to have too little photosynthetic N, and lower-canopy leaves tend to have too much. Redistribution of this capacity could increase canopy carbon uptake and NUE by nearly 20% without affecting the total supply of N available for grain filling.
We propose to identify variation in the efficiency of canopy PC distribution, coupled to yield, by applying a novel and innovative rapid phenotyping screen for canopy PC distribution to a set of 310 diverse wheat genotypes, including lines in agronomically acceptable backgrounds developed from wild wheat, wheat relatives and ancestors, and all parental materials. We will then characterise canopy physiology and structure in detail for a subset of the most contrasting genotypes to identify key underlying traits and genetic markers, and deliver the resulting knowledge, germplasm and tools to our partners in the breeding industry in Australia and India, CIMMYT and to the IWYP.
T. Buckley, 2017