Phenotyping for Breeding and Physiological Pre-Breeding

Phenotyping has always been the cornerstone of plant breeding but until the advent of remote sensing (RS) tools, selection was largely restricted to heritable traits –phenology, height, kernel size, disease resistance, and non-negotiable complex traits including end-use quality and yield itself. However, RS allows integrative traits -that are by definition genetically complex- to be evaluated on scale that overcomes some of the disadvantages of their relatively low heritability. In particular canopy temperature is a good predictor of yield and root function under abiotic stress, and a number of spectral indices –including NDVI and water index- also show predictive power.

Recent research has shown that by migrating from ground-based to aerial phenotyping platforms, improved precision leads to increased heritability and therefore greater predictive power. Other traits that lend themselves to aerial high throughput (HTP) screening are pigments and other indices associated with photosynthesis and photo-inhibition, and water-related indices associated with hydration status of tissue. In the meantime, innovations that are in the pipeline include use of image analysis to estimate agronomic traits, and the application of vegetative indices to correct for spatial variation in large trials. Many of the RS indices mentioned, by virtue of being HTP, lend themselves well to large-scale genetic resource screening as well as genetic analysis.

However, integrative traits have less power to predict performance under high yield environments. Here, physiological breeding focuses more on the phenotype of potential parents in order to design complementary crosses, though on a smaller scale. A good example is spike photosynthesis (SPS) which is difficult to measure and as a result has been largely ignored, despite the fact that spikes intercept up to half of incident radiation during grain-filling. However, three innovations have been applied to better characterize SPS including a 360 degree LED illumination chamber for gas exchange measurement, long duration spike shading treatments and use of stable carbon isotopes analysis of grain, both of which help estimate the integrated contribution of SPS to yield.