Challenges and Opportunities for High-Throughput Phenotyping of Leaf Angle and Photosynthetic Rate Under Abiotic Stress.

Yield is determined by the plant’s capacity to capture light energy and utilize it to fix CO₂ into complex organic compounds. It is now fully recognized that the much needed increases in crop yield to meet future global demands for food, feed, fiber and fuel would have to largely come from manipulations of the photosynthetic capacity of plant species. This capacity is mostly determined by both the biochemical process of carbon fixation and the arrangement of leaves throughput the plant. Any environmental stress will limit the amount of fixed CO₂, and trigger photoprotection mechanisms to dissipate or avoid absorption of excess energy that might cause damage to cells and the plant as a whole. We have dissected the complex genetic architecture that controls the photosynthetic capacity of Sorghum bicolor under cold and drought stress and, we have gained an understanding of the challenges associated with phenotyping traits of medium to low heritability. Additionally, our investigation of the natural variation in leaf angle throughout the canopy suggests that this trait is under independent genetic control at different levels of the canopy. Therefore, the recently proposed plant ideotype to maximize carbon fixation and yield, called “smart canopy”, represents a new challenge that must be overcome by reconsidering and redesigning effective phenotyping and breeding strategies to discover and manipulate genes that control canopy architecture and photosynthetic capacity.