**Monitoring Photosynthesis by** *In Vivo* **Chlorophyll Fluorescence: Application to High-Throughput Plant Phenotyping**

Jorge Marques da Silva

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/62391

#### **Abstract**

In spite of the decrease in the rate of population growth, world population is expected to rise from the current figure (slightly above to 7.2 billion) to reach 9.6 billion in 2050. There is therefore a pressing need to increase food production. Since most of the best arable lands are already under production, expanding the agricultural areas would have negative impacts on important natural areas. Thereby, increasing the productivity of the current agricultural areas is the chief objective of agronomical planners, and planting more productive and better adapted plant varieties is crucial to achieve it. In fact, plant breeding is at the forefront of concern of both agronomists and plant biologists. Plant breeding is a millenary activity that deeply changed our world. However, the use of molecular biology techniques jointly with informatics capabilities—giving rise to the omics techniques deeply accelerated plant breeding, providing new and better plant varieties at an increased pace. The advances in genomics, though, far by-passed the advances in phenomics, and so there is a rising consensus among plant breeders that plant phenotyping is a bottle‐ neck to advancing plant breeding. Therefore, a range of international initiatives in highthroughput plant phenotyping (HTPP) are at course, and new automated equipment is being developed. Phenotyping plants, however, is not a simple matter. To begin with, it has to be decided which parameters to measure in order to extrapolate to the desired goals, plant resistance and plant productivity. For this, as well as for plant breeding, an indepth knowledge of plant physiology is required. Photosynthesis has been considered as a good indicator of overall plant performance. It is the only energy input in plants and thereby impacts all aspects of plant metabolism and physiology. The cumulative rate of photosynthesis over the growing season is the primary determinant of crop biomass. It largely determines the redox state of plant cells, and therefore, it is at the core of regulatory networks. Therefore, assessing photosynthesis and the photosynthetic apparatus plays a core role on plant phenotyping. Nevertheless, high-throughput phenotyping de‐ mands very rapid measurements, and consequently the most common method of photosynthesis measurement—the infra-red gas analysis—is not well suited for this

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purpose. On the contrary, the techniques based on *in vivo* chlorophyll (Chl) a fluores‐ cence measurements are perfectly fit. In this chapter, an historical perspective on the development of *in vivo* Chl a measurement is briefly addressed. Then, the state of the art of the fluorescence-based techniques of photosynthesis assessment is presented, and their potential use in HTPP is evaluated. Finally, the current use of these techniques in the main systems of phenotyping is surveyed.

**Keywords:** photosynthesis, photochemistry, chlorophyll fluorescence, optical techni‐ ques, plant phenomics, high-throughput plant phenotyping
