High Throughput Phenotyping Technology | High Throughput Phenotyping in Plant Breeding

HTP devices are separated into four categories: Field-based phenotyping platforms (FBPP), cable-suspended, satellite imaging technology, and unmanned aerial vehicles (UAV, aka drones). Each device type has its own set of pros and cons, but among the four categories, UAVs are the most flexible and convenient platform. These platforms are used to carry different sensors that can measure phenotypes. Sensors can be mechanical, chemical, or optical. However, optical sensors are the most commonly used sensors for plant phenotyping.

Like our eyes, optical sensors are instruments designed to detect specific wavelengths of light in the electromagnetic spectrum. The electromagnetic spectrum is the entire range of electromagnetic waves organized by wavelength or frequency (Fig. 4).

Figure 4. *The electromagnetic spectrum.* Humans visually sense wavelengths in the visible spectrum while UAVs can assign values to light reflectance in the visible spectrum as well as the infrared spectrum.

Reprinted from EM spectrum by P. Ronan, 2007, *Wikimedia Commons*. CC BY-SA 3.0.

Our eyes and brain are biologically designed to detect and recognize the wavelengths in what is called the visible light region of the electromagnetic spectrum. HTP sensors are engineered to measure the level of reflectance and absorption of light in the entire electromagnetic spectrum. Different sensors are sensitive to a different range of wavelengths of light (Table 1).

Table 1. Four sensors used for high throughput phenotyping and the wavelengths they detect.
Sensor	Wavelengths
RGB	475-668 nm
Multispectral	RGB (475-668 nm) + Red Edge (717 nm) + NIR (842 nm)
LiDAR	905 nm
Thermal	7,500-13,500 nm

This range of wavelength detection sensitivities provide plant biologists and plant breeders combinations of sensors to test which can measure differences in how plants interact with (absorb / reflect) light. The question is ‘do these light reaction differences relate to the traits the plant breeder needs to evaluate?’.