Direct measurements deliver physical properties of the measured object, such as dimensions, morphology, or reflectance in certain wavelength ranges. Indirect measurements address growth and biomass accumulation together with physiological traits that indicate stress and disease responses, water and nutrition relations, or photosynthetic capacity. They are frequently sample specific and require precise analysis.
Indirect measurements usually require calibration experiments and mathematical processing to derive results. The table opposite shows which sensors can be used to measure specific traits.
Non-invasive measurements with cameras and scanners capture a broad variety of traits in above-ground plant parts such as shoots, leaves, flowers or fruits. Different sensor types address the electromagnetic spectrum comprising the visual light and beyond and thereby record a broad range of properties.
Non-invasive measuring organs that usually grow below ground, e.g. roots or tubers, is more challenging than measuring the above-ground parts. Specific experimental setups enable exposing such organs to cameras, e.g. the use of transparent pots.
So far, phenotyping of below-ground organs is mainly conducted with RGB-cameras. However, other types of cameras can also deliver meaningful data, particularly when exploring stress responses.
Non-invasive characterisation enables scientists to categorise seeds before sowing, and thus carry out seed-to-plant tracking, and to analyse seed after harvest. Germination tests can also be conducted to measure viability.
Indirect measures of physiological properties provide insights into the quality of the seeds and add value to applied seed testing processes.
Phenotypic data relating to non-plant organisms is of great interest because many of them are plant-associated and can be beneficial or pathogenic to the food chain.
Besides measuring dimensions and morphology, other traits such as movement, feeding or physiological characteristics can be measured. Such data is used for analysing the interaction of organisms with plants, and for developing pesticides.