With the scanner, into the terra incognita: How do you watch roots grow?

The depths of the ocean are probably better explored than the finely branched roots of plants in the ground. It is the roots that decide how well maize, beets or other plants absorb water or nutrients from the soil. And therefore, to some extent, how much the farmer has to irrigate or fertilise. Therefore, roots are an important factor in the breeding of drought-tolerant or nitrogen-efficient new plant species.

How well do plants cope with stress?

In the KWS research department, the Australian Benjamin Gruber and his colleagues explain how root growth can be observed, assessed and quantified. His goal is to test hundreds of plants in a short period of time, to see how well they can cope with abiotic stress such as drought or lack of nutrients. This is one of the prerequisites for identifying new genes in plants that ensure stable yields and drought tolerance. Both are major breeding goals at KWS.

Observing roots and their growth in detail is by no means trivial: One square metre of grain field often contains 50 to 90 kilometres of roots (about 40 to 60 kilometres for maize, and 20 to 50 kilometres for sugarbeet). Sugarbeet roots protrude up to five metres deep in the Earth. The finest root hairs are consistently thinner than a human hair. How can you achieve an accurate picture?

Dig, rinse and measure

A proven approach with maize follows the comparatively simple, so-called "shovelomics" approach: The plant with the root still on it, is simply dug up during this "shovel research" and the soil is thoroughly rinsed off. Then, the root can be optically measured with cameras and software. From multiple images, specialists in image analysis and bioinformaticians calculate the number and thickness of the roots and their angle relative to the stem of the plant.

"KWS is currently creating a new toolbox to capture root growth on a large scale. We test new processes and refine what has been proven. Later, we need to understand which plant with which genetic makeup grows in which soil, and with which nutrient and water supply," says Gruber. This costs time and money. Both are investments in the future of a company that has existed for more than 160 years and continues to offer growers high-yielding varieties. Family-oriented KWS spends about 17 percent of its turnover on research.

Breeding requires accurate observation

Exact observation of plant traits, with the purpose of deriving indications for breeding, is as old as agriculture itself. For example, the first farmers sowed from the thickest grains of the previous year for the following year. Gregor Mendel observed the colour and shape of peas to establish his inheritance rules based on these results. With regard to the visible and measurable properties of plants, biologists talk about phenotypes.

Ben Gruber's approach is similar to other phenotyping projects at KWS. KWS research experts collect data in the environment, either with drone-based cameras or underground scanners. The images are collated on the computer and automatically analysed to give new clues to the breeders. "All this has to work on an industrial scale, in wind and rain, in mud and in drought - not just in a lab or with 20 plants. Plant breeding is always a question of large numbers, and thousands of plants must be evaluated," explains Gruber, before he returns to the statistical analysis of his data.