News With 'hairy roots', have scientists found a key to making plants more climate-robust?
Can you make plants more drought-resistant by exposing their tissues to specific soil bacteria in the lab? Plant scientists have known for some time that they can use this "bacterial breeding" to alter a plant's root characteristics. In ornamental horticulture, it has already led to varieties with a more compact and thus more attractive form. Whether it is also successful in making chrysanthemum, sunflower, apple and rose more climate resistant is the question that will be investigated in the new project RootsPlus during the next 3 years. "The technique is difficult and plant-dependent, but you obtain a market-ready new cultivar much faster than with other breeding techniques," says project coordinator Ellen De Keyser (ILVO).
Climate and drought are urgent challenges in agriculture and horticulture
Climate change poses many challenges to plant production. In the event of persistent drought, for example, crops will not find sufficient moisture and nutrients through their roots. Because they also lose more moisture through evaporation, they suffer from 'drought stress'. "That usually results in a growth slowdown or stagnation. More seriously, it can lead to withering that the plant does not recover from when it finally does rain. This year was an exception, but harvest and quality losses due to drought stress have become more common in recent years," says Emmy Dhooghe (ILVO RootsPlus researcher).
Soil bacteria stimulate the growth of hairy roots
Finding solutions to better arm plants against drought stress is therefore an important task for plant scientists. The soil bacterium Rhizobium rhizogenes, which is abundantly present in nature, could play an important role in this. When you put a piece of leaf or stem in a petri dish together with this bacterium, it transfers part of its DNA (the T-DNA) to the DNA of the plant, just like in nature. Under the influence of this T-DNA, the plant tissue forms a new type of root, also called 'hairy roots' because they are often very fluffy. From these hairy roots, plant scientists can then grow new plantlets, which in turn often form more elongated or finely branched roots. And that's an interesting feature in dry years.
On the left, the roots of the control plant. On the right, the roots of the modified plant: more root mass is clearly visible.
Logical link between root morphology and drought tolerance
In dry periods, plants must be able to absorb a lot of water after each short, heavy rainfall. Plants with widely branched, superficial root systems are better at this than plants with one deep taproot. Thus, altered root morphology can affect a plant's ability to take up water from the soil.
Speeding up breeding for drought-tolerance
"Through classical plant breeding, we would never be able to achieve this. Creating hairy roots is really unique to bacterial breeding (outside of GMO legislation) and in that sense represents an acceleration in breeding towards drought tolerance."
Nevertheless, it will be some time before we find drought-tolerant plants on the market that have descended from hairy roots. After all, not all in vitro grown plants develop an extensive root system, and in addition to root morphology they will also be evaluated for drought tolerance. Only the champion plants that score well in both areas will then be selected for further cross-breeding. "Depending on the crop, this can yield more climate-resistant plants within 5 to 10 years that can be directly used in breeding commercial varieties."
Also a pathway against 'soil fatigue' or 'replant disease'
RootsPlus uses chrysanthemum as a model crop for herbaceous plants, rose and apple as model plants for woody plants, and sunflower as a model plant for agricultural and industrial crops.
For apple and rose, RootsPlus poses a second research question: can bacterial engineering and the modified root system also increase the resilience of the tree or shrub to soil fatigue or 'replant disease'? In this phenomenon, roses and apple trees suffer from delayed growth and a defective root system when they are planted in a place where roses and apple trees were planted previously. The exact cause of this phenomenon is not known but one notices a disturbed morphological and physiological response of the plant to the accumulated soil life (microbiome). "We hope that the strong root growth controlled by the genes of the soil bacteria can overcome this problem."
European project ‘RootsPlus’
The ‘RootsPlus’ project started on April 1, 2021. It is a European collaboration between Germany (University of Hannover), Poland (Nicolaus Copernicus University), Romania (University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca) and ILVO ( project coordinator). In Flanders, the project is funded by VLAIO (Flanders Innovation & Entrepreneurship). ILVO cooperates with 2 companies. More info
This project RootsPlus was carried out under the second call of the ERA-NET Cofund SusCrop, being part of the Joint Programming Initiative on Agriculture, Food Security and Climate Change (Facce-JPI). SusCrop has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 771134.