Making rice resistant to weeds

Plant biologists Ronald Pierik and Rashmi Sasidharan are conducting research into rice in the Botanic Gardens to study whether they can optimise the architecture of the plant in order to compete against weeds by overshadowing them. “Did you know rice is grown under water in rice paddies because most weeds won't survive flooding? Rice plants are traditionally planted one-by-one, but that is extremely time-consuming. Farmers would rather sow rice seeds, but that would not give the plants a head start against weeds, and the crop would quickly become overgrown”, explains photobiologist Ronald Pierik from Utrecht University. 


But more and more weeds are evolving resistance to flooding. Flooding the paddies is then no longer a solution. Together with the International Rice Research Institute in the Philipines, the scientists at the Botanic Gardens are studying the ideal growing conditions for rice by experimenting with light, water, density, and different rice varieties. “For example, you can cross several strains of rice, and combine it with a different water regime. By flooding the rice paddies early, then draining them briefly before flooding them again, you might be able to kill off the weeds.” At the moment, the scientists are studying the weeds’ tolerance to flooding, and they are ‘fiddling with the knobs’ to control the plants’ reaction to shade.



Rice grows compactly, so much light reaches the soil and weeds get a chance there if the soil is not flooded. By studying the shadow reactions in plants, the researchers are trying to change this.

Plants naturally try to catch the optimal amount of sunlight, and use information about neighbouring plants to control that process. One well-known system is the registration of the ratio of red light to infra-red light. Pierik: “Plants use red light for photosynthesis, and they reflect infra-red light. Before plants begin to overshadow one another, they can observe their neighbours by registering the proportion of red light to infra-red light. They then react by speeding up the growth of stems and leaves.” The scientists are currently studying how this architecture in rice is regulated at the molecular level.


Shade alarm The model plant Arabidopsis uses a different shade alarm system, however. “Arabidopsis grows like a rosette, without a vertical structure. These plants have a very early shade alarm that reacts to touch instead of light: the leaves adapt their direction of growth when the tips of the leaves of two plants touch.” The plant scientists are now investigating which regulators from the sand rocket can be implemented in rice, to allow rice to grow in such a way that less light reaches the soil and weeds can be suppressed.

The rice study is conducted by the Plant Ecophysiology research group.