Symbiosis for more sustainable rice production

CRAG and IRTA researchers demonstrate that symbiosis with arbuscular mycorrhiza fungi makes rice plants more productive and disease resistant, paving the way for a greener agriculture

A new paper published in ‘Rice’ magazine led by researchers at the Center for Research in Agrigenomics (CRAG) reveals that rice plants in symbiosis with arbuscular mycorrhizal fungi show increased growth, productivity and resistance to pyriculariosis, a devastating fungal disease. The results open up new possibilities for improving rice yields and reducing the use of fungicides. The researchers of IRTA Mar Català, from the Sustainable Extensive Crops programme, and Maite Martínez, from the Marine and Continental Waters programme, have participated in the article.

Arbuscular mycorrhiza is a fungus that establishes symbiosis with the roots of most land plants, improving their nutrition and resistance to pathogens. Until now, the effects of arbuscular mycorrhiza on rice plants, the world’s most important cereal crop, have been little studied.

Symbiosis is a mutually beneficial relationship for the organisms involved, and this strategy is already used to improve the production of many relevant crops such as wheat, oats and most legume species. Traditionally it was thought that plants grown in aquatic environments such as rice, which is mainly cultivated in flooded fields, did not establish symbiosis with arbuscular mycorrhizae. Currently, different studies have shown that this association does in fact occur, and recent work led by Sonia Campo, postdoctoral researcher at CRAG, uncovers that the symbiosis between mycorrhiza and rice can increase the yield of rice plants grown in flooded fields.

Testing and methodology

As part of the European project GreenRice, which seeks to develop a more sustainable and environmentally friendly rice cultivation system, researchers studied the effect of symbiosis on twelve widely used rice varieties in Europe. Under greenhouse conditions, rice plants were inoculated with two different mycorrhizal species, and results showed that most varieties grew more after the treatment. In parallel, the resistance of the inoculated plants to the widespread blast fungus Magnaporthe oryzae was also tested.

“After inoculating the plants and exposing them to the pathogenic fungus, we observed that in general the symbiosis protected the plants from infection. Still, in the Maratelli variety, which is very susceptible to the disease, inoculation had a negative effect. These results indicate that the symbiosis has great potential to improve blast resistance, but its effects must be evaluated on a case-by-case basis depending on the variety” explains Sonia Campo, project leader and first author of the article.

Thanks to the collaboration with expert agronomy researchers of IRTA, further tests were carried out on conventional cultivation systems. The experiments implemented in the paddy fields of the Ebro Experimental Station, a geographical area with a long history of rice cultivation, revealed that the inoculation of the fungus improved up to 40% the productivity of rice plants, mainly due to the increase in the number of panicles that contain the grains. This substantial yield increase demonstrates that the symbiosis is functional under flood conditions, and also evidences that inoculation with arbuscular mycorrhiza is a promising strategy that could be implemented in the fields.

In the light of the International Year of Plant Health proclaimed by the United Nations, this new research takes on special relevance as it opens up the possibility of using symbiosis with arbuscular mycorrhiza as a strategy to improve rice yield and blast resistance, promoting a more sustainable agriculture. “Our results suggest an alternative to the excessive and inappropriate use of fertilizers and pesticides, which has arisen environmental problems in many rice-growing areas,” adds Campo.

This work is a collaboration between researchers from the Institute of Agrifood Research and Technology (Ebro Experimental Station and IRTA Sant Carles de la Ràpita) and the Centre for Research in Agricultural Genomics (CRAG). The research has been supported by the GreenRice FACCE-JPI project, funded by the National Institute for Agricultural and Food Research and Technology (INIA), and financed by the Spanish Ministry of Science, Innovation and Universities, the State Research Agency and the European Regional Development Fund (ERDF).