A new collaborative study by researchers at University of Calcutta and University of Kalyani has found that a close symbiotic relationship between three species — a plant, a fungus, and bacteria — can be harnessed to promote the growth of rice plants by allowing them to take up more nitrogen from the environment.
India is largely dependent on nitrogen-containing fertilizers for agriculture. Staple crops like rice that have a high requirement of organic nitrogen can take up only 30% of fertilizer-derived nitrogen for their use while 70% remains in the soil or seeps into the groundwater and nearby water bodies. This causes water pollution and adversely affects the ecosystem and environment.
A delicate balance of multiple nutrients is required for proper growth of crops. Indiscriminate use of nitrogenous fertilizers can make soils super-rich in nitrogen but at the cost of other elements important for crop growth, which become diminished in comparison. This can make soil unfit for further agricultural use.
One solution is for farmers to carry out precision farming, which is management of crops using information technology (IT) to make sure that the crops and soil receive exactly what they need for optimum growth and productivity. Unfortunately, due to lack of adequate resources for farmers to practice precision farming, we need to look for alternate solutions that are practical (cost-effective and easy to implement in large-scale) in a developing nation like ours.
In nature, there are examples of how mutually beneficial friendships (called symbiotic relationships) between species help combat nutrient insufficiency. For example, beans and peas harbour natural nitrogen-fixing bacteria (like rhizobia called diazotrophs) in their roots that have the ability to convert inorganic or atmospheric nitrogen to an organic form. This “fixed” nitrogen is then utilized by the plants as “rent” in exchange for “room” and photosynthetically derived sugar provided to the bacteria to live and grow.
Seal, with her team, came across plants called Cattails that survive and thrive in highly nutrient-depleted soils, due to their symbiotic relationship with a pink fungus (Rhodotorula mucilaginosa) that provides nitrogen to these plants. The researchers isolated this pink fungus and set out to see if it can be colonized in rice, one of the most abundantly produced staple food crops and one that requires nitrogen for better yield.
The team successfully showed that the pink fungus can form a symbiotic relationship with the rice plant by forming filamentous structures in the plant body. Upon looking closely, the scientists also discovered that the fungus, in turn, harbours multiple nitrogen-fixing bacteria (e.g. Pseudomonas stutzeri) that are actually responsible for supplying the fixed nitrogen. This duo of pink fungus and nitrogen-fixing bacteria was able to promote the growth of rice plants, even in the absence of nitrogen supplements.
The researchers look forward to seeing this study applied to agriculture in the future. “This study has been primarily done inside the lab under controlled conditions. In the next stage, we would try to work in pots in a greenhouse with real soil,” explains Seal.
Discussing the prospective applications of this research, Alok Das, Senior Scientist, ICAR-Indian Institute of Pulses Research, Kanpur, says, “Reducing reliance on nitrogenous fertilizers has been a long-standing goal of researchers, principally to ameliorate their overuse and impact on the environment and subsequently on human health.” Das, who was not associated with this research, calls this study “landmark in terms of enhancing nitrogen use efficiency in rice, that can possibly be extended to other crops.”