Soil plays big role in microbiome of plants: UoH study

Red gram (pigeon pea, ‘arhar’ in Hindi, ‘kandi’ in Telugu) is an important staple crop that significantly contributes to the protein intake in vegetarian diets across many countries, including India.

It is often referred to as the “poor man’s protein. Red gram thrives as a rainfed crop in the semi-arid regions of the world. Roots of red gram from small and variously shaped nodules engage in a symbiotic association with nitrogen-fixing bacteria, especially with Bradyrhizobium, one of the commonly known rhizobia. 

Red gram and other legumes as hosts benefit from the symbiotic relationship with the rhizobia, because the rhizobia converts atmospheric nitrogen - comprising over 75% of the air - into a form plants can use, thus reducing the need for external nitrogen fertilisers for small and marginal farmers. 

The nodules of red gram are not just filled with rhizobia alone, but several other microbes which are also present within and around them. This natural structure can significantly impact their efficiency in fixing atmospheric nitrogen in the natural process. 

New Research by UoH
Prof. Appa Rao Podile and his team at the University of Hyderabad (UoH) conducted a comprehensive metagenome analysis to explore the factors influencing the microbiome diversity within red gram nodules. 

The former Vice Chancellor and his team examined different red gram genotypes like Asha, Durga, and Mannem Konda Kandi grown in different types of soils (Alfisol, Vertisol, and Inceptisol), as well as a wild relative of red gram in its native soil.

Supported by the Science and Engineering Research Board (SERB), now known as Anusnadhan National Research Foundation (ANRF), under the Department of Science and Technology (DST), Govt of India, Prof. Appa Rao with his Ph.D. students Dr. Anirban Basu, Dr. Chalasani Danteswari and Dr. PVSRN Sarma, at the Department of Plant Sciences, University of Hyderabad has taken up this systematic study on the microbiome of red gram nodule.

The Salient Findings 
The presence of non-rhizobial bacterial endophytes in the red gram nodules was evident all through. The position of the nodule on the root, the type of soil in which the red gram is grown, the variety (genotype of the red gram), and other environmental factors that contribute to the composition of the nodule microbiome were revealed through this study.   

While the diversity of microbiome in the nodule is less compared to bulk soil, it was more specialised, indicating  the role of host selection, the researchers found.

Another significant finding was that the microbiome of the wild relative of red gram was dominated by Bradyrhizobium while the cultivated varieties like Asha, Durga, and Mannem Konda Kandi had exhibited diverse bacterial communities. In the process of domestication, the native symbiosis appears to have been compromised. 

The study also highlighted that soil properties played a greater role than the host plant genetics in shaping the nodule microbiome, indicating the importance of soil in deciding the microbiome of plants. 

These findings were published recently in the journal “Environmental Microbiome”, published by Springer Nature, according to the UoH.