Bacteria help rice grow more roots to fight drought, research says

Results of a study reveal that a certain bacteria can induce larger and more extensive root system when applied to planted rice, thereby improving drought tolerance.

The study was conducted by a group of scientists from the Philippine Rice Research Institute (PhilRice), along with students from Muñoz National High School in Science City of Muñoz, Nueva Ecija.

Led by Dr.Roel R. Suralta of PhilRice, the researchers reported that rice applied with a dose of the bacteria Streptomyces mutabilis showed improved drought tolerance because of its larger roots and more extensive root system.

The study aims to improve the root system of rice grown in uplands where water is scarce.

“Upland areas are 100% dependent on rainfall to support rice production,” said Suralta. “Due to the uncertainty of rainfall brought by climate change, these areas become more and more prone to the occurrence of drought stress,” he explained, adding that 10 to 15 percent of all rice fields in the country are considered as upland. (upland, because it is used as adjective)

How were the experiments done?

In the study, the researchers used a method called inoculation which is likened to vaccination. A particular microorganism called Streptomyces mutabilis isolated from Binangonan, Rizal was used for inoculation. Identified as a plant growth-promoting bacteria or PGPB, Streptomyces mutabilis supply the host plant with nutrients and enzymes.

To prepare the inoculation, Streptomyces mutabilis was grown in a broth filled with nutrients. The broth was then applied to a sterilized soil sample and later on, to the soil where the rice seedlings will be sown.

The study had two experiments. In the first one, the researchers tested if the seeds of the rice variety NSIC Rc192 (Sahod Ulan 1) would have enhanced shoot (collective term of the plants’ leaves and stems) and roots due to the inoculation of rice with Streptomyces mutabilis.

In the second experiment, the researchers inoculated rice also with Streptomyces mutabilis at different times (see photo) in a setup mimicking a drought stress. The Central Experiment Station of PhilRice in the Science City of Muñoz, Nueva Ecija housed these experiments.

Results of the first experiment showed that rice seeds treated with Streptomyces mutabilis expressed longer shoot and roots three days after germination (the process by which an organism grows from a seed) as compared with untreated seeds. Inoculated rice also had more and longer root hairs, thus its roots can absorb more water and nutrients.

Meanwhile, inoculated rice in the second experiment also have grown longer roots even in a drought-like setup and contributed to the increase in soil water uptake and maintenance in greater shoot growth.

The researchers also weighed the shoot parts of rice that have been oven dried (also known as dry mass) to measure the plant’s development. The researchers figured out a unique “trade-off” between inoculation and dry mass production: the rice that had more inoculation produced less dry mass. Why? Repeated inoculation might have increased the population of bacteria, thus creating an unhealthy competition between the roots and bacteria for soil nutrients.

In the paper, the researchers clarified that other factors stressful for plants like extreme temperatures, pests and pathogens, and nutrient deficiencies were not tested.

The full article of the study “An Enhanced Root System Developmental Responses to Drought by Inoculation of Rhizobacteria (Streptomyces mutabilis) Contributed to the Improvement of Growth in Rice” can be downloaded for free in the Philippine Journal of Science Volume 147 No. 1 at philjournalsci.dost.gov.ph. The photos were taken from the published paper.

uninoculated_vs_inoculated

Uninoculated versus inoculated. Top: Seedlings treated with Streptomyces mutabilis have longer leaves and roots compared with untreated ones. Bottom: Viewed through a microscope with 400x magnification, treated seedlings have more hairy roots, making them more effective in getting nutrients and water from soil. The researchers dyed the roots for easy viewing. (Please check proper use of “compared to” and “compared with”)

uninoculated_vs_inoculated

Inoculation at different times. Rice seedlings that received inoculation have more complex root system compared with the uninoculated ones. The researchers say that the seedling on the third photo has the most number of root hairs. DAS stands for day/s after sowing. (correct use of “compared with”, but don’t use “as” anymore)

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