Coating seeds with bacteria, silk, and sugar could allow plants to thrive in saline environments, according to a new study published on 25 November in Proceedings of the National Academy of Sciences (1). The new technique might provide an accessible and cheap way for farmers to make use of marginal lands that have been degraded by climate change.
Crops don’t grow well in highly saline environments, however, as the climate continues to change, the soil is getting saltier, and drought and extreme temperatures are more frequent. Moreover, poor water quality and use of agrochemicals degrade soil quality. In Morocco, for example, “land that was fertile 10 years ago is not fertile now due to the salinity of the soil”, says Prof Benedetto Marelli at Massachusetts Institute of Technology (MIT). So, Marelli and his team of researchers hope to use technology to mitigate this.
Nitrogen fertilizers are often added to topsoils to increase yields and ensure optimal growing conditions but have their own set of problems. Over-fertilisation can actually reduce crop yields, not to mention the serious environmental impacts — microbes in the soil convert nitrogen to nitrous oxide, a major greenhouse gas that contributes to climate change.
Rhizobacteria are a type of ‘nitrogen-fixing bacteria’ that can extract and convert nitrogen from the air into ammonia and other molecules required by plants through a process known as nitrogen fixation, thereby acting as a natural fertilizer. These ‘smart’ bio-fertilisers are being designed to boost germination while mitigating soil salinity and drought. However, bacteria can’t be kept alive for very long and are less affordable than fertilisers and therefore, out of reach for many small farmers.
To tackle these problems, Marelli and his colleagues at MIT developed a silk-based material that can be incorporated with so-called rhizobacteria and then used to coat seeds. The silk along with a type of sugar called trehalose preserve the bacteria. In fact, trehalose is naturally produced by many microbes to help them survive harsh conditions such as excess heat and drought. The researchers also selected a type of rhizobacteria known to tolerate heat and salty conditions.
The best part of their strategy is that silk and sugar are biodegradable and do not cause any additional damage to the environment like plastics and other synthetic materials would. And the coating can be simply sprayed onto seeds making the entire process quick, easy, and scalable.
Coating seeds increases germination and improves plant health
The researchers are currently focusing on agricultural lands in the Marrakesh-Safi region in Morocco, which is riddled with persistent drought stress and salinity. The first batch of seeds was tested in an experimental farm at the Mohammed VI Polytechnic University in Ben Guerir, Morocco.
Using the approach, the authors showed that chickpea and common bean seeds coated with a combination of rhizobacteria, silk, and sugar have increased germination rates and better overall plant health in highly saline soil compared to uncoated seeds.
More specifically, 88 per cent of coated seeds sprouted in non-salty soil compared with 62 per cent of non-coated seeds. In salty soil, 71 per cent of coated seeds sprouted versus 45 of non-coated seeds. Furthermore, the coated seeds resulted in longer stems and roots with more branches after just two weeks.
Expanding the technology
As the global population continues to grow, food production will need to increase by 70 per cent by 2050 to feed the estimated 10 billion mouths. However, many important food crops do not grow well in increasingly saline soil conditions, high temperatures, and drought stress. Next, the research team at MIT plan to look at plant growth in extreme temperatures and expand the work to other crops besides legumes.
(1) Zvinavashe, A.T. et al. A Bioinspired Approach to Engineer Seed Microenvironment to Boost Germination and Mitigate Soil Salinity. Proceedings of the National Academy of Sciences (2019). DOI: 10.1073/pnas.1915902116