Engineering crop seeds to resist drought

To counteract the impact of drought on crop seeds,  scientists at the Massachusetts Institute of Technology have developed an innovative two-layer coating that will provide seeds with both water and nutrients during the critical germination stage. MIT.edu/Felice Frankel photo

With persistent global warming and heatwaves threatening to be more intense and more frequent, many arid regions and areas experiencing significantly less rainfall will be under increasing agricultural stress. The shifting balance between water supply and demand will be one of the biggest challenges facing farmers in the years to come.

To counteract the impact of drought on crop seeds, scientists at the Massachusetts Institute of Technology have developed an innovative two-layer coating that will provide seeds with both water and nutrients during the critical germination stage. The coating is the result of years of research and trials by Benedetto Marelli, MIT professor of civil and environmental engineering, MIT doctoral student Augustine Zvinavashe, and the research team at both MIT and the King Mohammed V1 Polytechnic University, Ben Guerir near Marrakech, Morocco.

“The gel-like coating is made up by a cocktail of polysaccharides, mainly pectin and methylcellulose,” said Marelli. “The structural part of the coating is mostly pectin while cellulose is washed out as it is a filler used to increase the water-holding capacity of the gel. The polysaccharides used may be extracted from food waste such as orange peel. Thus, we can think of upscaling the byproducts of the AgriFood industry to promote a circularity of the resources used.”

Marelli stated in the report that plant seeds produce a mucilage-based hydrogel, a thick, gluey substance, that creates a germination-promoting microenvironment by retaining water, regulating the entry of nutrients and facilitating interactions with beneficial microorganisms. Plants such as chia, basil, cacti, other succulents, and flax seeds are rich sources of mucilage. Taking a cue from this natural coating, the researchers developed the two-layered biopolymer-based coating to promote germination and increase water-stress tolerance for seeds sown in semi-arid, sandy soils.

“The inner coating layer is dip-coated into the seed,” he said. “The nutrients are encapsulated in the material. Silk is a great material for encapsulation, preservation, and release of active components such as nutrients and microbes. The two coats are applied separately. You can spray them on or dip coat them onto the seed.”

The team used a common bean (Phaseolus vulgaris) cultured under water-stress conditions at the experimental farm in Ben Guerir. Marelli said that the inner silk/trehalose layer containing rhizobacteria is much thinner than the pectin methylcellulose outer layer that re-swells upon sowing and acts like a water jacket. The two coatings adhere to each other through the formation of physical bonds (electrostatic interactions and hydrogen bonds). The seed coating effectively delivered the rhizobacteria to form root nodules which resulted in plants with better health, and which mitigated water stress in drought-prone marginal lands.

“Our idea was to provide multiple functions to the seed coating,” he said. “Not only targeting this water jacket but also targeting the rhizobacteria. This is the real added value to our seed coating because these are self-replicating microorganisms that can fix nitrogen for plants so that they can decrease the use of nitrogen-based fertilizers and enrich the soil.”

The materials needed for the coatings are readily available and often used in the food industry. They are fully biodegradable and since some of the compounds can be derived from food waste they provide a closed-loop recycling system.

If the coatings prove their value through further tests, they are simple enough for application at the local level, even in remote locations in the developing world.

“That is one of the things we were thinking about while we were designing this,” said Zvinavashe. “The first layer you could dip coat and then the second layer you can spray it on. These are very simple processes that farmers can do on their own.”

However, Zvinavashe thought it would be more economical to do the coatings at a central location in facilities that can more easily preserve and stabilize the nitrogen-fixing bacteria.

“In the design process, we talked with stakeholders on the field and targeted an innovation that could retrofit existing tools commonly used by growers and farmers around the world, or by the seed industry,” said Marelli.

The research team has been conducting field studies for the past two years. The pandemic halted the research for the 2020 growing season so the data is now being collected and analyzed. He said that the preliminary studies already showed enhanced resistance to drought stress in semi-arid soils. Trials for the drought tolerance from seedling to harvest are still ongoing with start-up occurring soon. However, soil salinity tests have already been conducted. The first stages have been to show efficacy in the lab, then in the greenhouse, then field studies. So far, he indicated, the results have been interesting.

“This model can be applied to all seeds with some optimization for each seed type,” he said. “We started with green bean as our model. However, it is easily transferable to soybean which is massively produced in the U.S. and important for diets (oil, soy milk, tofu, soy protein, soy meal for livestock). Our goal is to be able to be on every seed for the most important crops for humans such as corn, wheat, soybean and legumes that contribute to provide non-animal proteins.”

Marelli believes that to make the AgriFood system more sustainable and resilient, we need to develop innovative, specific solutions that target the challenges that climate change will bring.

“The effects of extreme weather and erratic weather patterns are becoming more and more visible both in North America and the Mediterranean basin. Having these challenges in mind, we are developing solutions that can be designed around specific soils and predicted weather patterns to mitigate the detrimental effects of climate change on soil and the increase in abiotic stresses. Thus the choice for tailoring seed coatings for specific locations to boost productivity.”

He emphasized that the germination phase is critical in early plant establishment which is why there is a need to target minimization of water stress to promote plant health at an early stage. The technology is expected to not only increase germination rate and plant vigour but also most likely fruit quality thus boosting yields and, therefore, profitability for farmers.

The expectation is that, within a few years and the right investment strategy, a product should be on the market.

The research was published in Nature Food.


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