Seeds in Silk Coats

Silk mixed with bacteria and nutrients make a coating for seeds that can help them grow in salty soil.

Benedetto Marelli

As climate patterns change, growing enough food for an increasing global population will become evermore challenging. There is a need to develop technologies that enhance agricultural output without causing negative impacts on soil and surrounding ecosystems. Now, a group of scientists have created an environmentally friendly biomaterial that helps seeds grow in degraded soils.

Benedetto Marelli and his team at the Massachusetts Institute of Technology developed a seed coating made from silk fibroin, a material extracted from silkworm (Bombyx mori) cocoons, and trehalose, a sugar. The resulting silk-trehalose mixture has unique properties that can preserve dormant nitrogen-fixing rhizobacteria within it. Once seeds with the silk-trehalose coating are planted, the bacteria resuscitate and provide the seed with a natural source of fertilizer.

In laboratory tests, the researchers planted coated and non-coated common bean seeds (Phaseolus vulgaris) in two soil types: one with a high salinity that would normally inhibit growth, and one with low salinity. Over a two-week period, coated seeds showed 30 and 40 percent increases in germination in the low- and high-salinity soils, respectively, when compared to non-coated seeds. The coated seeds also resulted in plants that grew faster, with longer stems and better root development.

In contrast to the process of creating commercial nitrogen fertilizers, which, according to Marelli, “is responsible for 1.4 percent of carbon emissions going into the atmosphere,” creating the silk-trehalose coating produces few greenhouse gases. Additionally, Marelli noted that the targeted deployment of fertilizer to individual seeds “may result in decreased use of nitrogen-based fertilizers, which are known to degrade soil if applied in large, non-specific quantities.”

The seed coating can be cheaply applied by farmers using existing technology, and the team is now testing it in saline soils in Morocco. Although more studies need to be done, Marelli said that early results are positive. The team is also investigating how the composition of the seed coating can be changed and adapted to other plant species, growing locations, and soil conditions, such as those found in areas experiencing drought. (Proceedings of the National Academy of Sciences)