Bioformulation of Silk-Based Coating to Preserve and Deliver Rhizobium tropici to Phaseolus vulgaris Under Saline Environments

Abstract

Seed priming has been for a long time an efficient application method of biofertilizers and biocontrol agents. Due to the quick degradation of the priming agents, this technique has been limited to specific immediate uses. With the increase of awareness of the importance of sustainable use of biofertilizers, seed coating has presented a competitive advantage regarding its ability to adhere easily to the seed, preserve the inoculant, and decompose in the soil. This study compared primed Phaseolus vulgaris seeds with Rhizobium tropici and trehalose with coated seeds using a silk solution mixed with R. tropici and trehalose. We represented the effect of priming and seed coating on seed germination and the development of seedlings by evaluating physiological and morphological parameters under different salinity levels (0, 20, 50, and 75 mM). Results showed that germination and morphological parameters have been significantly enhanced by applying R. tropici and trehalose. Seedlings of coated seeds show higher root density than the freshly primed seeds and the control. The physiological response has been evaluated through the stomatal conductance, the chlorophyll content, and the total phenolic compounds. The stability of these physiological traits indicated the role of trehalose in the protection of the photosystems of the plant under low and medium salinity levels. R. tropici and trehalose helped the plant mitigate the negative impact of salt stress on all traits. These findings represent an essential contribution to our understanding of stress responses in coated and primed seeds. This knowledge is essential to the design of coating materials optimized for stressed environments. However, further progress in this area of research must anticipate the development of coatings adapted to different stresses using micro and macro elements, bacteria, and fungi with a significant focus on biopolymers for sustainable agriculture and soil microbiome preservation.

Biomaterials Technology for AgroFood Resilience

“…More recently, the use of silk fibroin-a structural protein extracted from Bombyx mori cocoons in the design of functional seed coatings has opened up new possibilities for sustainable agriculture on marginal lands. [43,82,83] A recent example showcases the use of silk fibroin in combination with trehalose as seed coatings that encapsulate, preserve, and deliver Rhizobium tropici to Phaseolus vulgaris seeds upon sowing, [82] which effectively boosted germination and seedling growth in saline soils (Figure 2a-d). Such biomaterial formulation for seed coatings synergistically employs the film-forming, payload encapsulation, preservation, and tunable biodegradation capabilities of silk fibroin and the ability of trehalose to support survival of rhizobacteria during desiccation and resuscitation.…”

“…A follow‐up study compared the performance of Phaseolus vulgaris seeds coated by a thin film of silk fibroin, trehalose, and Rhizobium tropici to seeds primed with Rhizobium tropici and trehalose, respectively. [ 43 ] The results showed that coated seeds exhibited the highest germination rate in soils of increasing salinity and more articulated roots were developed from coated seeds compared to primed seeds and untreated controls.…”

“…[ 42 ] Common bean ( Phaseolus vulgaris ) seeds primed with Rhizobium tropici showed higher germination rate, enhanced seedling development, more articulated roots and better adapted physiological activities in saline environments when compared to untreated controls. [ 43 ] For non‐legume crops, free‐living nitrogen fixers such as Azospirillum and Azotobacter are commonly used in seed priming. [ 18 ] Phosphorus‐ and potassium‐solubilizing microorganisms function mainly by secreting metabolites (mostly organic acids) that can transform insoluble P‐ and K‐bearing minerals into solubilized and accessible forms for plant uptake, through a series of chelation, exchange reaction, acidification, and dissolution processes.…”

“…More recently, the use of silk fibroin—a structural protein extracted from Bombyx mori cocoons in the design of functional seed coatings has opened up new possibilities for sustainable agriculture on marginal lands. [ 43,82,83 ]…”

Biochar Coating Is a Sustainable and Economical Approach to Promote Seed Coating Technology, Seed Germination, Plant Performance, and Soil Health

“…Seed priming resulted in synchronized emergence, and uniform stand establishment due to a decline in the lag time to imbibition and a better repair of metabolic segments and osmotic adjustment [ 8 , 9 ]. Nevertheless, seed priming is facing many challenges, such as product conservation, viability losses during storage, and difficulties in upscaling management [ 2 , 10 ]. Moreover, this makes the process time-consuming and cumbersome when priming large quantities of seeds that require subsequent drying.…”