Deciphering physiological mechanisms of biopolymeric seed coatings in oilseed crops

Oilseed crops experience substantial yield losses due to rapid seed deterioration, inconsistent moisture availability, early pathogen pressure, productivity and storability, particularly in smallholder systems. To meet these constraints, an eco-friendly, biopolymer-based double-layer seed coating containing multiple crop inputs, (fungicide, Trichoderma harzianum (Th4d), and a crop-specific biofertilizer (Azotobacter, Bradyrhizobium, and Rhizobium) for sesame, soybean and groundnut, respectively was developed. The layer-by-layer configuration ensured spatial separation and sequential release of chemical and biological inputs, enhancing compatibility, persistence, and functional delivery. Double-Layer Coating (DL-R) treatment was validated under laboratory, greenhouse, and field conditions in groundnut, while its efficacy under laboratory and greenhouse assays was confirmed in sesame and soybean. DL-R consistently retained the highest germination after storage (78.8-86.7%), with only 5-8% decline compared with 56-58% and > 12-23% decline in untreated seeds. Microbial viability remained superior with DL-R (2.86-2.94 Log CFU g⁻¹ for T. harzianum; 4.69-4.92 Log CFU g⁻¹ for biofertilizers), 0.3-0.5 Log units higher than control. Laboratory and greenhouse assays showed 60-75% lower seedling mortality than untreated seeds across all crops. In groundnut field trials, DL-R improved emergence (↑20-27%), reduced stem rot (↓80%), lowered pest load (↓50-70%), and achieved the highest yield (21.1 q ha⁻¹ vs. 12.9 q ha⁻¹), with the maximum B: C ratio (1:2.41). This study demonstrates a scalable double-layer coating platform that enhances seed protection, microbial symbiosis, and yield, providing a low-chemical pathway for resilient oilseed production.