Novel cyanobacteria-based seed coatings for enhancing germination, seedling vigour and iron nutrition in direct-seeded rice

The present study explores a novel seed-coating approach employing cyanobacterial formulations to enhance germination and seedling vigour in direct-seeded rice (DSR), as a sustainable alternative to traditional puddled transplanting. Beneficial cyanobacterial cultures and biofilms, namely Anabaena laxa (RPAN8), Anabaena torulosa-Trichoderma viride (An-Tr), and a consortium of Anabaena torulosa, Nostoc carneum, Nostoc piscinale and Anabaena doliolum (BF1-4); were used to coat seeds of Pusa Basmati 1509. The coatings combined carriers (vermiculite [V] and paddy straw compost: vermiculite [PV]), sticking agents (carboxymethyl cellulose [CMC] and gum arabic [GA]) and ferrous sulphate (FeSO4) as iron supplement, addressing the frequent iron deficiency in DSR systems. Initial screening of 81 coating combinations identified RPAN8 + PV + 1% CMC + 1% FeSO4 as the best formulation, exhibiting the highest percent germination and seedling-vigour indices. A subsequent plug-tray experiment compared selected coatings with hydropriming and microbial drenching. Treatments were assessed for germination, shoot and root growth, chlorophyll content, ferric chelate reductase (FCR) activity, dehydrogenase activity (DHA) and other biochemical parameters. CMC-coated seeds delivered superior biomass accumulation and seedling vigour (8–10% increment), whereas GA-based treatments enhanced root FCR and DHA activity (10–15% increment). Soil analyses revealed that GA + PV + FeSO4 achieved a five-fold increase in DHA compared to control. Principal-component analysis (PCA) demonstrated distinct clustering according to pigment content and microbial activity. Overall, optimized seed-coating formulations not only improved early plant performance and iron nutrition, but also outperformed hydropriming and drenching. These findings indicate that cyanobacterial seed coatings offer a promising, scalable and farmer-friendly strategy to boost rice productivity under DSR conditions.