Chitosan Nanoparticles as Smart Carriers of Hexaconazole for managing rice blast incited by Pyricularia oryzae Cavara

Rice blast, caused by the fungal pathogen Pyricularia oryzae , remains a major constraint on global rice production, significantly affecting yield and quality. In our previous study in evaluating the efficacy of various fungicides on P. oryzae ; hexaconazole emerged as the most potent antifungal agent. Hence, in the current study, hexaconazole was further encapsulated in the nano particles of a bio-macromolecule, chitosan (HECNPs) and characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), zeta potential and gas chromatography-mass spectrometry (GC-MS) analysis. These assessments confirmed the successful synthesis of nano-formulated hexaconazole, exhibiting superior stability and controlled release properties when compared to commercial hexaconazole. The half maximal effective concentration (EC ₅₀ ) of hexaconazole and HECNPs were found to be 800 ppm and 200 ppm, respectively. The dissipation of hexaconazole in paddy leaves sprayed with HECNPs were quantified at 0, 5, 10 and 15 days and observed the improved dissipation dynamics of HECNPs over commercial hexaconazole. Field experiments and Uniform Blast Nursery (UBN) trials validated the superior performance of HECNPs in disease suppression and yield improvement. The application of HECNPs at a rate of 12.5 g active ingredient (a.i.) per hectare with two foliar sprays achieved the lowest disease incidence of 25.1% and highest yield of 3166.6 kg ha ^-1 leading to the highest net returns per rupee invested (NRRI) of 3.66 in season 1 and 3.53 in season 2. These findings confirm that nano-encapsulation technology using HECNP enhances disease management besides aiding economic feasibility of rice blast management strategies.