Sustainable management of Alternaria leaf blight in isabgol (Plantago ovata) using chitosan, multi-walled carbon nanotubes, and salicylic acid

Introduction Alternaria leaf blight, caused by Alternaria alternata (Fr.) Keissler, is one of the most destructive diseases of isabgol ( Plantago ovata Forsk). Conventional fungicide-based control raises environmental concerns and threatens long-term sustainability. Therefore, eco-friendly plant defense activators offer potential alternatives for sustainable disease management and food security. Methods This study assessed the efficacy of chitosan, multi-walled carbon nanotubes (MWCNTs), and salicylic acid (SA) under both laboratory and field conditions. In vitro assays were carried out to evaluate mycelial inhibition, while field trials were performed during two consecutive Rabi seasons (2022–2023 and 2023–2024) under a randomized block design (RBD) at Swami Keshwanand Rajasthan Agricultural University, Bikaner, India. Treatments involved seed priming and foliar application at various concentrations. Results In vitro , salicylic acid (200 ppm) and chitosan (150 ppm) exhibited the highest pathogen inhibition (67.14 and 62.60%, respectively), followed by MWCNTs (45.45% at 150 ppm). Field evaluations revealed that chitosan (100 ppm, seed treatment + foliar spray) significantly reduced disease severity (51.30%) and improved yield (805.29 kg/ha). Salicylic acid at 200 ppm provided the greatest overall benefit, with 55.60% disease control and the highest yield (837.06 kg/ha). The least effective treatment reduced disease by only 10.87% with a yield of 665.69 kg/ha. Conclusion This study supports sustainable agriculture by integrating eco-friendly defense activators that reduce chemical fungicide dependence. Considering the Asia-Pacific context, such low-input, resource-efficient approaches can enhance smallholder resilience in arid and semi-arid ecosystems.