Effect of biochar and seed priming with Trichoderma spp. on the occurrence of Alternaria blight in rapeseed mustard (Brassica juncea L.)

Brassica juncea is an important oilseed crop of the family Brassicaceae. In India, its productivity is limited by various plant diseases including Alternaria blight. To evaluate the effect of biochar application and seed priming with Trichoderma spp. (T. harzianum and T. viride) on the growth, yield, and disease parameters of rapeseed mustard (B. juncea var. PBR 91), the present study was conducted during the rabi season of 2024-25. The field experiment was laid out in a randomized block design (RBD) with ten different treatments of biochar, Trichoderma spp., and the combinations thereof. Out of different combinations tested, the treatment T₄ i.e., RDF (recommended dose of fertilizers) + seed priming (SP) with T. viride 50% + T. harzianum 50%, significantly reduced the number of days to 50% germination (4.50 DAS), and increased plant height (208.93 cm at 90 DAS), number of leaves (58.51), number of branches (28.33), promoted early flowering (61.50 DAS), and improved plant and shoot fresh weights (91.20 g at 90 DAS and 44.43 g, respectively). It was also useful in increasing the number of siliquae (235.50), seeds per siliqua (15.80), and seed yield per plot (668.16 g). The treatment T₄ also delayed the initial appearance of Alternaria blight (83 DAS) and showed the lowest disease incidence (48.29%), severity (21.09%), and AUDPC value (447.51). In contrast, the control treatment, T₁ (RDF only) recorded the poorest performance in all parameters including maximum disease incidence (54.54%), severity (29.12%), and AUDPC value (716.40). Interestingly, biochar treatments (alone or in combination with Trichoderma spp.) showed some improvement in all the parameters than the control, but were less effective than seed priming with the fungal biocontrol agent, Trichoderma spp. (especially, the treatment T₄). Therefore, it may be concluded that seed priming with a balanced mixture of T. harzianum and T. viride (both at 50% dose) is quite effective in enhancing mustard growth, yield, and in reducing Alternaria blight incidence under field conditions.