Seed and foliar application of Trichoderma harzianum HE22 and Bacillus spp. prolong leaf rust latency, induce host defense responses, and improve wheat productivity

Wheat leaf rust, caused by Puccinia triticina, threatens the yield stability of susceptible cultivars, particularly in arid regions. This study aimed to assess the efficacy of selected microbial bioagents and their combinations in suppressing leaf rust and enhancing host defense responses and productivity under controlled and field conditions. Greenhouse experiments on wheat (Triticum aestivum L) cv. ‘Morocco’ evaluated Trichoderma harzianum HE22, Bacillus amyloliquefaciens, Bacillus subtilis, and their mixtures using seed soaking followed by foliar sprays applied at defined timings relative to pathogen inoculation; disease development was quantified via incubation/latent periods and pustule density, while induced resistance was assessed through total phenolics, salicylic acid, and activities of polyphenol oxidase (PPO), catalase (CAT), and peroxidase (POD). Field trials conducted across two consecutive seasons evaluated the same treatments for rust severity and area under the disease progress curve (AUDPC), as well as yield components and grain yield. All bioagent treatments significantly delayed symptom expression and sporulation, and reduced pustule density. Notably, HE22 applied 3 days post-inoculation extended the latent period to 13.67 days, compared to 10.00 days in the untreated control. Bioagent applications increased phenolic accumulation, salicylic acid content, and activities of PPO, CAT, and POD, consistent with the activation of systemic defense. Under field conditions, treatments especially T. harzianum HE22 consistently reduced disease severity and AUDPC, and improved 1000-kernel weight and grain yield. In contrast, mixtures were largely additive rather than superior to the best single agent. Overall, these results indicate that microbial bioagents can be integrated into sustainable management programs to mitigate leaf rust and stabilize wheat performance in arid environments.