Physiological defensive modes to biologically induce drought tolerance in broccoli via inoculation with mycorrhiza and Trichoderma

Abstract

Purpose: Recently, conserving irrigation water via application of deficit irrigation is a main priority, particularly in aridity and semi- aridity conditions. However, water deficiency is one of the major issues that hinder crop production worldwide. Also, knowledge regarding the physiological efficiency of microbial inoculation (MI) to shrink drought impacts in broccoli is unclear. We hypothesized that AMF and TRI fungi may have different mechanisms to modulate the physiological state and growth of broccoli to be more tolerant to drought stress. Methods: A field experiment in two seasons of 2023-24 and 2024-25 was conducted to assess the influence of MI on drought tolerance in broccoli. A mycorrhiza inoculum (AMF) and Trichoderma (TRI) inoculum were applied under 100, 80, 60 and 40% of irrigation requirements, IR (referred to as IR100, IR80, IR60 and IR40, respectively). Firstly, the MI was applied in the nursery after sowing the seeds in the seed trays, further, MI was applied two times, 28 and 38 days after transplanting (DAT) with the drip irrigation system, while the irrigation regimes started on 27 DAT. The treatments were designed in a strip-plot system in a complete randomized block with three replicates (trial unit size was 12 m²). At 70 DAT, soil plant analysis development (SPAD), membrane stability index (MSI), relative water content (RWC), proline content, enzymatic and non-enzymatic antioxidants and total antioxidant activity of broccoli leaves were assessed, while at 85 DAT the fresh and dry weight of shoot and root, leaf area and head yield were estimated. Results: Findings clarified that application of AMF and TRI inoculations under different levels of drought improved significantly (p < 0.05) SPAD, MSI and RWC compared to the corresponding control treatments, except AMF with IR60 for SPAD and TRI with IR60 for SPAD and MSI and with IR40 for SPAD. Under IR60 regime, AMF achieved the maximum improvements (p < 0.05) in peroxidase, polyphenol oxidase and superoxide dismutase, significantly equaling (p > 0.05) TRI for peroxidase. AMF×IR60 was the effective interaction for achieving the maximal values of total phenolic, total flavonoids and total antioxidant activity in broccoli, equaling (p > 0.05) TRI×IR60 combination in total phenolic. Compared to the counterpart control (CK) treatments the increases in proline content due to AMF or TRI applications amounted to 26.4 and 30.0% with IR80, 25.0 and 15.6% with IR60 and 36.6 and 32.5% with IR40, respectively. It is worth to observe that IR80×AMF combination achieved shoot dry weight and head yield values similar (p > 0.05) to IR100×AMF combination. Conclusion: Briefly, it can be concluded that microbial inoculations, specifically AMF, can relieve the injuries of drought. Practically, broccoli growers can save irrigation water by 20% with inoculating plants by mycorrhiza to maintain crop productivity and quality under water deficiency circumstances.