Journal of Agronomy and Field Innovations

Background: Onion (Allium cepa L.) is a globally important bulb vegetable whose productivity is increasingly constrained by water scarcity in semi-arid production zones. Shallow, sparsely branched root systems limit the crop's inherent capacity to withstand soil moisture deficits, creating an urgent need for sustainable, low-input strategies that strengthen root function without expanding irrigation demand.
Objective: This study evaluated the influence of plant growth-promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF), Trichoderma harzianum, and a combined microbial consortium on root architecture, physiological performance, and bulb yield of onion subjected to moderate and severe water deficit.
Methods: A field experiment was conducted using a Randomized Complete Block Design with eight treatments and three replications, combining three irrigation regimes (100%, 60% and 35% field capacity) with single and consortium microbial inoculations. Root morphological traits, relative water content, chlorophyll content, gas exchange parameters, proline accumulation, antioxidant enzyme activity, and yield and quality attributes were recorded and analyzed using ANOVA, Tukey's HSD, Pearson correlation, and Principal Component Analysis.
Results: Microbial inoculation, particularly the consortium treatment, significantly improved root length, volume, surface area and dry weight relative to non-inoculated controls under both deficit regimes (P ≤ 0.05). Inoculated plants maintained higher relative water content and photosynthetic rate, accumulated moderated proline levels, and produced 18-30% greater marketable bulb yield than corresponding controls, with root traits showing strong positive correlation with yield.
Conclusion: Microbial biostimulants, especially in consortium form, substantially enhance root development and physiological resilience of onion under water-limited conditions, offering a practical, environmentally sound component for climate-resilient onion production systems.