Silicon and bioagents pretreatments synergistically improve upland rice performance during water stress

Rice (Oryza sativa L.) is one of the most important food crops worldwide. Upland rice growing areas are susceptible to adverse conditions and drought represents the main limiting factor for its production and yield stability. Soil management strategies (e.g., chemical and biological treatments) are often implemented to mitigate drought and improve crop production. However, morpho-physiological responses of upland rice to drought under such management strategies remains poorly understood. Here, we studied the effect of silicon and bioagents pretreatments under water stress on an upland rice landrace, Samambaia Branco. Our results unraveled that these pretreatments improved robustness of the root system in water stressed plants with increase in 40.9% of surface area, 11.5% on diameter, 53.8% on volume and 30.8% of length density when measured at 45 cm soil depth. Furthermore, these treatments increased number of thick roots by more than 14.0 and 45.0% at 25 and 45 cm soil depths, respectively; and fine root by more than 25.0% at 45 cm soil depth. Consequently, pretreated water stressed plants exhibited greater yield stability (reduction of 14.6% in grain yield compared to pretreated well-watered plants), root/shoot ratio (26.8%), photosynthesis (50.0%), stomatal conductance (14.4%), leaf water potential (61.0%) and water use efficiency (49.1%) than untreated water stressed plants. Thus, we conclude that silicon and bioagent pretreatments significantly improve root and shoot performance under water stress. Our results provide a first step towards understanding the relevance of these pretreatments in upland rice for improving adaptive root system as a response to suboptimal environmental conditions