Productivity of Stevia rebaudiana Bertoni with different irrigation slides and microbial inoculants

Introduction: The leaves are the most important organ in the plant of Stevia rebaudiana Bertoni, because in them is the greater amount of sweetener. Leaf emission is determined by adequate root growth and the amount of water available in the soil. The objective of the present study was to evaluate the respond of S. rebaudiana Bert plants to four irrigation sheets calculated from reference evapotranspiration (ET o ) in interaction with microbial inoculants. Method: The treatments consisted of irrigate with 60, 80, 100 and 120% of the estimated ET o with an "A" type evaporimeter tank in previously inoculated plants. A mixture of Bacillus spp. and Azospirillum brasilense , Rhizophagus intraradices and a control (uninoculated). A randomized complete block design with bi-factorial arrangement and four replicates was used. Growth, production and distribution parameters of dry biomass, gas exchange and water efficiency were evaluated. Results: Statistical difference (P≤0.05) was found by separate factors. The best height was obtained with 120% ET o , although it was statistically equal (P≤0.05) to 100% ET o registering 42.86 and 40.58 cm respectively, 120% ET o was recorded greater leaf area. Treatment with Rhizophagus intraradices showed significant differences (P≤0.05) in the root length against the control, but not against the mixture of rhizobacteria. In the same way R. intraradices improved the root volume by registering 2.49 cm 3 with respect to the control, and allowed to reduce the application of ET o by 20% to obtain the highest production of dry leaf and root biomass. The interaction R. intraradices + 80% ET o favored the assimilation of CO 2 with 5.41 μmol m -2 s -1 , thus providing better conditions for transpiration and efficient water use (1.87 μmol CO 2 mmol -1 H 2 0). Conclusion: The irrigation factor showed effect on leaf height, leaf area, stem diameter and dry leaf yield, while inoculating factor only affected root length, root volume, MSV / MRS ratio and yield. Finally, the interaction of the two factors was only significant in the parameters of dry biomass production and gas exchange.