Introduction

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 (ETo) in interaction with microbial inoculants.

Method

Treatments were irrigation with 60, 80, 100 and 120% of the estimated ETo 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 applied. 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% ETo, although it was statistically equal (P≤0.05) to 100% ETo registering 42.86 and 40.58 cm respectively, 120% ETo 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 cm3 with respect to the control, and allowed to reduce the application of ETo by 20% to obtain the highest production of dry leaf and root biomass. The interaction R. intraradices + 80% ETo favored the assimilation of CO2 with 5.41 μmol m-2 s-1, thus providing better conditions for transpiration and efficient water use (1.87 μmol CO2 mmol-1 H20).

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 / MSR ratio and yield. Finally, the interaction of both factors was only significant in the parameters of dry biomass production and gas exchange.