The Irrigation Deficit and Its Effects on Physiology and Phenology of ‘Navelate’ Oranges Trees in Brazil

Aims: The aim of this research was to study physiological responses and changes on phenology of ‘Navelate’ orange trees submitted to different water stress intensities in a greenhouse.

Study Design: The experimental design was completely randomized, with three replications in each experimental unit. Values of each parameter were submitted to variance analysis, compared by Tukey’s test at 5% significance and showed as averages.

Place and Duration of Study: The experiment was carried out in a greenhouse (latitude 31°52'00 "S, longitude 52°21'24" W, 13 m above sea level), during 2014 and 2015.

Methodology: Stressed conditions were based on 50% and 25% of the field capacity. Gas exchange [photosynthesis (A), transpiration (E), stomatal conductance (gs), water use efficiency (WUE)] were analyzed using an infrared gas analyzer, model Li-6400 (Portable Photosynthesis System LICOR, Nebraska, USA), in addition to growth parameters.

Results: Reductions on photosynthetic rate were observed (10.74% for T-50, and 20.66% for T-25, both compared to Control), indicating that CO2 assimilation rate was affected by water stress conditions. Water stress affected all gas exchange parameters of the exposed orange trees, limiting growth in diameter and height. Fruit yield decreased with the amount of water (100%> 50%> 25%).

Conclusion: Navelate orange plants exposed to water deficit were tolerant in the initial phase of the treatments and during the vegetative phase, being more sensitive in the reproductive period. Plants submitted to stress with 25% of field capacity, presented limitations compared to control plants under full water availability, such as differences in height, diameter and fruit production. Water stress, at any level, reduced plant growth and fruit production. Therefore, due to variations in phenological parameters among the treatments, further studies should be performed on these variables to search for water deficit tolerant varieties and quality fruits production under these conditions.