Water deficit indicators and correlations with flowering of orange trees

Citrus flowering is influenced by stress conditions, primarily induced by low temperatures and/or water deficits. In the central-northern region of São Paulo, water stress is a critical factor in determining the timing of new flowering, which occurs promptly after the cessation of this stress. Farmers are motivated to enhance production by mitigating water stress through irrigation; however, they encounter challenges in accurately predicting the necessary level of stress and the optimal timing for irrigation to promote robust flowering. To identifythe physiological traits of the plants that can serve as reliable indicators ofwater stress as tools for studying inducing flowering in citrus, a trial was conducted inan orange grove of production age in Pitangueiras-SP. Five treatments were implemented, distinguished by the timing of water stress interruption (irrigation of 20 mm,biweekly): 1 - irrigation commencing in June; 2 - irrigation commencing in July; 3 - irrigation commencing in August; 4 - irrigation commencing in September; 5 - control treatment (no irrigation, with stress interruption only beginning in October with the return of regular rainfall), respectively to three to six months of deficit hydric. Monthly evaluations included measuring starch concentrations in leaves and branches, total chlorophyll content in leaves, electrolyte leakage from leaf tissue, NDVI (normalized difference vegetation index) indices, flower and fruit counts, and the quality of the harvested fruits. The results demonstrate that the NDVI index obtained from satellite imagery, electrolyte leakage from leaf tissue, starch concentration in branches, and the NDVI index from terrestrial cameras(ranked in descending order of importance) strongly correlate with the flowering of orange trees. These indicators provide vital tools for studying the effect of drought stress as a factor in inducing flowering in orange trees.