Growth and ornamental quality of potted Bougainvillea genotypes grown in two shapes under deficit irrigation

Deficit irrigation (DI), that involves the application of water at a rate and volume lower than the evapotranspiration rate throughout the whole growth period, may be used in potted ornamental plants to improve plant quality. The interest in DI has primarily centred on water savings and/or to control excessive vegetative growth mainly in fruit trees and vegetables, whereas its application to ornamental crops has received limited interest so far. Bougainvillea is a genus of flowering plants widely used in the arid landscapes due to its high adaptability in different agro-climatic regions. Despite the importance of the Bougainvillea in floriculture production, no published data is available on the effects of different levels of DI on agronomical parameters and ornamental quality of Bougainvillea. The aim of this study was to determine the effects of three irrigations treatments on the growth responses and ornamental value of Bougainvillea genotypes, trained to two canopy shapes. Plant growth, ornamental quality, mineral composition and water use efficiency, were measured during the growing cycle. The experiment was conducted glass-zinc-coated steel greenhouse situated at the Experimental Station of the University of Naples Federico II, South Italy. Rooted cuttings of three flowering potted Bougainvillea genotypes, (B. glabra var Sanderiana, B. x buttiana ‘Rosenka’, B. 'Aurantiaca') were transplanted on March 1st, into pots containing peat moss and placed on troughs, with a plant density of 6 plants·m-2. Bougainvillea plants were grown in two canopy shapes: globe and pyramid. Treatments, arranged in a randomized complete block design with three replicates, were defined by a factorial combination of three irrigation levels based on the daily water use (100%-C, 50%-MDI, or 25%-SDI), three Bougainvillea genotypes, and two canopy shapes. The shoot, total dry biomass, leaf number, leaf area, and macronutrient concentration decreased in response to an increase in water stress, with the lowest values recorded in the SDI treatment. The percentage of total dry biomass reduction caused by irrigation level, was lower in B. x buttiana ‘Rosenka’, compared to B. glabra var Sanderiana and B. 'Aurantiaca'. At the same date, the flower index increased in response to an increase in water stress, with the highest values recorded under both MDI and SDI for B. x buttiana ‘Rosenka’. The MDI treatment can be used successfully in Bougainvillea to reduce water consumption while improving the overall quality and WUE, whereas the genotypes B. glabra var Sanderiana and B. x buttiana ‘Rosenka’ could be considered suitable for pot plant production. These results can play an important role for the ornamental industry, which is very interested in selecting tolerant genotypes and suitable shapes under water stress conditions, and to evaluate the DI as a useful technique to save water without affecting the economic value of the plant