Fluorescence phenotyping in blueberry breeding for genotype selection under drought conditions, with or without heat stress

Lack of water and increase in ambient temperature, caused by climate change, are already affecting agriculture worldwide. These factors will affect the physiology and development of plants in general, including blueberry plants (Vaccinium spp.). With this in mind, six cultivars of highbush blueberry (Vaccinium corymbosum L.) ('Star', 'Bluecrisp', 'Jewel', 'Bluegold', 'Elliott' and 'Liberty') and two rabbiteye cvs. (Vaccinium ashei R.) ('Bonita' and 'Powderblue') were subjected to two water treatments: continuous irrigation (Full irrigation-FI); and with a water deficit (only one third of the volume of water, water deficit-WD). Both treatments were applied in two greenhouses one of which represented ambient conditions (At) and the other simulated heat stress conditions (At + 10 °C). Measurements were made of chlorophyll fluorescence, stem water potential (Ψs), chlorophyll content, leaf temperature and SPAD. In At conditions, cultivars showed differences in most parameters of chlorophyll fluorescence, but only the quantum yield of energy conversion of non-photochemical quenching (Y(NPQ)) and Ψs were significant, along with interactions between cultivars and irrigation treatments. In addition, cultivars differed in the maximum rate of electron transport (ETRmax), IK and effective photochemical quantum yield of PSII (Y(II)), indicating differences in the efficiency of photosystem II (PSII). Under At + 10 °C conditions, there were significant interactions in the minimum fluorescence in the dark-adapted state (F0), ETRmax, IK, Y(II), Ψs and photochemical quenching (qP and qL). Thus indicating that when subjected to the two combined stresses (WD − At + 10 °C) the cultivars showed different responses in the efficiency and operation of PSII. The results of this study indicate that the fluorescence parameters provide a good tool for phenotyping in blueberry breeding programs and enable the detection and elimination of unwanted genotypes at the beginning of the selection process.