Comparative study of leaf physiological and biochemical characteristics in commercial and traditional Prunus dulcis (Mill.) Rchb. cultivars under rain-fed conditions

Drought is the major abiotic stress in agriculture, and enhancement of plant characteristics under this stress is one of the major goals behind plant breeding. Almond is a drought-tolerant species, but, when water supply is not limited, it presents increased performance. To overcome the lack of water availability, the correct selection of cultivars is of great importance, as different responses of various almond genotypes have been reported in relation to drought stress. Hence, the present work aims to characterize leaf traits of several Portuguese traditional almond cultivars ('Bonita', 'Casanova', 'Parada', 'Pegarinhos' and 'Verdeal'), comparing them to two foreign cultivars ('Ferragnes' and 'Glorieta'). For this, leaf gas exchange, sclerophylly, leaf water relations parameters, photosynthetic pigments and total phenolic content were studied in 2017 and 2018, years that presented contrasting weather conditions. Several significant differences on leaf traits were found, particularly in relative water content, leaf mass per area, photosynthetic rate or stomatal conductance. Besides a clear effect of the cultivar, the sampling year also significantly influenced results, although not in all the parameters under study. The results obtained show a complex behavior of almond trees under rainfed conditions, but highlight some potential drought resistance in Portuguese cultivars, namely 'Casanova' and 'Parada' that should be further studied.