Discrimination of olive genotypes tolerant to drought based on their physiological mechanisms

Extreme climatic conditions such as high temperatures combined with increased water stress in the Mediterranean basin olive trees have raised the necessity to identify drought-tolerant olive tree genotypes. In a field experiment in 2020, we aimed to unravel the photosynthetic response of olive cultivars to drought stress. Ten Greek olive cultivars (‘Amfissis’, ‘Chondrolia Chalkidikis’, ‘Gaidourelia’, ‘Kalamon’, ‘Kerkyras’, ‘Koroneiki’, ‘Koutsourelia’, ‘Mastoidis’, 'Valanolia', and ‘Megaritiki’), one from Italy (‘Frantoio’) and one from Spain (‘Picual’) were evaluated for their photosynthetic performance under well-irrigated and non-irrigated conditions. The net photosynthetic rate (P_n) and intercellular CO₂ (C_i) were significantly affected by genotype, irrigation conditions, and their interaction. Conversely, stomatal conductance (g_s) and transpiration (E) followed a different trend. Specifically, the genotype affected g_s and E, while irrigation conditions and the interaction of both factors did not show significant differences on these photosynthetic parameters. P_n of (‘Picual’) and ‘Valanolia’ increased by 53 and 72% under irrigation, respectively. ‘Koutsourelia’ showed the highest values regarding photosynthetic parameters, though ‘Valanolia’ showed the highest value of intercellular CO₂ assimilation. ‘Valanolia’, ‘Kerkyras’ and ‘Koroneiki’, ‘Mastoidis’, and ‘Kerkyras’ exhibited the lowest P_n, g_s, C_i assimilation, and E, respectively. These findings highlight the need for further research investigations on the different physiological responses of genotypes to drought stress.