Genotypic differences relative photochemical activity, inorganic and organic solutes and yield performance in clones of the forage cactus under semi-arid environment.

Plants with the crassulacean acid metabolism commonly present good adaptation to arid and semi-arid environments, but it highly depends on the type of species. In this study, chlorophyll fluorescence, the concentration of inorganic and organic solutes and the productive performance were evaluated along with their relationships in different clones of the genera Opuntia and Nopalea. The experiment was conducted from 2016 to 2018. Four clones of genus Opuntia were evaluated: 'Orelha de Elefante Mexicana' (OEM), 'Orelha de Elefante Africana' (OEA), V19 and F8; and two clones of genus Nopalea: 'IPA Sertânia' and 'Miúda'. The experiment was arranged in a randomised block design, with six treatments and three replications. The following parameters were measured when harvesting: initial, maximum and variable fluorescence; the quantum yield of PSII (Fv/Fm); light-induction curves of the photochemical parameters (ΔF/Fm', qP, NPQ and ETR); the chlorophyll and carotenoid content; carbohydrates; the sodium (Na) and potassium (K) content; morphometry; and dry matter accumulation. The values for the effective quantum yield of PSII (ΔF/Fm') and the alterations in photochemical quenching were higher in the OEM clone (P < 0.05). There was a difference between clones for non-photochemical quenching, with the F8 clone having the highest values. The Fv/Fm was 0.87 for the OEM. 'IPA Sertânia' obtained the greatest Chl a/b, and the highest values for carbohydrate concentration were found in the OEA clone. The OEM clone showed the greatest accumulation of K, in addition to a higher cladode area index and greater dry matter accumulation. The results of this study show the high physiological tolerance of the forage cactus to a semi-arid environment, which varies according to the clone.