Using chlorophyll fluorescence, photosynthetic enzymes and pigment composition to discriminate drought-tolerant ecotypes of <it><bold>Argania spinosa</it></bold>

The objective of our present study was undertaken to identify and to discriminate the tolerant ecotypes of Argania spinosa in terms of drought tolerance by studying the change of chlorophyll fluorescence traits, chlorophyllase and Ferredoxin-NADP(+)-oxidoreductase (FNR) activities and pigment composition. A. spinosa plants corresponding to four contrasting ecotypes (Rabia, Admine, Aoulouz and Lakhssas) were exposed to drought stress. Under severe drought conditions (25% of field capacity), we recorded a significant decrease in the maximum efficiency of PSII, the intrinsic efficiency of open PSII the coefficient of photochemical quenching (q(p)) and the quantum yield of PSII electron transport (phi(PSII)) (p<0.001). However, drought stress induced a significant increase in the coefficient of non-photochemical quenching. Positive and significant correlations were found between the ratio Chl a/b and chlorophyllase activity during the period of stress. Anthocyanin content and percentage of pheophytinization increased substantially in parallel with the severity of induced stress. Highest constitutive activity of FNR was recorded in the inland ecotypes (Lakhssas and Aoulouz). According to the canonical discriminant analysis, the four ecotypes have been separated mainly by the traits having the most discriminating power: phi(PSII), q(p), and anthocyanin content. Both inland ecotypes seem to be more drought tolerant and very promising for the regeneration of the Moroccan Arganeraie.