LEAF MORPHOLOGY, SCLEROPHYLLY AND LEAF WATER RELATIONS OF SOME FIELD-GROWN OLIVE (OLEA EUROPAEA L.) CULTIVARS IN TUNISIA

With the increasing effect of global warming, olive growing is facing very severe conditions. In Tunisia, the rainfall deficit reached in some areas more than 50% of the normal amount and the temperature rose considerably. The present study was conducted in order to understand the behavior of the olive trees to these changes. We found considerable morphostructural leaf differences among the cultivars. Based on the study of leaf structure, ‘Dahbia’ leaves showed the highest value of ratio (palisade/spongy parenchyma). So, this cultivar enhanced its sclerophylly by building parenchyma tissues. Also, ‘Besbessi’ showed the lowest total lamina with high value of leaf stomatal resistance. In fact, to cope with the environmental stress conditions and water scarcity, olive cultivars used different strategy to overcome the surrounding circumstances. ‘Fougi’ showed the lowest relative water content when ‘Lucques’ exhibited good protection against water loss through the lowest values of water saturation deficit associated to the low values of stomatal resistance and leaf water potential. Concerning the chlorophyll fluorescence, the maximum quantum yield as the ratio Fv/Fm revealed that, for all studied cultivars, the functional integrity of photosystem II was not affected. The results obtained indicated good plasticity of olive leaves to cope with stress. The leaf mechanisms employed are very various (morpho-structural and ecophysiological) and differ from cultivar to another.