Water stress affects leaf anatomy, gas exchange, water relations and growth of two avocado cultivars

Two cultivars of avocado (Persea americana Mill., 'Fuerte' and 'Hass') plants, grown in 501 containers, were studied under two irrigation regimes for 6 months in order to evaluate the growth response and leaf physiological and anatomical changes induced by moderate water stress. Irrigation was applied when soil water potential reached at -0.03 and -0.5 MPa for the wet and dry treatments, respectively. Leaf anatomy changed in water-stressed leaves, which could have accounted for the decreased stomata] conductance. Photosynthesis is inhibited by reducing the diffusion of CO2 to the chloroplast, both by stomata] closure and changes in mesophyll structure, which decreases the conductance to CO, diffusion within the leaf. Predawn leaf water potential (psi) declined by 0.9 MPa for 'Fuerte' and 1.2 MPa for 'Hass' after 12 days of withholding water, whereas the turgor potential (psi(p)) remained positive due to a decrease in the osmotic potential (psi(pi)) in both cultivars. The reduction in osmotic potential was mainly due to dehydration and only partly related to active accumulation of solutes. Tissue elasticity seems to be the predominant physiological mechanism of drought adaptation of avocado. Growth data suggests that 'Hass' seems to be more affected by moderate water stress. (C) 2002 Elsevier Science B.V All rights reserved.