Physiological and morphological responses to mineral (N, Mg, Mn, Zn) stress in pear (Pyrus communis L.) cultivars “Meski Ahrech” and “Alexandrine”

Abstract

The effect of nutrient deficiencies on growth, photosynthetic activity, and water status was studied in two cultivars of pear trees, local cultivar Meski Ahrech and an introduced cultivar Alexandrine. Plants were irrigated with a nutrient solution to induce N, Mg, Mn, and Zn deficiencies. Tree height (PH) was higher in Meski Ahrech than Alexandrine under nutritional stress treatments. However, the average leaf area (LA) of both cultivars was not affected by any nutritional stress treatments. As expected nutrient deficit stress reduced chlorophyll index (SPAD), net photosynthesis (AN) in both cultivars, and as result it reduced stomatal conductance (gs) comparing to control treatments. Relative water content (RWC) was maintained almost in the same value in all the treatments and in both cultivars. Leaves were sampled periodically to determine leaf-nutrient concentration. Alexandrine appeared more sensitive to N, Mg, Mn, and Zn deficiency due to the main decrease in growth, AN and SPAD and gs compared to Meski Ahrech. When a symptom appeared, the symptomatic leaves were collected to be photographed. Deficiency symptoms appeared in the range of 66 d after treatments for N and in 94 d for Mg, Mn, and Zn. Leaf-nutrient concentrations to which the symptoms appeared were determined in these two cultivars: leaf N concentration was around 1.6%, leaf Mg concentration was 0.5% in Meski Ahrech, and 0.4% in Alexandrine. Leaf Mn concentration was 30 ppm in Meski Ahrech, 21 ppm in Alexandrine and finally leaf Zn concentration was 15 ppm in Meski Ahrech and 17 ppm in Alexandrine. We deduced that Meski Ahrach is more efficient for mineral nutrition uptake and that Alexandrine exhibited a more conservative strategy with all treatments.