Effet de la nutrition azotée sur les paramètres morphologiques et physiologiques de quelques portegreffes d’agrume

Introduction: In Morocco, the sour orange is the rootstock the mostly used in citrus orchard. This position is acquired because of its good adaptation vis-à-vis the Moroccan soil conditions of the regions characterized by the high alkalinity and salinity. However, the spread of CTV in the Mediterranean Basin will soon prohibit the use of traditional rootstock (sour orange). Therefore, the profile of plant material used for the planting of new citrus orchards is changing. To date, studies dealing with the optimization of nitrogen fertilization and selection of the most efficient rootstock in terms of nitrogen use in the production of citrus plants in good quality at the nursery are very important. To finalize the selection of rootstocks revealing performance in terms of adaptation to soil and climatic conditions, their evaluation on the efficiency of input use is of paramount importance. Objective: The main objective of this study is the evaluation of the alternative rootstocks to sour orange (Citrus aurantium L.) in terms of nitrogen usage. Material and methods: This study was carried out in greenhouses at the Experimental station of El Menzeh INRA Morocco. The six rootstocks tested are: citrange Carrizo, citrange C35, Citrus volkameriana B2 28613, Citrus macrophylla, Citrumelo 4475 AB6 A4 and sour orange (Citrus aurantium L.). These seedlings rootstocks aged three months were grown in plastic pots (3L). Nitrogen was added to the nutrient solution modified Hoagland and Arnon (1950), at four doses: T1 (0 mM of N), T2 (1 mM N), T3 (5 mM N) and T4 (10 mM N) for each rootstock. Different doses of nitrogen were applied once a week over a period of three months at 0.5 liter per plant. The experimental design adopted was a split-plot design with three replications. Results: The results of this study showed that there is variability in response between the rootstocks studied vis-à-vis the nitrogen.Citrus volkameriana B2 28613, Citrus macrophylla and Citrumelo 4475 AB6 A4 recorded the highest values of number of leaves per plant, diameter of the collar, the final height of the stem, total leaf area and fresh and dry weight of different organs (stem, leaves and root). Citrus volkameriana B2 28613 and Citrus macrophylla showed the highest percentages of relative water content. The rootstock Carrizo citrange showed the highest content of total chlorophyll (SPAD) and total soluble sugars (TSS). Also, Citrus macrophylla had the stomatal conductance and concentration of the highest total chlorophyll in leaves. Citrus volkameriana B2 28613 and Citrus macrophylla have accumulated higher levels of nitrogen in leaves. Conclusion: Citrus volkameriana B2 28613, Citrus macrophylla and citrumelo 4475 AB6 A4 rootstocks are most efficient in terms of nitrogen use in the nursery stage and that the dose T3 (5 mM of N) proved to be optimal for the production of good quality plants to rootstocks at nursery stage