Evaluation of the resistance of few citrus rootstocks to alkalinity by applying a faste test of secreening

Alkalinity of Moroccan soils is the major abiotic constraint on citrus production area. The best choice of citrus rootstocks adequate and resistant is a better solution to avoid this problem. The aim of this study is to develop a fast test of citrus rootstocks screening towards alkalinity. The alkaline stress was applied on ten citrus rootstocks two month old, using irrigation with a Hoagland and Arnon solution added with 1 g CaCO(3)/L and adjusted at various pH levels 6, 7 and 9. Observations concerned symptoms incidence and severity of iron chlorosis after two months of rearing. Results permitted to classify Poncirus trifoliata and Flying dragon as the most sensitive to alkalinity stresses, whereas, Citrus volkameriana and Citrus macrophylla were resistant. These conclusions are equivalent with those obtained with old citrus rootstocks in field trials

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

Évaluation de la résistance de dix porte-greffes d’agrumes résistants à la tristeza vis-à-vis du déficit hydrique

Introduction. In Morocco, citriculture faces up an increasing combination of biotic (Citrus tristeza virus (CTV) / Phytophthora spp.) and abiotic stresses (salinity, alkalinity and drought). Most of these constraints should be individually managed by adapted rootstock choice. However, the spread of CTV in the Mediterranean Basin will soon prohibit the use of the traditional sour orange rootstock, which currently provides sufficient tolerance to salinity and alkalinity. Therefore, the selection of new citrus rootstocks becomes urgent. Our study sought to investigate the effect of different water regimes on growth of ten citrus rootstocks: citrange Carrizo (France), citrange Carrizo (Morocco), citrange Troyer, citrange Yuma, Citrus volkameriana; two Poncirus trifoliata of different origins, citrumelo, Mand. Sunki x Poncirus trifoliata, and Poorman. Materials and methods. For each rootstock, three months old seedlings were grown in plastic pots (0.5 L) in a greenhouse at El Menzeh, INRA, Morocco; they were subjected to three water regimes [(100%, 75% and 50%) moisture field capacity (Hcc) of the substrate]. The experiment was arranged in a split-plot design with three treatments. The morphological parameters measured were the plant height and dry and fresh matter accumulation. Physiological parameters studied were the Relative Water Content, transpiration rates and chlorophyll, soluble sugars and proline contents. Results. The morphological and physiological parameters were affected by the intensity of water stress applied. However, rootstocks behaved differently regarding to this constraint. Water stress induced an increase in the proline and soluble sugars content in the rootstock leaves. Conclusion. Water stress significantly affects the physiological and morphological characteristics of citrus rootstocks and, in conditions of extreme water deficit (50% Hcc), a differential behavior of the rootstock was found. Based on our results, the rootstocks Carrizo citrange (Morocco) and Poorman present the best overall ability to withstand water stress

Response to drought stress of 'Sidi Aissa' clementine (Citrus reticulata Swingle) grafted on five citrus rootstocks

In Morocco, most citrus orchards are planted in the semi-arid area where water is scarce. Furthermore, Moroccan citrus orchards face increasing combinations of biotic (Citrus tristeza virus (CTV) / Phytophthora spp.) and abiotic stress (salinity, alkalinity and drought). Drought in citrus affects plant morphology and physiology, and ultimately leads to yield reduction. Growth, morphological and physiological parameters were monitored, to assess the effect of drought stress on young citrus plants of ‘Sidi Aissa’ Clementine variety grafted on five citrus rootstocks (Citrus macrophylla, C. volkameriana, Mand. Cleo. X CC 30577, Carrizo and Troyer citrange). The experiment was performed under controlled drought conditions on two-year old trees. Two treatments were applied for each rootstock: a control treatment, irrigated at 100% Hcc (field capacity), and a stress-treatment, irrigated at 50%Hcc. Drought stress affected all parameters under consideration. Under stress conditions, ‘Sidi Aissa’ grafted on citrange Carrizo, C. macrophylla and C. volkameriana produced larger canopy sizes than trees grafted on other rootstocks, whereas Cleo. X CC 30577 had the lowest tree canopy volume. This study showed that Carrizo citrange, C. macrophylla and C. volkameriana are the better rootstocks for ‘Sidi Aissa’ Clementine grafting under drought conditions

Screening of ten citrus rootstocks to drought stress

In Morocco, citrus orchards are planted in different areas with various soils and climates. The majority occurs in dry areas so that irrigation is necessary in order to assure adequate production. The spread of CTV in the Mediterranean Basin will soon prohibit the use of the traditional sour orange(Citrus aurantium) rootstock, which currently provides tolerance to soil drought, salinity and alkalinity. It is therefore imperative to develop and select new citrus rootstock. Our study sought to investigate the effect of different watering regimes on growth of ten citrus rootstock candidates. Ten citrus rootstocks, i.e. Citrumelo Winter Haven B2 31431, citrumelo 4475 B2G3, Mandarine sunki X Poncirus trifoliata 30591, Mandarine cléopâtre X Poncirus trifoliata 30585, sour orange (Citrus aurantium), Poorman B2 C3, Mandarine Sunki X Poncirus trifoliata B2 30581, citrange Carrizo ((Citrus sinensis x Poncirus trifoliata ), Poncirus trifoliata and Citrus volkameriana were subjected to different levels of drought stress to study their morphological and physiological responses. For each rootstock, three months’ old seedlings were grown in plastic pots (0.5 L) in a greenhouse at El Menzeh, INRA Morocco. They were subjected to three watering regimes (100%, 75% and 50% of moisture field capacity (Hcc) of the substrate). The experiment was arranged in a split-plot design with three repetitions. Observations on plant height; dry and fresh matter accumulation, Relative Water Content (RWC), transpiration rate (T) and chlorophyll, soluble sugars (TSS) and proline contents were recorded. We recorded reduction in plant height and dry and fresh matter accumulation, relative water content (RWC), transpiration rates (T) and chlorophyll contents with increasing drought stress for all rootstocks tested. Drought stress significantly affects the physiological and morphological characteristics of citrus rootstocks and, in drought conditions a differential behaviour of the rootstock was found. Based on our results, rootstocks Mandarine Sunki X Poncirus trifoliata B2 30581, citrange carrizo, sour orange (Citrus aurantium) and Citrumelo Winter Haven B2 31431 present the best overall ability to withstand drought stress

Effect of flooding on four citrus rootstocks (two sour oranges (Citrus aurantium L.) and two citranges [Citrus sinensis (L.) Osb. x Poncirus trifoliata (L.) Raf])

The effects of flooded soil on chlorophyll content and vegetative growth were studied in four potted six months–old citrus rootstock seedlings: Citrus aurantium L. var gou tou (GT), Moroccan sour orange (C. aurantium L.) (SO), Troyer (CT) and Carrizo (CC) citrange (C. sinensis (L.) Osb.xPoncirus trifoliata L.). Each rootstock seedling was grown in a black plastic bag in a greenhouse at El Menzeh, INRA Morocco. Plants were submitted outdoors to four treatments: T0, not flooded (control); and three flood treatments by submerging pots in 10L containers filled with tap water; during 3 (T1), 6 (T2) and 60 (T3) days. For each rootstock, stem diameter, plant height and number of leaves were measured in the beginning and at the end of the experiment. Root and shoot dry weight and leaf chlorophyll content were measured at the end of the experiment. After 60 days, relative growth, number of leaves, plant height, fresh total biomass, dry total biomass and leaf chlorophyll content had significantly decreased by flooding (respectively by 50%, 30%, 50%, 47%, 42% and 58%). Our study shows that the CC and CT rootstocks were the most-tolerant to flooding. The latter seedlings grew better and accumulated more chlorophyll and dry biomass, and had a higher number of leaves than the other seedlings in different flood stress treatments. Results indicate that Carrizo and Troyer citrange are more appropriate rootstocks than Gou-Tou and Moroccan SO to tolerate occasional soil flooding situations