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