Effect of six rootstocks on leaf content of micronutrients (Fe, Zn, Mn, and Cu) in ‘Valencia’ orange trees under a calcareous soil

Citrus rootstocks differ substantially in their ability to acquire micronutrients from alkaline and calcareous soils. In this study, we aimed to evaluate this difference through leaf analysis of ‘Valencia’ orange trees grafted on six rootstocks (Sour orange, Citrange Carrizo 28608, Citrus volkameriana 28613, Citrus macrophylla, Citrumelo 4475 and Sunki mandarin × Poncirus trifoliate 30591) that are commonly used in citrus production in Morocco. The study was conducted in a citrus grove established since 1998 at the experimental Station of Sidi Allal Tazi (INRA, Morocco). The experiment was laid out in a completely randomized design with four replicates of each rootstock treatment. Soil of the experimental grove is classified as vertic cambisol with a clay loam texture, pH of 7.8, and a CaCO₃ content of 15%. Six- to seven-month-old leaves were collected and analyzed to determine their contents of Fe, Mn, Zn and Cu. Leaf analysis revealed a wide range of micronutrient content among the six rootstocks: Fe (26-81 ppm), Mn (6-22 ppm), Zn (7-19 ppm), and Cu (15-21 ppm). However, a statistically significant difference was only found in Fe content (P<0.001). ‘Valencia’ orange trees on Carrizo citrange had the highest leaf content of Fe, while those on citrumelo had the lowest content. Overall, ‘Valencia’ orange trees grafted on the three rootstocks Carrizo Sunki mandarin × Poncirus trifoliate, macrophylla, and volkameriana recorded the best performance in terms of leaf composition of the four studied micronutrients.