367 Ex Vitro Mycorrhization of Vitro-Derived Plantlets of ‘Carrizo’ Citrange [C. sinensis (L.) Osb. × P. trifoliata (L.) Raf.] B. Chiancone, F.G. Casales, V. Mondello, L. Torta, S. Burruano and M.A. Germanà Dipartimento di Scienze Agrarie e Forestali Università degli Studi di Palermo Italy Keywords: arbuscular mycorrhizal fungi, ‘Carrizo’ citrange, Citrus rootstocks, micropropagation, mycorrhization Abstract In this study, vitro-derived plantlets of ‘Carrizo’ citrange were inoculated with Glomus intraradices during the acclimatization phase, from in vitro to in vivo. Plantlets were grown in presence (+M) and in absence of inoculum (-M) and in addition, in sterile and non-sterile substrate. After three months of culture, some vegetative parameters and the level of infection, varied greatly in the different theses. In particular, the highest formation of new branched roots has been observed in inoculated plantlets cultivated in sterile substrate. Good results were observed also in non-inoculated plantlets cultivated in non-sterile substrate, in presence of endemic inoculum. The same trend was observed analyzing the mycorrhizal infection. In fact the highest level of mycorrhization was observed both in inoculated plantlets in sterile substrate and non-inoculated plantlets in non-sterile thesis. Although the symbiosis induced a better growth of the rooting apparatus, results confirmed the low mycorrhizal-dependence of citrange, also regarding in vitro- derived plantlets. INTRODUCTION Arbuscular mycorrhizae (AM) are endomycorrhizae produced by fungi belonging to the division Glomeromycota, genera Acaulospora, Gigaspora, Glomus, Sclerocystis and Scutellospora. Those fungi colonize at inter- and intracellular level the root epidermal and cortical parenchyma of most plant species. In this mutualistic association, the extended extramatrical mycelial system develops in the soil, improving soil structure and capturing different mineral ions and elements (particularly, phosphorus). Inorganic matter is moved in the mycelial intramatrical phase, characterized by intra- and intercellular structures, as vesicule, hyphal coils and arbuscules and, then, released into the root cells. Vice versa, the photosynthesis products, transmigrating from the host leaves to the roots, become available for the mycorrhizal fungus and uptaken by intracellular arbuscules. The AM beneficial role for plants has been demonstrated by several studies; in fact, the symbiosis ensures nutritive component supply and induces tolerance to root pathogens and abiotic stresses. (Schenck, 1981; Harley and Smith, 1983; Abbott and Robson, 1986; Pfleger and Lindermann, 1996). The AM presence in Citrus was described, for the first time, in 1933 (Reed and Freemont, 1935); later it was observed that mycorrhizae are very useful for mineral and water nutrition in Citrus and other similar plants, characterized by relatively coarse root system and low efficiency in the nutrient supply (Baylis, 1970; Menge et al., 1978; Nemec, 1978; Syvertsen and Graham, 1999). The mycorrhizal-dependence of Citrus can greatly vary depending on genotype, type of soil and efficiency of the fungus (Cardoso et al., 1986; Dutra et al., 1996; Graham and Syversten, 1985; Nemec, 1977; Raman and Mahadevan, 1996; Vinayak and Bagyaraj, 1990). Nemec (1978), studying the influence of AM on the growth of different Citrus rootstocks, observed that ‘Troyer’ citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] was the least dependent on the association. To date, citranges are the most widespread Citrus rootstock, because of the good quali-quantitative characteristics induced to the fruits and of their tolerance to the Citrus Proc. VIII th IS on In Vitro Culture and Horticultural Breeding Eds.: J.M. Canhoto and S.I. Correia Acta Hort. 1083, ISHS 2015