Influence of the Mycorrhizal Glomus intraradices on the Development of In Vitro Raised Olive Seedlings During Acclimation Phase

For olive genetic improvement work it is very important to obtain a high rate of seed germination and a shortening of the juvenile period of the plants raised. By in vitro embryo culture, a 100% of germination is attained in a few days and the supply of adequate nutritive solutions and photoperiod speeds up seedling development during hardening, thus shortening juvenility. Mycorrhizal is another resource to improve plant development. This work attempts to know the effect of the vesicular-arbuscular mycorrhizal Glomus intraradices on the survival and development of olive seedlings obtained by in vitro embryo germination, during greenhouse hardening phase. Olive seedlings obtained by in vitro embryo germination were transplanted to pots with sterile sandy soil. Half of the pots were inoculated with 5g of Glomus intraradices. Afterwards, the pots were transferred to a greenhouse and watered at field capacity. After 180 days in this conditions, the number of dead plants, stem and shoot length of the surviving plants, and leaves, stems, shoots, roots and whole plant fresh and dry weight were recorded. Also, the nutritive status of the above indicated organs was analysed. N was determined by Kjeldahl digestion and mineral nutrients (P, K, Ca, Mg, Fe, Mn, Cu, Zn) by ICP-OES. Soil texture was determined according to the method of Gee and Bauder (1986) and chemical fertility according to Page et al. (1982). The treatment with mycorrhizal fungus Glomus intraradices significatively increased (from 71 to 88%) the number of surviving plants after ex vitro transfer. The effect of the symbiosis plant-fungus was even more spectacular on the development of the surviving plants, three-folding fresh weight, dry weight and plant size (from 6 to 18 g, 2.5 to 7.6 g and 31 to 91 cm, respectively) after 180 days of culture. The better growth of the treated plants coincided with a higher nutrient acquisition, particularly P, in a low chemical fertility medium, as was the substrate used. INTRODUCTION For the olive breeding works it is very important to reach a high proportion of seed germination and a shortening of the juvenile improductive phase. By in vitro culture of isolated mature olive embryos very high germination percentages have been obtained (Troncoso et al., 1991; Voyiatzis and Pritsa, 1994; Voyiatzis, 1995) in few days, even reaching 100% (Acebedo et al., 1997) and by using appropriate nitrogen forms and concentrations (García et al., 1994; Sarmiento et al., 1994) and sugar (García et al., 2002) a high in vitro growth of the seedlings was obtained. The use of a suitable substratum (Rugini, 1984), nutritive solutions (García et al., 1999) and photoperiod (Alvarado, 1994) during the hardening phase also increases the plant development. With the plants in the field, pruning and cultivation conditions also influence their growth speed (Lavee, 1990; Lavee et al., 1996; García-Ortiz et al., 2001; Navarro and Parra, 2001). Due to the