MYCORRHIZAL DEPENDENCY OF MICROPROPAGATED ARGAN TREE (ARGANIA-SPINOSA) .1. GROWTH AND BIOMASS PRODUCTION

The influence of V.A. mycorrhization was studied on two clones of in-v itro micro-propagated plantlets of Argania spinosa, a slow-growing tre e of great importance in agroforestry systems in the semi-arid and ari d zones of southwestern Morocco. Inoculation increased total shoot len gth, stem girth and biomass of the plants, when cultivated in controll ed conditions with a phosphorus fertilization of 31 mgP.kg-1 added to a substrate already containing 13.5 mg.kg-1 available P (Olsen). The p ositive effect increased with time and, after 6 months, the above-grou nd dry matter production was 5 to 6 times higher for inoculated plants . The Relative Mycorrhizal Dependency Index, calculated on total dry m atter, reached 77-78% at the end of experiment. Calculated on above-gr ound dry matter, the R.M.D.I. was 81-83%, placing the argan tree among the plants most dependent on mycorrhizal symbiosis. The root/shoot ra tio was markedly (40-50%) reduced by inoculation, demonstrating the hi gher efficiency of a mycorrhizal root system.