Effect of culture media and irradiance level on growth and morphology of Persea americana Mill microcuttings

Avocado shoots were multiplied in vitro in two culture media of different c onsistency, double phase and solid medium, at three different irradiance le vels: 35, 60 and 85 mu mol m(-2) s(-1). Effects of culture and environmenta l conditions in multiplication rate, rooting capacity, hyperhydricity and l eaf surface morphology of microcuttings were evaluated. Double phase medium induced hyperhydricity, producing leaf microcuttings with deformed stomata and low crystalline epicuticular waxes; microcuttings also showed reduced rooting capacity. By contrast, solid medium promoted leaf area development on microcuttings and decreased hyperhydricity. Stomatal index was not affec ted by these treatments but stomatal density was, interacting with the amou nt of irradiance applied. Increasing irradiance decreased concentration of chlorophyll a and carotenoids in the leaf but did not affect leaf hyperhydr icity.