Araceli Barceló-Muñoz

Micropropagation of adult avocado

A procedure has been developed to successfully micropropagate the IV-8 selection, an adult avocado rootstock. Cultures were initiated from basal shoots obtained after pruning a tree back to ground level. Buds sprouted in Murashige and Skoog solid medium with macroelements at half strength and a 1.3 μM benzyladenine supplement. To induce proliferation, shoots were cultured for 2 weeks in liquid medium in a rollordrum with the Gamborg salt formulation and 1.3 μM benzyladenine, followed by 6 weeks in double phase conditions (solid medium with a layer of liquid medium on the top) using the same salt formulation and two different benzyladenine supplements, 2.8 μM in the solid phase and 0.4 μM in the liquid phase. Ninety percent of the shoots rooted after a 3-day culture in liquid medium in a rollordrum with MS macroelements at 0.3× and 4.9 μM indolebutyric acid, followed by transfer to solid medium in the absence of auxin but with 1 g l−1 activated charcoal. Survival rate during the acclimatization in the greenhouse was 70%.

Variations in storage protein and carbohydrate levels during development of avocado zygotic embryos

Variations in carbohydrates and proteins were monitored during avocado (Persea americana Mill.) zygotic embryo development and correlated with growth parameters in order to define specific markers characterizing distinct embryogenic phases. Hexose (glucose and fructose) levels were initially high and declined as embryo development advanced reaching the lowest levels in completely mature embryos. Sucrose and starch evolution showed an opposite trend with a progressive increase during embryo growth. The beginning of the maturation phase could be identified by a switch in the carbohydrate status from high hexose/sucrose ratio to low hexose/sucrose ratio. Storage protein accumulation began at early cotyledonary stages (7–8 mm), increasing significantly in the maturation phase where they represented 83% of total proteins. Mature embryos (38–40 mm) contained albumins, globulins and glutelins, albumins being the predominant and most heterogeneous fraction. Storage protein accumulation occurred in a sequential and specific way suggesting a possible role as indicators of embryo development. The complete maturation stage could be characterized by the synthesis and accumulation of a 49 kDa albumin.

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 consistency, double phase and solid medium, at three different irradiance levels: 35, 60 and 85 μmol m−2 s−1. Effects of culture and environmental conditions in multiplication rate, rooting capacity, hyperhydricity and leaf 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 affected by these treatments but stomatal density was, interacting with the amount of irradiance applied. Increasing irradiance decreased concentration of chlorophyll a and carotenoids in the leaf but did not affect leaf hyperhydricity.