Water relations in culture media influence maturation of avocado somatic embryos.

Application of transformation and other biotechnological tools in avocado (Persea americana Mill.) is hampered by difficulties in obtaining mature somatic embryos capable of germination at an acceptable rate. In this work, we evaluated the effect of different compounds affecting medium water relations on maturation of avocado somatic embryos. Culture media were characterized with respect to gel strength, water potential and osmotic potential. Improved production of mature somatic embryos was achieved with gelling agent concentrations higher than those considered standard. The osmotic agents such as sorbitol and PEG did not have positive effects on embryo maturation. The number of w-o mature somatic embryos per culture was positively correlated with medium gel strength. Gel strength was significantly affected by gelling agent type as well as by gelling agent and PEG concentration. Medium water potential was influenced by sorbitol concentration; incorporation of PEG to a culture medium did not affect medium water potential. The highest maturation results were achieved on a medium gelled with 10 gl(-1) agar. Moreover, these somatic embryos had improved germination rates. These results corroborate the role of water restriction as a key factor controlling maturation of somatic embryos.