Improvement of plant recovery from avocado zygotic embryos by desiccation under high relative humidity conditions

Due to the high fruit abscission characterizing avocado, protocols for immature embryo rescue are an important tool in breeding programs based on hybridization of elite genotypes. The objective of this investigation was to evaluate the effect of in vitro desiccation under high relative humidity conditions on immature avocado embryo germination. The duration of the desiccation treatment significantly affected embryo germination, with optimum results achieved after a 14-day treatment (66.7% in desiccated embryos versus 15% in control, non treated embryos). Other traits, such as recovery of complete plants and quality of the obtained plants, were also improved following desiccation. Trying to reproduce the final stages of avocado zygotic embryogenesis, the effects of desiccation after an in vitro maturation treatment was also evaluated. Results obtained revealed a significant effect of maturation stage, desiccation and the interaction between both factors; e.g., while desiccation significantly improved germination after in vivo maturation, a slight decline was observed in in vitro matured embryos, probably due to differences in embryo water status. However, recovery of complete plants and length of the structures formed were only significantly affected by maturation stage. Nevertheless, in embryos directly coming from trees, in vitro drying significantly improved rescue in all cases, independently of embryo developmental stage. Therefore, desiccation under high relative humidity conditions can be considered a valuable tool to be used in protocols for avocado embryo rescue. However, its use in conjunction with in vitro maturation treatments is not recommended.