In vitro rescue of immature avocado (Persea americana Mill.) embryos

An in vitro culture protocol was developed as a means of avocado embryo rescue. Different factors including presence of cotyledons, medium texture and cold or gibberellic acid pretreatments, were studied. To better understand the germination process in this recalcitrant species, immature zygotic embryos at different stages were used in these experiments. Optimum results were dependant on the embryo developmental stage. Whereas smaller embryos (5 mm long) germinated better in M1 liquid medium, 15 mm long embryos responded better when precultured in B5m medium supplemented with 1 mg l−1 GA3, and fully mature embryos were capable of germinating directly in solid M1 medium. Our results suggest the existence of two types of dormancy in avocado embryos: an embryo-dormancy caused by cotyledons, and another type of dormancy, mainly occurring in 35 mm long embryos and revealed by the formation of dwarfing rosette seedlings, that can be released by a GA3 pretreatment.