“…Among the factors influencing the somatic embryogenesis initiation, the appropriate developmental stage of zygotic embryos seemed the most critical. The optimal developmental stage for many conifer species has been reported in terms of seed collection date or time after fertilization (Becwar et al, 1990;Tautorus et al, 1991;Lelu et al, 1994b;Jain et al, 1995;Zoglauer et al, 1995;Lelu et al, 1999;Kim et al, 1999). However, due to the difficulty in determining the precise time of fertilization in open-pollinated cones and the fact that the variation in the zygotic embryo development depends on weather and location, the criteria for explant collection for ECI cannot be easily generalized.…”