Germination Protocol for Cedar Walnut Seeds (Juglans pyriformis Liebm.) Using Thermal Shock

Juglans pyriformis Liebm. (Juglandaceae) is a species endemic to Mexico, which inhabits the mesophyll mountain forest and is highly valued for the quality of its wood. Therefore, it has been overexploited and its population has declined; it is currently listed as endangered. Therefore, it is important to implement conservation measures. One conservation strategy could be to collect seeds in tree for the establishment of forest plantations. Another strategy is to conserve them in vitro germplasm banks through the propagation and establishment of vegetative explants. Under natural and nursery conditions, Juglans pyriformis seeds require constant humidity to germinate, which is very late and slow due to the physical barrier posed by the hard pericarp. Likewise, when seeds of this species are germinated in laboratory, pre-germination treatments must be applied to promote germination and obtain plants for the propagation and conservation this species using in vitro techniques. The application of a thermal shock by subjecting the seed to 30 s in liquid nitrogen and immediately after another 30 s in boiling water is an effective treatment to promote germination in seeds of this species.