Study on pecan seed germination influenced by seed endocarp

Nondeep physiological dormancy exists in freshly harvested pecan (Carya illinoinensis) seed, and the endocarp inhibits the seed germination. New methods were tried to detect if “chemical dormancy” or “mechanical dormancy” was caused by the endocarp. The germination of freshly harvested pecan seed with the removal of different parts of the endocarp and the fracture pressure of the endocarp of pecan seed soaked in water at different temperatures were tested. The results showed that (1) there was no significant difference in germination rate between the pecan kernel keeping in touch and out of touch with the same part of the endocarp, (2) whether a part of endocarp was removed to expose the radicle, preventing endocarp from splitting by glue inhibited the radicle elongation significantly, (3) the fracture pressure of the endocarp decreased significantly over water uptake time, and (4) little difference in the fracture pressure of the endocarp between different soaking temperatures. In conclusion, it suggested that (1) the endocarp caused “mechanical dormancy” but “chemical dormancy,” (2) the prevention of radicle elongation was due to the endocarp pressuring the cotyledon rather than the direct physical restriction on the radicle, and (3) the radicle elongation seemed to be able to respond to the suture split and the pressure on the cotyledon.