Type 2 Nondeep Physiological Dormancy in Seeds of Fraxinus chinensis subsp. rhynchophylla (Hance) AEMurray

Fraxinus chinensis subsp. rhynchophylla (Oleaceae), hereafter F. rhynchophylla, is an important timber species in northeast China; however, little is known about its seed dormancy and germination, which hinders regeneration of the species from seeds for reforestation and conservation. Our aim was to determine the class of seed dormancy and how to break it. Studies were conducted to determine the permeability of the seed coat to water, changes in embryo development during cold stratification and effects of cold stratification on germination over a range of temperatures. The seeds were water-permeable, and the embryo was fully developed and filled the embryonic cavity. Cold stratification at 5 degrees C for 8 weeks was effective in breaking dormancy; thus, we conclude that the seeds have nondeep physiological dormancy (PD). As cold stratification time was increased, the ability of seeds to germinate at low temperatures (e.g., 10 degrees C and 15 degrees C) increased, indicating the presence of Type 2 nondeep PD, in which the minimum temperature for germination decreases during dormancy-break. Nondormant seeds germinated to high percentages and rates at constant temperatures of 25 degrees C (germination percentage was 63%) and at alternating temperature regimes of 35 degrees C/25 degrees C, 30 degrees C/15 degrees C, 25 degrees C/20 degrees C and 20 degrees C/10 degrees C (germination percentage was 66%, 67%, 65% and 66%, respectively). To produce seedlings, we recommend 8 weeks of cold stratification at 5 degrees C before sowing the seeds at temperatures ranging from 15 degrees C to 30 degrees C.