Effect of water stress on germination of beechnuts treated before and after storage

Beechnuts from two seedlots were pretreated, without medium, at a controlled moisture content (MC) of 30% before or after 1-year storage at –7 °C. Seeds treated with the two methods were germinated on substrates at decreasing osmotic potential down to –1.2 MPa. A moderate stress of –0.2 MPa caused a slight but significant decrease in germination percentage. Each further increment in water stress produced additional significant decreases in germination capacity. At –1.2 MPa, germination was almost prevented. Seeds pretreated before storage showed lower germination percentage and speed at all osmotic potentials, but this result was due to a marked effect of seed initial MC, rather than a lower resistance to water deficit. In fact, MC of beechnuts pretreated before storage was 8%, whereas beechnuts pretreated after storage started germination tests under water stress with an initial MC of 30%. Moreover, seeds at lower initial MC need more time to imbibe before the germination process can start. Seeds with higher initial MC were probably able to cope better with water deficit, at least during the 30-day germination test in the laboratory. A second experiment carried out on beechnuts treated only before storage but made to have different initial MC seemed to confirm this conclusion. Ungerminated seeds were not damaged, as revealed by a tetrazolium test performed at the end of each germination test. Advantages in nursery practice shown by dry, nondormant beechnuts (pretreated before storage) are discussed in relation to the possibility of sowing when water availability in the soil is not a limiting factor.