EFFECTS OF REPETITIVE DRYING, ACID IMMERSION, AND RED-LIGHT TREATMENTS ON PHYTOCHROME- AND GIBBERELLIN-A3-MEDIATED GERMINATION OF SKOTODORMANT LETTUCE SEEDS

Ten-30 d imbibed skotodormant lettuce seeds (Lactuca sativa L. cv. Grand Rapids) showed no germination with water alone. However, following a single treatment of red light (R), gibberellin A3 (GA3) or 1 h acid immersion (pH 0.1) plus water rinse, 7% germinated. These imbibed skotodormant seeds germinated 85% or higher if acid immersion was carried out before R or GA3. Similar values were obtained with imbibed skotodormant seeds under acid immersion plus drying treatment applied at day 10 or 20 plus R or GA3 treatment applied 10 d later. One or two drying treatments alone reduced the degree of skotodormancy and made seeds more responsive to R but not GA3. Seeds with one R plus drying treatment at day 10 or 20 germinated about 50% with or without an additional R, and 80% or more with GA3 on day 20 or 30. The 20 or 30 d skotodormant seeds having R (with or without drying) or acid plus R and drying treatment on day 10 or 20 and additional dark incubation in water for 10 d showed 85 to 100% germination with only acid immersion. The skotodormancy was eliminated by the acid immersion but it was initiated again if R or GA3 treatment was not given immediately. It is concluded that the drying treatment, after elimination of skotodormancy by acid or acid + R pretreatment, prevents these seeds re-entering skotodormancy and maintains a high germination potential under dark storage for up to 20 d.