Methods to break seed dormancy in Cyclocarya paliurus (Batal)Iljinskaja

Dormancy in seeds of Dodonaea viscosa is due to a water-impermeable seed coat (physical dormancy, PY). Thus, mechanically scarified seeds imbibed water (c. 95% increase in mass) and germinated to high percentages over a wide range of temperature regimes in both white light and darkness, whereas non-scarified seeds did not take up water. Dry heat at 80‐160°C and dipping in boiling water for 1‐60 s also broke dormancy in a high percentage of the seeds, and continuous far-red light was not inhibitory to germination. However, dry storage in the laboratory for >1 year did not overcome dormancy. Seeds made water-permeable by boiling imbibed water, and thus germinated, at a much slower rate than those made water-permeable by mechanical scarification. We suggest that boiling opened the ‘water gap’ in the seed coat (not yet described in Sapindaceae but present in other taxa with PY) and that water entered the seed only through this small opening, thereby accounting for the slow rate of imbibition and subsequent germination. Physical dormancy has now been shown to occur in seeds of this polymorphic, worldwide species from Australia, Brazil, Hawaii, Mexico and New Zealand. The low level of dormancy reported for seed lots of D. viscosa in China, India and Pakistan is probably due to collection of seeds before they dried to the critical moisture content for development of water-impermeability of the seed coat. Germination of non-dormant seeds over a wide range of temperatures and in white light, far-red (leaf-canopy shade) light and darkness are part of the germination strategy of D. viscosa and of other taxa whose seeds have PY at maturity.

Physical dormancy in seeds of Dodonaea viscosa (Sapindales, Sapindaceae) from Hawaii

Occurrence of Physical Dormancy in Seeds of Australian Sapindaceae: A Survey of 14 Species in Nine Genera

Identification and characterization of the water gap in the physically dormant seeds of Dodonaea petiolaris: a first report for Sapindaceae.

Effect of Gibberellic Acid, Prechilling, Sulfuric Acid and Potassium Nitrate on Seed Germination and Dormancy of Annual Medics

In contrast to scarified seeds, unscarified seed did not germinate in any of the treatments, indicating that Koelreuteria paniculata Laxm. seeds have hard, impermeable seed coat dormancy. Exogenous application of 100, 200 and 300 ppm GA increased germination of scarified seeds from 0 (control) to 17, 18 and 15%, respectively. Pre-chilling in distilled water (DW) for 60 days increased germination to 44%. Compared with DW-chilled seeds, the germination of seeds chilled in gibberellic acid (GA-chilled) was significantly increased after 15 days of chilling and maximum germination of seeds chilled in 100, 200 and 300 ppm GA was 60, 51 and 54%, respectively, achieved after 30 days. Longer duration of chilling in GA appeared harmful. Germination rate was positively correlated with germination percentage. These results show that K. paniculata seeds exhibit both exogenous and endogenous dormancy. A combination of GA and chilling (GA-chilling) helped to alleviate seed dormancy in a relatively short period of time. # 2000 Elsevier Science B.V. All rights reserved.

S. Rehman

Papers

Short communication Effect of scarification, GA and chilling on the germination of goldenrain-tree (Koelreuteria paniculata Laxm.) seeds