Storability and Treatments to Overcome Dormancy of Sweetheart Tree (Euscaphis japonica (Thunb.) Kanitz) Seeds

The objectives of this study were to determine effective dormancy-breaking treatments and to investigate the storage behavior of seeds of the sweetheart tree (Euscaphis japonica). The germination percentages of freshly collected mature seeds of sweetheart tree from Yangmingshan, Taipei (25°10’N, 121°33’E; elevation, 420 m) in 1999 were 0.3 and 26.8% under alternating temperatures 30/20℃ with 8 h of light and 35/10℃ with 8 h of light, respectively, for 20 wk. Most of the ungerminated seeds remained dormant after a 20-wk incubation. After a combined 3-mo warm and 2-mo cold stratification, the true initial germination percentage of this seedlot was 92.1 ± 4.2%. The following treatments were also found to be ineffective: 4℃ chilling alone, mechanical scarification, chemical scarification (pre-soaking in 25% H2O2, or pre-soaking in 98% sulfuric acid), 15 h of pre-soaking in 2000 ppm GA3, and soaking in GA3 for 15 h after mechanical scarification. Significant increases in seed germination (49.3~71.3%) were obtained after chilling at 4℃ for 3~5 mo and incubating under alternating temperatures of 30/20℃, whereas all seeds deteriorated when chilling was extended to 8 mo. Therefore, cold, wet conditions for a short-term storage are not recommended for sweetheart tree seeds. The dormancy of sweetheart tree seeds, however, can effectively be broken by a combination of warm stratification at 30/20℃ for 3 mo followed by cold stratification at 4℃ for 2 mo. Freshly mature seeds that were dried to moisture contents of 4.2 ± 0.4, 5.8 ± 0.4, 8.6 ± 0.3, 10.9 ± 0.5, and 17.2 ± 1.4% (on a fresh-weight basis) and treated with the combined stratification had germination percentages of 89.5 ± 4.3, 92.0 ± 2.0, 89.5 ± 4.3, 93.5 ± 3.0, and 96.0 ± 2.4%, respectively. Seed germinability could be maintained at -20, 4, and 15℃, for at least 24 mo at moisture contents of 4.2~10.9%, therefore, confirming the orthodox seed storage behavior of sweetheart tree seeds.