Impact of seed scarification, pretreatment with nitrogenous compounds and cold stratification on emergence percentage and growth of Gundelia tournefortii L. seedlings

The propagation of Gundelia tournefortii L. via seed faces certain problems due to the strongly lignified disseminule from secondary capitulum. Therefore, in this study, in first, the interaction of chemical and mechanical scarification (Control, sodium hypochlorite, H2O2, scalpel and sand paper for 10 min) with cold stratification (0, 1, 2, 3 weeks) or nitrogenous compounds (control, thiourea, nitrate, sodium nitroprusside) on seed dormancy breaking were investigated in two separate factorial experiments. Results showed that all scarification methods significantly increased emergence percentage and growth of seedlings and the interaction of scarification methods with stratification or nitrogenous compounds on these attributes was significant. In the first experiment, the highest emergence percentage (75.6 %) and length of seedlings (22.4 cm) was gathered in treatment of seed scarification by scalpel + 3 weeks cold stratification. In the second experiment, the maximum emergence percentage (65.6 %) and length of root (10.2 cm) and shoot (8.1 cm), and minimum mean time of emergence (11.5 days) of seedlings, was obtained in treatment of seed scarification by scalpel and applying sodium nitroprussid (SNP). In third experiment, the impact of combined application of SNP and cold stratification was assessed on dormancy breaking of seeds scarified with scalpel. Results showed that the application of SNP reduced duration of cold stratification required for obtaining the best emergence indices and maximum dry weight of seedlings. These results indicate that Gundelia tournefortii seeds have physical and physiological dormancy and can achieve the highest percentage of emergence (85%) and the lowest average emergence time (8.5 days) by treatments of scarification with scalpel and then cold stratification or SNP treatment.