Effect of flower structure on the germination characteristics of Viola philippica

Viola philippica has a unique breeding system. In early spring, it can form chasmogamous (CH) flowers with flowering and fertilization, while in summer and autumn it can form cleistogamous (CL) flowers. The morphological and germination characteristics of CH and CL seeds were compared between these two morphologically different types of flower. The results showed that: 1) The length, width, and weight of CL seeds were significantly lower (P < 0.05). 2) Seeds from the two types of flowers began to germinate after 48 h of water absorption in greenhouse; however, initial germination was delayed by decreasing temperatures. When the thermoperiod was 10 ℃/20 ℃, but the time required for the germination rate of CL seeds to reach 50% was shorter than that of CH seeds. 3) The optimal germination temperature for the two types of seeds was 20 ℃/30 ℃ day/night, which triggered a germination rate above 95%. On the other hand, at 10 ℃/20 ℃ day/night, the germination rate and vitality index of CL seeds were significantly higher than those of CH seeds (P < 0.05). 4) The germination rate of CH seeds in a low-concentration NaCl solution (0.05～0.1 mol·L^–1) was lower than in a control solution (distilled water), while the germination rate of CL seeds was higher. However, the germination rate of the two types of seeds was lower after recovery by rehydration. 5) In a low-concentration NaCl solution (0.05 mol·L^–1), the vitality index of CL seeds was significantly higher than that of CH seeds. In conclusion, the breeding of V. philippica produces different CH and CL seeds through seasonal transformation, a phenomenon of great significance in mediating the reproduction and renewal of the population.