Effect of environmental factors on seed germination and seedling emergence of Viola prionantha, a cleistogamous plant

Environmental conditions during seed development and maturation can affect seed traits and germination behavior, yet systematic research on the effects of seed maturation time on seed traits, germination behavior and seedling emergence of cleistogamy plants is lacking. Here, we determined the difference in phenotypic characteristics of CH and CL (namely CL1, CL2 and CL3 based on maturation time, respectively) fruits/seeds that were collected from Viola prionantha Bunge, a cleistogamous perennial plant, and evaluated the effects of various environmental factors on seed germination and seedling emergence. The fruit mass, width, seed number per fruit and mean seed mass of CL1 and CL3 were greater than that of CH and CL2, while seed setting of CH was lower than that of CL1, CL2 and CL3. Germination of CH, CL1, CL2, and CL3 seeds was < 10% in the dark at 15/5 and 20/10 ℃, whereas germination (0%–99.2%) of CH, CL1, CL2, and CL3 seeds changed significantly under light conditions. In contrast, more than 71% (from 71.7 to 94.2%) germination of both CH, CL1, CL2 and CL3 seeds occurred under both light/dark conditions and continuous darkness at 30/20 ℃. Germination of CH, CL1, CL2 and CL3 seeds was sensitive to osmotic potential, but CL1 seeds were more resistant to osmotic stress, compared with CH, CL2 and CL3. Seedling emergence of CH seeds was more than 67% (from 67.8 to 73.3%) at a burial depth of 0 cm–2 cm, while all types of CL seeds were below 15% at a burial depth of 2 cm. Information gathered from this study indicates that CH and CL seeds of V. prionantha were different in fruit size, seed mass, thermoperiod and photoperiod sensitivity, osmotic potential tolerance and seedling emergence, especially, maturation time significantly affect phenotypic characteristics and germination behavior of CL seeds matured at different periods. These results indicate that V. prionantha adapts to unpredictable environmental conditions by developing a variety of adaptation strategies, and ensures the survival and reproduction of the populations.