Preliminary study on seed morphology and germination behavior in different development periods of Viola philippica

Viola philippica has two types of fruits: chasmogamous (CH) flowers and cleistogamous (CL) flowers. In addition, V. philippica has the characteristics of “sustained results” and “continuous seed dispersal”, and fruits of different maturity can be observed at the same time. Based on the observation of the fruit and seed morphology of V. philippica, the development process of the two types of fruits and the morphological germination characteristics of seeds at different development periods were compared. The results showed that: 1) The development time of CH fruit (24 ~ 29 days) was longer than that of CL fruit (16 days). 2) The CH and CL fruits had the same characteristics of development period and cracking dispersion. According to the angle between the fruit and fruit stalk and the morphological characteristics of the fruit, the maturity of the fruit (seed) is divided into 8 levels. With increasing development time, the length and width of CH and CL fruits and seeds showed an increasing trend, and the length and width of CH fruits and seeds were larger than those of CL fruits and seeds in each period. By contrast, the thousand-grain weight and water content of seeds were negatively correlated at different developmental stages; if the thousand-grain weight increased, the water content decreased. 3) When the angle between fruit and stalk was greater than 90° (after Ⅳ period), the thousand grain weight and water content of CH and CL seeds were fundamentally stable (about 1.00 ~ 1.15 g, 5% ~ 13%). The germination characteristics of the two seeds differed during different developmental periods. Under the condition of low maturity (before period IV), the germination rate, germination index, and vigor index of the two seeds were significantly increased (P < 0.05). After period Ⅳ, the germination indexes of seeds in each stage decreased after reaching their highest value, but the difference was not significant (P > 0.05). Thereafter, the germination percentage of seeds reached more than 80%, and the vigor index remained at a high level (400.00 ~ 550.00). In conclusion, an angle between fruit and stalk greater than 90° can be used as the standard for fruit harvesting, which is characterized by full CH and CL seeds, low water content, high germination percentage, and strong seed vigor.