*3.2. Exploring Dysgenesis in S.* × *hainanensis*

#### 3.2.1. Pollen Germination Rate and Stigma Receptivity

Under natural conditions, the pollen germination rate and stigma receptivity of single *S.* × *hainanensis* flowers is usually consistent with time (Figure 2). The pollen germination rate was highest (100% or close to 100%) on the first and second day of flowering. The pollen germination rate declined greatly by the third day and was lowest (20%) by the fifth day. Stigma receptivity peaked on the day of flowering, and 100% of the pollinated flowers bore fruits. On the fifth day of flowering, the entire style withered and stigma receptivity (5%) was almost lost.

**Figure 2.** Variations in pollen germination rate and stigma receptivity with flower age in *S.* × *hainanensis.*

#### 3.2.2. Artificial Pollination Experiment

After bagging with castration (apomixia), the *S.* × *hainanensis* ovaries grew slightly larger around the 10th day, and then stopped changing. After one month, the ovaries withered and dropped. The fruit setting rate was 0 (Table 2). Under natural conditions, the fruiting rate of *S.* × *hainanensis* was 45%. The fruiting rate without bagging with castration was very low (17.5%). The fruiting rate (10%) under net isolation with castration was lower than that under natural pollination. However, under artificial pollination, the fruiting rate in all treatment conditions (42.5% to 62.5%) increased remarkably.


**Table 2.** Fruit setting rate and seed setting number under different pollination methods.

*3.3. Relationships among Seed Germination, Survival of Seedlings, and Environmental Factors*

#### 3.3.1. Seed Germination Rate at Different Fruit Dropping Times

The artificial control experiment for the seed germination rate of dropped fruits at different times indicated that all indices significantly increase with increasing fruit dropping times (Table 3). At the fruit dropping time of 5–10 d, the seed germination rate was 0, and the seed germination rate was less than 10% at 20–25 d. When the fruit dropping time was 30 d, the number of fruit falling (84.67%) and the seed germination rate (46.55%) reached the maximum. When the fruit drop time was 35 d, the fruit was no longer dropped. A chi square test showed that the seed germination rate was highly correlated with fruit dropping time (χ<sup>2</sup> = 63.29, *p* < 0.01).This indicates that under natural conditions, the early dropping of *S.* × *hainanensis* fruits leads to the incapacity of immature seeds to germinate, which could result in source limitation of seed.

**Table 3.** Fruit dropping amount and seed germination rate of *S.* × *hainanensis* at different fruit dropping times.


Different letters indicate significant difference (*p* < 0.05).

#### 3.3.2. Dynamic Observation and Verification of Seeds under Natural Conditions

It can be seen from Table 4 that under natural conditions, the fruit predation rate and seed germination rate at different distances are 100% and 0. The seed destruction rate (by animals and disease) and seed remaining rate were about 82.5% and 17.5%, respectively. Through field observations, it was found that crabs, squirrels, etc., were the main predators. In addition, the remaining seeds could not germinate. This indicates that the seed germination of *S.* × *hainanensis* under natural conditions is not only affected by animal predation, but also by habitat factors.


**Table 4.** Dynamic changes of fruit and seeds of *S.* × *hainanensis* under natural conditions.

3.3.3. Effects of Light Cycle Duration on *S.* × *hainanensis* Seed Sprouting

The seeds in the dark control group did not germinate. The germination rate, germination potential, radicle length, and radicle perfectness ratio were zero. Germination rate (Figure 3a), germination potential (Figure 3b), and radicle length (Figure 3c) demonstrated unimodal curves with increasing light cycle duration. Germination rate, germination potential, and radicle length differed under different light cycle durations (Figure 3). The germination rate (68.67%) and germination potential (58.67%) peaked at 12 h. The radicle length and radicle perfectness ratio did not statistically differ among different groups, except for the control group and the group at 4 h (Figure 3d).

**Figure 3.** Effects of different illumination times on indicators. Different letters indicate significant difference (*p* < 0.05).
