*2.1. Di*ff*erences in Yield-Related Traits*

### 2.1.1. E ffect of P Fertilization in Low and High PA Rice

Yield-related traits of WRC 5 and WRC 6 are shown in Table 1. There were no significant di fferences in the panicle number and panicle weight between low and high PA plants. The panicle length of WRC 6 was significantly shorter than that of WRC 5. The panicle weight of WRC 5 was slightly higher than that of WRC 6. No significant di fference was observed in the total yield per plant.

**Table 1.** Yield-related traits in WRC 5 and WRC 6. Data are shown as the mean ± SD of 5–10 replicates. Data with asterisks indicate a significant di fference between WRC 5 and WRC 6 (Student's *t*-test, \*\*\**p* < 0.001).


2.1.2. Effect of the Amount of P Fertilizer on Initial Growth and Yield

To investigate the effect of P fertilizer on yield-related traits, the panicle weight and number (Table 2) and initial growth at the seedling stage (Table 3) were measured in WRC 5 and WRC 6. No significant differences were observed in WRC 5 and WRC 6.

**Table 2.** Panicle number and total yield per plant of WRC 5 and WRC 6. Data are shown as the mean ± SD of four replicates. Different letters indicate statistical differences (Tukey's HSD test, *p* < 0.05).


**Table 3.** Initial growth of WRC 5 and WRC 6 at the seedling stage. Data are shown as the mean ± SD of four to five replicates. ns indicates that there was no significant difference between WRC 5 and WRC 6 (Student's *t*-test).


### *2.2. E*ff*ects of the Time of P Fertilizer Application*

WRC 5 showed a lower PA content than WRC 6 under the control condition (Figure 1). When P fertilizer was applied at the seedling stage, WRC 5 presented increased PA content compared with that of the control, whereas WRC 6 presented no increase. When P fertilizer was applied in the heading stage, there was no significant difference in the PA content compared with that when P fertilizer was applied in the seedling stage.

**Figure 1.** Effect of the time of P fertilizer application on the PA content in WRC 5 and WRC 6. White, green, and orange indicate control, P applied in the seedling stage, and P applied in the heading stage, respectively. Each value represents the mean ± SD of four replicates. Different letters indicate statistical differences (Tukey's HSD test, *p* < 0.05).

### *2.3. Variation in the PA Content with Change in the P Concentration in the Soil*

To examine the effect of the amount of P fertilizer on PA accumulation in the grain, we applied different amounts of P fertilizer at the seedling stage and measured the PA concentration and content in harvested grains (Figure 2). In the control, WRC 6 showed a higher PA concentration and content than WRC 5 as expected (Figure 2a,b). We observed that the PA concentration and content in both cultivars increased under P4 treatment.

**Figure 2.** Effect of the amount of P fertilizer on PA accumulation in WRC 5 and WRC 6. (**a**) PA concentration per gram dry weight (mg/gDW), (**b**) PA content per grain (μg/grain), (**c**) PA content per plant (mg/plant). White, pale pink, and pink indicate control, P1 treatment, and P4 treatment, respectively. Each value represents the mean ± SD of four replicates. Different letters indicate statistical differences (Tukey's HSD test, *p* < 0.05).
