Performance of rice starch properties and eating quality value in recombinant inbred lines
The rice starch properties and EQ distributions of recombinant inbred lines (RILs) and their parents are shown in Fig. 1. The AC distribution range of RILs was 12.90–23.30%, with a mean of 17.60%; and the EQ distributed from 37.9 to 87.4, with a mean of 66.95. The corresponding distribution range and the mean for RVA profile characteristics was shown as below: PV, 1712–3727 RVU, 2745 RVU, TV, 1112–3235 RVU, 1723 RVU, FV, 1942–5308 RVU, 3040 RVU, BD, 191–2036, 952, CO, 580–2073, 1291, and SB 1242–1624, 292.5. Generally, the rice starch properties and EQ of RILs covered a wide range, and there was a super-parent distribution compared with the parent distribution.
Relationship between rice amylose content and RVA profile characteristics
The correlation between AC and TV, BD and SB, reached a very significant level of p < 0.01(Fig. 2) and the correlation with FV reached a significant level of p < 0.05. The TV, FV, CO and SB of the RVA profile characteristics were positively correlated with AC content, whereas PV and BD were negatively correlated with AC content.
Based on the mean AC content of 17.6%, the RILs were classified into two groups with high (n = 70) and low (n = 74) AC content. Differences in TV, FV, BD and SB performance were compared in different AC content groups (Fig. 3). The performance of TV, FV and SB in the high AC content group was significantly higher than that of the low AC content group, which was opposite to the BD performance; the low AC content group had a higher BD value.
Relationship between starch properties and eating quality in RILs
Figure 4 shows the correlation between starch properties and EQ values in the RILs. The AC content was negatively correlated with EQ value. Of the RVA profile characteristics, PV and BD were positively correlated with the EQ value, and the correlation between BD and EQ value reached a very significant level of p < 0.05. TV, FV, CO and SB were negatively correlated with EQ value, with a significance level of p < 0.01 for TV, FV and SB.
With EQ values of 60 and 70 as the limiting criteria, RILs were classified into high (EQ > 70, n = 48), medium (EQ: 60–70, n = 53) and low (EQ < 60, n = 43) EQ groups. The AC, TV, FV, BD and SB values that were significantly related to the EQ value were compared between the three EQ groups (Fig. 5). The high EQ group generally had a low AC, TV, FV and SB, but a high BD. The TV value was the best of the starch characteristics for distinguishing between the medium and low EQ groups.
Analysis of the assisted selection of eating quality of RILs by using starch properties
It appeared that the indicators AC, TV, FV, BD and SB were closely related to the EQ value obtained by sensory evaluation. Based on the assessment criteria of EQ, the 25th, 50th and 75th of the distribution of AC, TV, FV, BD and SB values were used as classification standards, and the five indicators were assigned with numeric values i.e., 20, 15, 10 and 5, respectively. The five indicator scores were added to derive a new indicator—viz., the starch properties quality (SPQ) (Fig. 6A)—which represented the comprehensive characteristics of rice starch that contributed to eating quality. The SPQ and EQ values were positively correlated at the significance level of p < 0.001(Fig. 6B).