Starch granule size in grains of hybrid rice with low chalkiness occurrence

Abstract

Summary The occurrence of chalkiness has decreased in new hybrid rice cultivars in China. As both chalkiness occurrence and starch granule size are associated with the biosynthesis of starch, we hypothesized that there may be a correlation between chalkiness occurrence and starch granule size, and this may partially explain the decreased chalkiness occurrence in the new hybrid rice cultivars. To test this hypothesis, a field experiment was conducted over eight environments (two years × four sowing dates) with two hybrid rice cultivars: one recently developed with low chalkiness occurrence, Jingliangyou 1468 (JLY1468) and a relatively older cultivar with high chalkiness occurrence, Liangyoupeijiu (LYPJ). Results showed that JLY1468 had a higher cumulative distribution of large-diameter (7.51–19.50 μm) starch granules and a lower grain weight of milled rice compared to LYPJ. As a consequence, mean and relative starch granule diameters were 6% and 21% higher in JLY1468 than in LYPJ, respectively. Although both the chalky grain rate and chalkiness degree were negatively correlated with mean and relative starch granule diameter, they were more closely correlated with the relative granule diameter. These results support our hypothesis regarding the relationship between chalkiness occurrence and starch granule size and suggest that the relative starch granule diameter is a relevant parameter in understanding the occurrence of chalkiness in hybrid rice.

Relationship between Chalkiness and the Structural and Physicochemical Properties of Rice Starch at Different Nighttime Temperatures during the Early Grain-Filling Stage

“…Our results indicate that the CGR and CD were positively correlated with the proportions of volume (V) <10 µm, surface area (S) < 10 µm, and numbers (N) < 10 µm while the opposite, i.e., V >10 µm, S >10 µm, and N >10 µm, was observed under either the LNT or HNT. Cao et al [12] demonstrated that an increase in starch grain size helped to reduce the chalkiness of rice. HNT under the grain-filling stage led to a smaller diameter of the starch granules, which may have been related to increased α-amylase activity [48] and the inhibition of starch synthase [49].…”

“…An increase in the number of short chains in amylopectin, crystallinity, and the order of crystallinity, but a decrease in the number of long chains in amylopectin and the ratio of amorphous to ordered starch structure, leads to a deterioration in rice quality by enhancing its chalkiness [11]. In addition, the size distribution of the starch granules is also one of the critical factors affecting rice chalkiness [12]. In a study, scanning electronic microscopy (SEM) observation showed a deficient uniformity and regularity of starch granules, resulting in the altered transmission of light through the endosperm, thereby increasing the CGR and CD [13].…”