New Study Cracks The Code To Increasing Grain Size And Reducing Chalkiness In Rice

Rice is a staple food for millions of people around the world. Advances in genetics and breeding science have modernized rice cultivation, leading to improvements in grain weight, an important determinant of both grain yield and appearance quality in rice.

Studies focusing on quantitative trait loci (QTL)—small regions of DNA that control factors like grain size, length, and shape—have been at the forefront of these advances. By identifying favorable QTL (i.e., traits) and incorporating them into different rice varieties, scientists have been able to increase grain yield, contributing to greater food security. However, the potential of favorable QTL from wild rice varieties, which are not usually consumed, has been largely untapped.

A species of wild rice called Oryza glumaepatula has received some attention because it is an important source of genetic diversity for rice cultivar improvement. Therefore, a group of researchers from the South China Agricultural University and Guangdong Laboratory for Lingnan Modern Agriculture developed a series of germplasm resources by breeding O. glumaepatula with HJX74, an elite regular rice variety.

The study was largely divided into two phases. In the first part, several single-segment substitution lines (SSSLs) were generated using O. glumaepatula as the donor parent and HJX74 as the recipient parent. These SSSLs, in which foreign genes from O. glumaepatula were integrated into the genome of HJX74, were genetically analyzed, and 12 QTL that determine grain length (GL), 9 that determine grain width (GW), and 9 that determine kernel weight (TKW) were identified. Interestingly, some of these QTL were mapped to a novel "allele," i.e., a new genetic variant, called gl9.

This allele was a variant of the GS9 gene, a known regulator of grain shape and appearance quality in rice. Additional comparisons showed that the SSSL containing the gl9 allele had longer and more slender grains than the parent HJX74, and their TKW and grain yield per plant were also higher. This indicated that the gl9 allele was beneficial for improving rice quality.

Together, these findings imply the usefulness of gl9 as a target allele for improving rice production. Prof. Wang says that "in this era, it has become important for both farmers and governments to improve food production. Unfortunately, it is challenging to increase rice yield without compromising on its quality. Our findings regarding these new alleles such as gl9 that can improve both these factors are therefore of great importance."