Research progress on identification methods and application of indica-japonica characteristics in Rice

Indica-japonica hybrid breeding is one of the effective approaches for increasing rice yield, accurately identifying the indica/japonica attributes of parental materials serves as the core foundation for efficient utilization of rice germplasm resources, exploiting inter-subspecific heterosis, and cultivating strong heterotic combinations. Over the past nearly 70 years, methods for identifying indica/japonica attributes have evolved from macroscopic morphological observation to microscopic genomic analysis. This paper describes the technical principles, advantages, limitations, and application status of several classification methods for determining indica/japonica attributes in rice. Among them, the Cheng's index method is the most typical classification approach, which is simple and intuitive, and is commonly used in field investigations, in molecular marker methods, SSR and InDel are the most frequently used markers, yielding more accurate and reliable results, based on whole-genome resequencing, high-throughput screening of SNP markers has enabled precise quantification of indica/japonica attributes.