A genome-wide association study using Myanmar diversity panel reveals a significant genomic region associated with heading date in rice.

Heading date is a key agronomic trait for adapting rice varieties to different growing areas and crop seasons. The genetic mechanism of heading date in Myanmar rice accessions was investigated using a genome-wide association study (GWAS) in a 250-variety diversity panel collected from different geographical regions. Using the days to heading data collected in 2019 and 2020, a major genomic region associated with the heading date, designated as MTA3, was found on chromosome 3. The linkage disequilibrium block of the MTA3 contained the coding sequence (CDS) of the phytochrome gene but not in its promoter region. Haplotype analysis of the 2-kb promoter and gene regions of revealed the six haplotypes, PHYCHapA, B, C, D, E, and F. The most prominent haplotypes, PHYCHapA and PHYCHapC, had different CDS and were associated with late heading and early heading phenotypes in MIDP, respectively. The difference in CDS effects between the PHYCHapB, which has identical CDS to PHYCHapA, and PHYCHapC was validated by QTL analysis using an F population. The distribution of PHYCHapA in the southern coastal and delta regions and of PHYCHapC in the northern highlands appears to ensure heading at the appropriate time in each area under the local day-length conditions in Myanmar. The natural variation in would be a major determinant of heading date in Myanmar accessions.