Long-term elevated daytime temperature disrupts reproductive development and 2-AP biosynthesis gene expression in aromatic rice ‘KDML105’

Global warming poses a critical threat to rice production, with elevated daytime temperatures during reproduction causing irreversible yield losses. The premium aromatic cultivar ‘Khao Dawk Mali 105’ (‘KDML105’) is widely cultivated in Thailand but is highly heat-sensitive. To assess its vulnerability, plants were grown under controlled environments at 32, 36, and 40 °C from panicle initiation to maturity. Daytime warming ≥36 °C delayed flowering, shortened culm and panicle length, and inhibited uppermost internode elongation, resulting in incomplete panicle exsertion. Anther development was strongly affected, with reduced size, collapse of structural integrity, and poor pollen release at 36 °C, progressing to deformation and complete sterility at 40 °C. Spikelet fertility declined sharply with rising temperature, culminating in 100% sterility at 40 °C, confirming the narrow thermal threshold of ‘KDML105’. At the molecular level, elevated temperature downregulated proline–GABA pathway genes ( OsP5cs , OsProDH , OsOat , Osbadh2 ), suppressed biosynthesis of 2-acetyl-1-pyrroline (2AP), and increased volatilization losses, thereby diminishing aroma. Together, these results show that long-term elevated daytime temperature simultaneously compromises reproductive success and fragrance quality. Panicle traits and anther morphology serve as sensitive indicators for screening heat tolerance, while targeted breeding and adaptive agronomic strategies are essential to protect yield and grain quality in aromatic rice under future climate scenarios. • Daytime temperature ≥36 °C) during reproduction caused complete sterility in ‘KDML105’ rice. • High temperature reduced anther size, impaired dehiscence, and lowered pollen viability. • Culm elongation and panicle exsertion were suppressed, restricting pollination efficiency. • Elevated temperature downregulated proline–GABA pathway genes, limiting 2AP biosynthesis. • Long-term daytime warming threatens both yield and aroma quality in aromatic rice.