The phenotypic variation and genetic analysis of rice grain shape and weight under upland and paddy conditions

Rice is a globally important staple crop, and its growth and yield are significantly affected by climate change, particularly drought stress. Under water stress conditions, key agronomic traits such as grain shape (grain length, grain width, and length-to-width ratio) and grain weight may undergo significant changes, but their genetic basis remains incompletely understood. This study utilized a double haploid population derived from rice and upland rice varieties to investigate the phenotypic variation and genetic basis of grain shape and grain weight under both well-watered and drought-stress conditions. Phenotypic measurements and comparative analyses revealed that water stress significantly impacted grain shape and grain weight, with grain width being the most affected and grain length the least. Further QTL (quantitative trait locus) analysis identified 14 significant QTLs located on chromosomes 1, 5, 6, 7, 10, and 12, encompassing the genetic variation of grain length, grain width, grain weight, and length-to-width ratio. Key QTLs that exhibited stable performance under both upland and paddy conditions were identified, holding potential value for drought-resistant breeding. These stable QTLs can be employed in marker-assisted selection to accelerate the development of drought-tolerant rice varieties. The findings provide important insights into the phenotypic variation and genetic mechanisms of grain shape and grain weight under upland and paddy conditions, offering theoretical support and genetic resources for drought-resilient rice breeding.