Differential responses of middle-eastern rice genotypes to elevated nighttime temperature and ethylene inhibition

Abstract High nighttime temperature (HNT) is a rising threat to rice productivity and grain quality. Although the genotype responses to HNT stress have been widely investigated in Asian and U.S. rice germplasms, Middle Eastern rice genotypes remain largely unexplored despite their adaptation to warmer climates. This study evaluated the responses of 15 Iraqi rice ( Oryza sativa L.) genotypes, with or without 1-methylcyclopropene (1-MCP), to HNT stress. Plants were grown under greenhouse conditions and treated with ambient nighttime temperature (25 °C) or HNT (30 °C) from booting to maturity stage. Half of the plants, from both ambient and heat, received 1-MCP treatment prior to HNT exposure. Agronomic and grain quality traits were evaluated. Analysis of variance revealed significant genotype effects for all major traits. Significant genotype × 1-MCP interactions were observed for spikelet fertility and grain chalkiness. Nevertheless, biomass showed a significant genotype × heat × 1-MCP interaction. Correlation analysis showed grain yield was positively associated with spikelet fertility, biomass, and tiller number. Grain chalkiness showed weak negative relationships with yield-related traits. Cluster and ranking analyses grouped genotypes based on their responses to HNT conditions. ‘Amber33 type’ and ‘Amber type’ exhibited neutral to positive responses under HNT, whereas ‘Nema’ and ‘Shimla early’ were more sensitive. In several genotypes, 1-MCP treatment alleviated HNT-induced reductions in grain yield and spikelet fertility. Overall, this study provides an initial evaluation to elevated nighttime temperatures and ethylene response under HNT. The identified genotypes may be useful for future rice improvement efforts.