Performance of Rice Genotypes under Low Temperature Stress during the Germination Phase

Rice (Oryza sativa) is a crop of significant social and economic importance, yet its productivity in Southern Brazil is frequently threatened by low temperatures, particularly during the germination stage. This study evaluated the germination performance of six economically relevant rice cultivars (SCS116 Satoru, SCS121 CL, SCS122 Miura, SCS124 Sardo, SCSBRS 126 Dueto, and BRS Querência) under cold stress. The experimental design involved testing 250 seeds per cultivar across five replications. Stress conditions were simulated by maintaining seeds in a Biochemical Oxygen Demand (BOD) incubator at 25°C for the first day, followed by six days at 15°C. Evaluation parameters included root length, leaf length, and a reduction index (RI) comparing total length under stress versus non-stress conditions. Statistical analysis (ANOVA, p < 0.05, and Scott-Knott test) revealed significant differences only for the RI, identifying two superior genotypes (SCS116 Satoru and SCS121 CL) with greater resilience to cold. These findings suggest that RI is a robust phenotypic marker for selecting early-stage vigor, which is critical for establishing uniform stands in temperate climates where thermal fluctuations are common. Furthermore, molecular analysis was conducted to identify the presence of the cold-tolerance gene Os03g0103300-qLTG3-1, a major Quantitative Trait Locus (QTL) known to accelerate germination under low temperatures by weakening the tissues covering the embryo. DNA sequencing of the 'Querência' (wild and mutant) and the study materials, performed via the Sanger dideoxy method following PCR amplification and fragment analysis using the BigDye Terminator v3.1 kit on a 3500 Genetic Analyzer and analyzed via MEGA 7.0 software, showed 100% similarity among them, indicating that these specific materials did not harbor the target tolerance gene. The absence of this allele in high-yielding cultivars underscores the need for introgressing diverse germplasm into local breeding programs. This genetic data provides a clear pathway for future hybridization efforts, suggesting that breeders must look beyond current high-performing lines to incorporate novel tolerance sources. Enhancing climate resilience through such targeted genetic strategies is vital for mitigating the impacts of erratic weather patterns, ensuring long-term sustainability and food security in rice agriculture across cold-prone regions. By integrating these phenotypic and molecular insights, agricultural programs can better develop cultivars specifically adapted to withstand the physiological challenges imposed by shifting global temperatures.