Abstract

The study was conducted using physiological approach to identify rice accessions with superior performance when subjected to infra-optimum temperatures during initial development phase (V₂-V₄). Forty-two rice genotypes composed by background essentially indica, japonica and indica/japonica cross with a broad genetic and ecological diversity were used. Plants were grown under initial optimum temperatures gradient (OTG - 22/32 °C night/day) until V2 stage; subsequently were subjected to infra-optimum temperature gradient (ITG - 13/17 °C night/day) during three days; after all genotypes returned to OTG conditions for seven days to recovery. Principal components analysis (PCA) highlighted that the three principal components account for 75.16% of total variation at the end of evaluated period. There were similar contributions of effective quantum yield (Y(II) - stress) and electron transport rate variables after recovery period (ETR - recovery) for PC1. Interestedly, genotypes highly responsive under initial OTG which showed fast initial biomass accumulation were also highly sensitive to stress when subjected to ITG, with accentuated decreases in their physiological performance. Sel. TB 1211-3 line, CTB 1419, CTB 1444, CTB 1455 and AB 13720 progenies showed greater performance for physiological analyzed variables, being potentially useful for breeding efforts aiming improve cold tolerance in rice at initial phase.

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