Responses of Thai recommended rice cultivars to high temperature in PSII efficiency at panicle initiation stage

Abstract

Photosynthesis is a major process for determining plant growth and development. The temperature plays important roles in plant photosynthesis. Thus, this research aimed to study the temperature response of PSII efficiency in different Thai recommended rice cultivars at panicle initiation (PI) stage. Youngest fully expanded leaves of fifteen rice cultivars namely, N22 (heat tolerance), IR64 (heat sensitive), CN1, Dular, PSL2, PTT1, Riceberry, RD29, RD31, RD41, RD49, RD57, RD61, RD63 and SPT1 at PI stage were exposed to temperature ranged from 25-55°C. During the exposure experiment to the temperature, coinciding measurements on the effective quantum yield of PSII efficiency (ΔF/Fm') and maximum quantum yield of PSII efficiency (Fv/Fm) were carried out. The experiment was designed in CRD with 4 replications. Temperature response to ΔF/Fm' and Fv/Fm showed a parabolic curve in all rice cultivars but Fv/Fm showed a wider parabolic curve than ΔF/Fm'. Optimum temperature of ΔF/Fm' and Fv/Fm was 31.83-35.64°C and 31.82-34.10°C, respectively. The ranges of supraoptimal temperature of ΔF/Fm' and Fv/Fm were 47.15-50.60°C and 46.93-48.65°C, respectively. On the other hand, the high temperature stress of ΔF/Fm' and Fv/Fm was 50.80-54.70°C and 50.93-52.50°C, respectively. Optimum temperature of ΔF/Fm' showed high correlation with supraoptimal temperature especially in cv. PTT1. Broad sense heritability of ΔF/Fm' under high temperature stress was the highest which could be used as selection criteria for heat tolerance in rice breeding programme.