Positive impact of paclobutrazol on gas exchange, chlorophyll fluorescence and yield parameters under submergence stress in rice

Abstract

Flooding is common in rainfed lowland areas of the world. Several physiological and biochemical plant processes were affected by the flooding, which causes deprivation of O2 in the root zone. Hence, a study was undertaken with four rice varieties, viz., Sita, IR64, FR-13A and Bharani, grown in simulated tanks and subjected to submergence stress. The effect of anti-GA compound paclobutrazol on the recovery of plants including gas exchange, chlorophyll fluorescence and grain yield parameters were measured after submergence stress. Net photosynthesis rate declined in plants subjected to stress at seedling stage. Varieties FR-13A and IR 64 recorded higher photosynthetic rate than Bharani and Sita. However, paclobutrazol application enhanced photosynthesis and transpiration rate in all the varieties after the imposition of stress. Chlorophyll fluorescence parameter, viz., maximum quantum yield of PSII (Fv/Fm) declined under stress at panicle initiation stage in all four varieties. The decline in yield of PSII was less in FR-13A, followed by Bharani and IR 64. Moreover, decline in panicle weight and grain weight was observed in all the varieties under submergence stress; however decline was less when the plants were treated with paclobutrazol. Higher photosynthetic rate coupled with lesser decline in yield of PSII with paclobutrazol application increased the tolerance of variety towards submergence stress. Hence, paclobutrazol application alleviated the negative effect of transient submergence stress by contributing to the recovery of plants and maintenance of yield in rice.