Paclobutrazol enhances lodging resistance and yield of direct-seeded rice by optimizing plant type and canopy light transmittance

Context or problem: Lodging is an important limiting factor for increasing yield and quality in direct-seeded rice (DSR) production. Optimizing crop plant types and the light environment within the canopy are crucial for improving lodging-related traits, and increasing yield. It is imperative to thoroughly investigate the correlation between basal internodes strength of DSR and canopy structure needs to be studied in depth. Objective or research question: The objectives of this study were to explore the mechanism of lodging resistance in DSR as affected by plant types and the light environment within the canopy, especially its related leaf traits changes and response to foliar application of paclobutrazol. Methods: In this study, a field experiment was conducted in Changchun, Jilin Province, China, by using two japonica rice varieties Jiyujing (JYJ) and Jijing305 (JJ305), with four different foliar application of paclobutrazol rates (0 mg L- 1, P0; 200 mg L- 1; P1; 300 mg L- 1; P2; 400 mg L- 1, P3) in 2021 and 2022. Results: Foliar application of paclobutrazol increased the grain yield of DSR by enhancing the chlorophyll content (SPAD) of the upper three leaves and net photosynthetic rate of the top leaves. Compared to the P0 treatment, the yield under the P1 treatment increased by 10.62 %-14.11 %. Principal component analysis revealed that lodging resistance of DSR was closely related to the photosynthetic performance of leaves and canopy light transmittance. Foliar application of paclobutrazol reduced the leaf angle of the upper three leaves of DSR, resulting in a more compact plant structure and improving light transmittance at the lower canopy levels, ultimately optimizing stem structure and internode quality. The increase of the SPAD value of the upper three leaves and net photosynthetic rate of the top leaves under paclobutrazol treatments also led to increased cellulose and lignin accumulation, enhancing the breaking strength of the basal internode and reducing lodging rate. Compared to the P0 treatment, the lodging rate of DSR decreased by 10.4 %-16.10 %. Conclusions and Implications: Foliar application of paclobutrazol improved the canopy light transmittance and leaf photosynthetic capacity by regulating leaf morphology and stem structure, reducing the lodging risk and ensuring the formation of DSR yield. Our results will assist breeders in breeding lodging-resistant and agronomists in improving field management practices for low lodging rate and high yield, and it will be illuminating for the resistance-lodging cultivation of DSR.