Growth Rate, Dry Matter Accumulation, and Partitioning in Soybean (Glycine max L.) in Response to Defoliation under High-Rainfall Conditions

Muhammad Ali Raza; Hina Gul; Feng Yang; Mukhtar Ahmed; Wenyu Yang

doi:10.3390/plants10081497

Growth Rate, Dry Matter Accumulation, and Partitioning in Soybean (Glycine max L.) in Response to Defoliation under High-Rainfall Conditions

Plants (Basel). 2021 Jul 21;10(8):1497. doi: 10.3390/plants10081497.

Authors

Muhammad Ali Raza^{1

2

3

4}, Hina Gul⁵, Feng Yang¹, Mukhtar Ahmed⁶, Wenyu Yang¹

Affiliations

¹ College of Agronomy, Sichuan Agricultural University, Chengdu 611130, China.
² Sichuan Engineering Research Center for Crop Strip Intercropping System, Chengdu 611130, China.
³ Key Laboratory of Crop Ecophysiology and Farming System in Southwest China, Chengdu 611130, China.
⁴ National Research Center of Intercropping, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan.
⁵ University Institute of Biochemistry and Biotechnology, PMAS Arid Agriculture University, Rawalpindi 46300, Pakistan.
⁶ Department of Agronomy, PMAS Arid Agriculture University, Rawalpindi 46300, Pakistan.

Abstract

The frequency of heavy rains is increasing with climate change in regions that already have high annual rainfall (i.e., Sichuan, China). Crop response under such high-rainfall conditions is to increase dry matter investment in vegetative parts rather than reproductive parts. In the case of soybean, leaf redundancy prevails, which reduces the light transmittance and seed yield. However, moderate defoliation of soybean canopy could reduce leaf redundancy and improve soybean yield, especially under high-rainfall conditions. Therefore, the effects of three defoliation treatments (T₁, 15%; T₂, 30%; and T₃, 45% defoliation from the top of the soybean canopy; defoliation treatments were applied at the pod initiation stage of soybean) on the growth and yield parameters of soybean were evaluated through field experiments in the summer of 2017, 2018, and 2019. All results were compared with nondefoliated soybean plants (CK) under high-rainfall conditions. Compared with CK, treatment T₁ significantly (p < 0. 05) improved the light transmittance and photosynthetic rate of soybean. Consequently, the leaf greenness was enhanced by 22%, which delayed the leaf senescence by 13% at physiological maturity. Besides, compared to CK, soybean plants achieved the highest values of crop growth rate in T₁, which increased the total dry matter accumulation (by 6%) and its translocation to vegetative parts (by 4%) and reproductive parts (by 8%) at physiological maturity. This improved soybean growth and dry matter partitioning to reproductive parts in T₁ enhanced the pod number (by 23%, from 823.8 m^-2 in CK to 1012.7 m^-2 in T₁) and seed number (by 11%, from 1181.4 m^-2 in CK to 1311.7 m^-2 in T₁), whereas the heavy defoliation treatments considerably decreased all measured growth and yield parameters. On average, treatment T₁ increased soybean seed yield by 9% (from 2120.2 kg ha^-1 in CK to 2318.2 kg ha^-1 in T₁), while T₂ and T₃ decreased soybean seed yield by 19% and 33%, respectively, compared to CK. Overall, these findings indicate that the optimum defoliation, i.e., T₁ (15% defoliation), can decrease leaf redundancy and increase seed yield by reducing the adverse effects of mutual shading and increasing the dry matter translocation to reproductive parts than vegetative parts in soybean, especially under high-rainfall conditions. Future studies are needed to understand the internal signaling and the molecular mechanism controlling and regulating dry matter production and partitioning in soybean, especially from the pod initiation stage to the physiological maturity stage.

Keywords: crop management; defoliation; leaf area; photoassimilate.

Grants and funding

CARS-04-PS19/International Cooperation Project of Sichuan Province (2020YFH0126), and Program on Industrial Technology System of National Soybean (CARS-04-PS19).