Seed pre-soaking with brassinolide enhances the photosynthetic resistance of foxtail millet seedlings under mesosulfuron-methyl + iodosulfuron-methyl-sodium stress

Na Ning1, 2, Lei Huang1, 3, Binqiang Wang1, 4, Xiangyang Yuan1*, Pingyi Guo1
The mixture of mesosulfuron-methyl + iodosulfuron-methyl-sodium (ME+IMS) aspost-emergence dual-purpose herbicide exhibits phytotoxicity in foxtail millet (Setaria italica (L.) P. Beauv.) Reducing ME+IMS stress in foxtail millet is therefore of practical significance.This study assessed the effects of seed pre-soaking with different concentrations of brassinolide (0.01, 0.1, 1.0 and 2.0 mg L-1) on foxtail millet grown under ME+IMS (2.81+0.56 g ai ha-1) stress. The agronomic characteristics, photosynthetic pigment, gas exchange parameters, chlorophyll fluorescence and P700parameters of two foxtail millet cultivars ('Jingu 21' and 'Zhangza 5') were analyzed 7 d after ME+IMS treatment at the 5th leaf stage. Compared with ME+IMS treatment alone, brassinolide treatment within a concentration range of 0.1-1.0 mg L-1 had a positive effect on all plant parameters to varying degrees. Pre-soaking of seeds with 0.1mg L-1 brassinolide increased the leaf area (41.8%), fresh mass (179.2%), net photosynthetic rate (Pn, 38.4%), transpiration rate (Tr, 61.5%),stomatal conductance (gs, 103.1%), photosystem II maximum quantum yield (Fv/Fm, 8.6%), effective quantum yield(Y(II), 16.0%), electron transport rate (ETR(II), 17.8%), photosystem I photochemical quantum yield (Y(I), 16.7%) and electron transport rate (ETR(I), 38.7%) in 'Zhangza 5' leaves under ME+IMS stress. An increase in plant height (53.0%), total chlorophyll (38.3%), carotenoid contents (40.0%), and maximal P700 change (Pm, 34.3%) were also observed following 1.0 mg L-1 brassinolide treatment compared with ME+IMS in 'Jingu21'. Comprehensive analysis showed that pre-sowing seed treatment with 0.1-1.0 mg L-1 brassinolide could enhance the growth and photosynthetic resistance offoxtail millet seedlingsto ME+IMS stress.
Keywords: Brassinolide, photosynthetic physiology, seed presoaking, Setaria italica, sulfonylurea herbicide.
1Shanxi Agricultural University, College of Agronomy, Taigu 030801, China.
*Corresponding author (yuanxiangyang200@163.com).
2Chuxiong Normal University, College of Resources Environment and Chemistry, Chuxiong 675000, China.
3Tianjin Agricultural University, College of Agronomy and Resources Environment, Tianjin 300384, China.
4Jiangxi Institute of Red Soil, Jinxian 331700, China.