Foliar spraying polyamine improving waterlogging resistance of summer maize in early grain filling stage

Abstract: Exogenous polyamine is a type of bioregulators and often used for drought resistance. This study investigated the feasibility to use it for waterlogging resistance in summer maize. A test-pit experiment was carried out in Shang qiu, China (24°35′N, 115°34′E, elevation 50.2 m). The waterlogging treatments for 3, 5, 7 and 9 days were designed in early grain filling stage of summer maize. At 3 days before ending waterlogging, the exogenous polyamine solutions or equivalent distilled water were sprayed 2 times per day (at 8:00 a.m. and 18:00 p.m.) to the maize in each treatment, respectively. Meanwhile, the field without waterlogging was set up as the control (CK). Samples were taken at 3, 6, 9 and 12 days after spraying for determination of soluble sugar content of leaves, root activity, shoot dry biomass, and endogenous spermidine content of leaves. At harvest, grain weight, yield and its components were measured. The results showed that: 1) After waterlogging in the early grain filling stage of summer maize, the soluble sugar content of leaves decreased. Spraying exogenous polyamine greatly increased the soluble sugar content. At 3 days after waterlogging, compared with distilled water treatment, the exogenous polyamine treatments for 3, 5, 7 and 9 days waterlogging significantly increased the soluble sugar content by 12.13%, 8.36%, 20.01%, and 12.17%, respectively (P<0.05); 2) At 3 days after waterlogging, compared with the distilled water treatments, the root activity for exogenous polyamine treatments in 3, 5, 7 and 9 days waterlogging was significantly increased by 24.76%, 40.45% and 31.46%, respectively (P<0.05). Overall, the root activity presented a upward-to-downward trend after the waterlogging; 3) The shoot dry biomass, spike length, rows per spike, kernels per row and yield of all the treatments were reduced significantly (P<0.05) compared to the CK. The spike core weight of 5 and 7 days of water flooding treatments decreased significantly (P<0.05), while there weren't significantly different at 3 and 9 days of water flooding treatment. The hundred-grain weight of 3, 7, and 9 days of water flooding treatment increased significantly (P<0.05), while dropped significantly after 5 days of waterlogging treatment. For the 3 and 5 days of waterlogging treatments, compared with treatments with distilled water, spraying exogenous polyamine increased the spike length by 6.56% and 7.80%, respectively, increased the rows per spike by 8.24% and 7.41%, respectively, and the increased the yield by 7.92% and 5.85%, respectively (P<0.05). In general, spraying exogenous polyamine was effective for waterlogging resistance in the early grain filling stage of summer maize when waterlogging lasted for 5 days or less, but the effect was not obvious for 7-9 days of waterlogging. In the future, different spraying amount and concentrations should be explored in order to find an optimal spraying amount and concentration. This study could provide useful information forthe recovery of summer maize after waterlogging.