Effects Of Growth Regulators On Main Physiological Characteristics And Yield Of Maize At Different Growth Stages Under Low Temperature Stress

In this study,potted plants of a single cross hybrid "Fumin 985" at seedling stage,large bellmouth stage,flowering stage and mid-filling stage were treated under low temperature stress in artificially settled climate chamber.And,the effects of three plant growth regulators of polydeterpenoid naphthalene(PKN),paclobutrazol(MET)and chlormequat(CCC)on the major physiological characteristics,dry matter weight and ear traits of maize.The results showed that(1)spraying plant growth regulators on maize leaves before low temperature treatments could effectively reduce Fv/F0,Fv/Fm and SPAD values of maize leaves as well as net photosynthetic rate(Pn),stomatal conductance(Cond),also reduce the activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT).Additionally,the content of malondialdehyde(MDA)in leaves and intercellular CO2 concentration in photosynthesis(Ci)were reduced.After the low temperature stress was relieved,the Fv/F0,Fv/Fm,SPAD,Pn and Cond values as well as the activities of SOD,CAT and POD of maize leaves sprayed PKN,MET and CCC were recovered faster than controls.Furthermore,the content of MDA in leaves and the concentration of Ci in photosynthesis decreased faster than the control.(2)Among the three growth regulators of PKN,MET and CCC,MET showed the most effectiveness on increasing CAT and POD activities and inhibiting MDA accumulation in maize leaves,and recovering the parameters of photosynthesis from low temperature stress.PKN had a better effect on increasing SOD and CAT activities,but could not effectively inhibit the accumulation of MDA in maize leaves.The effect of CCC on increasing the activities of SOD,CAT and POD enzymes was not better than MET and PKN,but the effect of CCC on inhibiting the content of MDA in maize leaves similar to MET was significantly better than PKN.(3)Under low temperature stress,PKN,MET and CCC showed divergent effects on ear traits of maize,but not significantly different on ear length,ear diameter,ear rows and ratio of kernels per ear.(4)Spraying PKN,MET and CCC at the seedling stage,large bellmouth stage and mid-filling stage was helpful to reduce the damage of low temterature on maize growth and development and increase ear weight,kernel weight per ear and hundred kernel weight,but the effects of different plant growth regulators sprayging at different growth stages were divergent.At the large bellmouth stage,the maize plants sprayed PKN harvested the highest ear kernel weight,whereas all the miaze plants sprayed CCC harvested the highest ear kernel weights at the seedling stage,flowering stage and mid-filling stage.