Effects Of Exogenous Methyl Jasmonate On Yield,Quality And Related Physiological Index Of Cotton Under High Temperature Stress

Cotton in the Yangtze River Basin often encounters high temperature stress during the flowering and bolling period,which leads to the decline of cotton pollen fertility,the shedding of young bolls and the increase of sterile seeds,which seriously affects the improvement of cotton yield.Methyl jasmonate（MeJA）,as a kind of plant growth regulator,can improve the stress resistance of plants under stress,but whether MeJA can improve the tolerance of cotton to high temperature stress and increase the yield under high temperature environment has not been reported.In this experiment,the line ZS08 bred in Hubei cotton area and the line ZT09 bred in Xinjiang inland cotton area were selected as the research objects.Under the artificial high temperature（3 days）environment and natural high temperature environment at the flowering and Bolling stage of cotton,different concentrations of MeJA（200,400 and 600μmol/L）were used to treat cotton plants,and compare the seed cotton yield,fiber quality,pollen vitality,photosynthetic characteristics,antioxidant enzyme activities and membrane lipid peroxidation between different treatments and controls,so as to provide technical support and theoretical basis for cotton high temperature and stress resistant cultivation technology.The main results are as follows:（1）Spraying MeJA can improve the total boll rate and average boll weight of cotton under natural high temperature stress,reduce the sterile seed rate,and reduce the negative impact of high temperature on cotton yield.Compared with CK,three concentrations of MeJA treatment significantly increased the total weight of ZS08seed cotton,The total weight of seed cotton under 200,400 and 600μmol/L treatment increased by 5.06%,9.70%and 12.50%respectively,showing a trend that the total weight of seed cotton increased with the increase of MeJA concentration.Compared with CK,only 400μmol/L treatment significantly increased the total weight of seed cotton of ZT09,200 and 600μmol/L treatment had no significant effect on the total weight of ZT09 seed cotton.（2）The appropriate concentration of MeJA can increase the length of cotton fiber flowering during natural high temperature stress.When the concentration of MeJA is too high,it will inhibit the elongation of cotton fiber length.Within the concentration range of this experiment,MeJA has no obvious effect on the uniformity,breaking ratio strength and micronaire value of cotton flowering during natural high temperature stress.Compared with CK,200μmol/L treatment had no significant effect on the fiber length of ZS08,400 and 600μmol/L treatment significantly increased the fiber length of ZS08.Compared with CK,200 and 400μmol/L treatment had no significant effect on the fiber length of ZT09 when the concentration increased to 600μmol/L,the fiber length of ZT09 was inhibited.（3）The results of short-term（3 days）artificial high temperature stress at the flowering and boll stage showed that the cotton young buds 7-9 days away from flowering of ZS08 were sensitive to high temperature.Spraying MeJA could better restore the pollen viability of the young buds at this stage.Compared with CK,the pollen viability at 7-9 days away from flowering under MeJA treatment increased by41.85%-90.89%.There was no significant difference in the effect of three MeJA concentrations on the improvement of pollen viability at this stage.（4）Under artificial high temperature stress,compared with CK,400 and 600μmol/L treatment significantly increased the net photosynthetic rate（Pn）,intercellular CO₂concentration（Ci）,transpiration rate（Tr）and stomatal conductance（Gs）of ZS08,effectively increased the accumulation of assimilates by increasing Pn,and decreased the leaf temperature by increasing Tr.Compared with CK,400 and 600μmol/L treatment significantly increased the activities of ZS08 superoxide dismutase（SOD）and peroxidase（POD）,significantly reduced the content of malondialdehyde（MDA）,improved the antioxidant capacity of leaves and enhanced the resistance of cotton to high temperature.The above results showed that spraying MeJA under high temperature stress at flowering and Bolling stage could improve the pollen vitality and high temperature resistance of cotton leaves,so as to improve the boll rate and boll weight,reduce the sterile seed rate and increase the yield of seed cotton.