The Resistance Effect And Mechanism Of SA And MeJA On Clubroot Of Chinese Cabbage

Chinese cabbage(Brassica rapa L.ssp.Pekinensis),belonging to Brassica crop of the Cruciferae family,is an important bluk vegetable crop originating from China.Recent years,Plasmodiophora brassicae Woron.can cause the roots swollen,aboveground wilting and the growth potential weak,which has occurred in 24 provinces(autonomous regions and municipalities)in China,and has become a major threat to the production of cruciferous vegetables crops in China.Under the basic national policy of adhering to ecological priority and promoting green development,chemical inducers have the advantages of broad-spectrum disease resistance,environmental friendliness,safety,uneasily to produce drug resistance,and long-lasting effects.So that,more and more scholars have paid attention to chemical inducers’ application in disease and other stress resistance of various crops.At present,few reports are about the disease resistance mechanism in Chinese cabbage after application of Me JA alone or the combination of SA and Me JA.Based on this,in this study,different concentration of Me JA and 500 μmol/L SA + different concentration of Me JA were used to treat clubroot-susceptible Chinese cabbage,to statistically analyze clubroot disease index,physiological and biochemical indexes,and defense genes of Chinese cabbage seedlings and revealed the induction and regulation mechanism of these two chemical inducers on Chinese cabbage clubroot.The main results are as follows:1.Taking the clubroot-susceptible Chinese cabbage cultivar "Jinguan" as the test material,under the stress of clubroot,exogenous treatment of more than 100 μmol/L(including 100 μmol/L)of Me JA can reduce the disease index and increase the chlorophyll content of Chinese cabbage seedlings.But with the increase of Me JA concentration,the biomass of Chinese cabbage seedlings significantly decreased.In addition,However,500μmol/L SA + Me JA with different concentrations can increase the biomass of Chinese cabbage seedlings and have a certain induction resistance,which is shown in: applying 500μmol/L SA+50-250 μmol/L Me JA could significantly reduce the disease index,and the induction effect was better than using 500 μmol/L SA alone,In 500 μmol/L SA+150 μmol/L Me JA treatment,the chlorophyll content of seedling leaves increased,and the effect was better than applying 500 μmol/L SA alone.2.Under the stress of clubroot,the comprehensive analysis of defense enzyme activity,soluble protein,and proline content in Chinese cabbage showed that the induction resistance effect was the best when the concentration of Me JA was 100μmol/L.In 500 μmol/L SA+10and 250 μmol/L Me JA treaments,the induced resistance effect was poor,and even lower than the control.When application of 500 μmol/L SA+50 or 150 μmol/L Me JA,the induced resistance effect was better than application of SA and Me JA alone.3.Under the stress of clubroot,exogenous Me JA significantly increased the content of JA in Chinese cabbage and decreased the content of SA,IAA,ZT and ABA.Exogenous500 μmol/L SA decreased JA content and increased SA content in Chinese cabbage,however,ABA,ZT and IAA content had no significant changes.After 500 μmol/L SA +Me JA reatment,the IAA content in Chinese cabbage decreased with the increase of the combined Me JA concentration.After 500 μmol/L SA+100 or 150 μmol/L Me JA treatment,the contents of SA,JA and ZT in Chinese cabbage were increased,and the content of ABA was decreased.By RT-q PCR,the expression of IAA synthesis-related genes PAP1 and Br CYP7PB2-1 further confirmed the effect of SA and Me JA on auxin in Chinese cabbage.4.After exogenous Me JA treatment,the relative expression of SA pathway gene PR-1and JA pathway genes PR-3,PDF1.2 and BCHI increased,thereby improving the stress resistance of Chinese cabbage,but it had a inhibitory effect on the expression of NPR1 gene;exogenous SA could increase the relative expression of gene NPR1 and SA pathway gene PR-1,and it had a short-term promoting effect on JA pathway genes PR-3,BCHI during 2hours,and then showed an inhibitory effect.To the relative expression of gene PDF1.2,exogenous SA showed an inhibitory effect.All these indicated that SA might inhibit the JA pathway,but Me JA had no obvious inhibitory effect on SA pathway and appeared synergistic effect.500 μmol/L SA + different concentrations of Me JA on SA,JA pathway gene expression in 50 μmol/L Me JA as the critical point.When mixed two chemical inducers,in treatments 500 μmol/L SA + low concentration of Me JA,the expression of SA pathway gene PR-1 was temporarily promoted and then inhibited,the JA pathway gene PR-3 was inhibited,and NPR1 was temporarily promoted.500 μmol/L SA + high concentration of Me JA could significantly promote the expression of gene PR-3 in JA pathway and inhibit the expression of gene PR-1 in SA pathway.The inhibitory effect on NPR1 weakened with time goes by.