Study On The Response And Effect Of Jasmonic Acid To The Infection Of V.nashicola

Pear scab is one of the most important diseases that restrict the development of pear industry,which brings huge loss to economic production.At present,chemical control is the main measure to control scab in pear production.The introduction of plant induced resistance provides a new idea for the control of plant diseases.The study on the main signal molecules and signal pathways of pear resistance to scab will help to understand the molecular mechanism of pear resistance,open up a new way of resistance breeding,improve pear resistance and control the prevalence of pear disease.Jasmonate is a new plant signal hormone.Whether it plays a role in the reaction of pear against scab,its mechanism and intensity of its action are still unclear.Therefore,the leaves of the susceptible variety ‘Xuehua’ pear and the resistant variety ‘Huangguan’ pear were used as the experimental materials.The role of jasmonate in signal transduction of different pear varieties was studied.And the possible relationship between jasmonate and Ca²⁺,NO signals has been explored.Moreover,the effect of exogenous application of Methyl Jasmonate on resistance of pear to scab was studied in order to find the way to improve resistance of pear to scab.The experimental results are as follows:The content of jasmonic acid in the leaves of ‘Huangguan’ pear was significantly higher than that of‘Xuehua’ pear when it was not inoculated with V.nashicola.The JA content of two varieties of pears increased after the infection of V.nashicola.The JA content of ‘Huangguan’ pear increased more rapidly,and the peak value was significantly higher than that of ‘Xuehua’ pear.MeJA had a direct inhibitory effect on the growth of V.nashicola.In the concentration range of 0.05² mmol·L^-1,the inhibitory effect of MeJA on the growth of V.nashicola increased with its concentration,and reached a significant level at the concentration of 0.1 mmol·L^-1.The results showed that JAs plays an important role in the interaction between pear and V.nashicola.And the strong resistant ‘Huangguan’ pear initiated JA signal earlier to participate in the disease resistance response and the response degree was higher.The expression of the key genes LOX,AOS,AOC and OPR3 in JA synthesis of the two varieties of pears were significantly induced by the infection of V.nashicola,and that of ‘Huangguan’ pear was more induced by V.nashicola and the gene expression level was higher.After Ca²⁺ and SNP treatment,the expression of JA synthesis related genes in ‘Xuehua’ and ‘Huangguan’ pear were increased to varying degrees.The AOC was activated earlier and the relative expression of OPR3 was significantly increased after two treatments.At the same time,both treatments induced the increase of JA content at different time points.Therefore,Ca²⁺ and NO may be involved in the regulation of pear resistance upstream of JA signal.The JA-dependent genes COI1,MYC2,and PR3 of ‘Xuehua’ pear and ‘Huangguan’ pear were all induced by the infection of V.nashicola.However,there were differences in expression time and relative expression between two different resistant varieties,and the increase in gene expression was more significant in the resistant variety ‘Huangguan’ pear.The JAZ genes of ‘Xuehua’ pear and ‘Huangguan’pear were also induced by the infection of V.nashicola,but the JAZ of ‘Huangguan’ pear decreased on the5 th day of inoculation,which promoted the activation of MYC2.The results showed that the resistant‘Huangguan’ pear had stronger JA signal transduction ability and might be involved in the regulation of resistance response of pear to scab.The leaf chlorophyll content of two varieties of pears was significantly reduced by the infection of V.nashicola.The chlorophyll content of ‘Huangguan’ pear decreased by 37% and ‘Xuehua’ by 49% at 9 day past infection.However,exogenous MeJA treatment could rapidly induce the expression of CAO in‘Huangguan’ pear and significantly increase the relative expression of CHLH and CAO genes in ‘Xuehua’pear at the later stage of infection（5-9 days）.It alleviated the decrease of chlorophyll content in leaves and maintained the normal photosynthesis,which played a positive role in the process of pear resistance.The production rate of superoxide anion and the content of H₂O₂ increased after the infection.However,the production rate of superoxide anion of ‘Huangguan’ pear was lower than that of ‘Xuehua’pear,and the content of H₂O₂ was higher than that of ‘Xuehua’ pear.At the same time,the activities of CAT,SOD,APX in ‘Huangguan’ pear were higher than that in ‘Xuehua’ pear.The results showed that‘Huangguan’ pear had stronger antioxidant system to enhance its resistance to scab.After MeJA treatment,the production rate of superoxide anion was reduced,the content of H₂O₂ was increased,and the treatment effect of ‘Xuehua’ pear was more obvious.At the same time,MeJA treatment significantly enhanced CAT,SOD,POD and APX activities and increased the expression of corresponding genes.The results showed that MeJA could increased the resistance of pear to scab by increasing the activity of protective enzyme.