| Late blight seriously affects the yield and quality,which is one of the main restricting factors of potato production.Copper is one of the demanded microelements required for all the process of plant growth,development and reproduction.Also,it is the key components for copper based antibacterial compounds（CBACs）represented as the Bordeaux mixture,that make massive contributions in management of plant diseases during the past thirteen decades.Previously,we identified that copper ion acts as an elicitor and activates a series of defence responses to enhance the disease resistance in Arabidopsis by specifically regulating the expression of ACS8 and promoting the ethylene（ET）synthesis.In potato,copper ion inhibits the abscisic acid synthesis to trigger the defence response to Phytophthora infestans after activated the ethylene synthesis.We observed that the performance of disease management is better on fruit trees than on vegetables for the Bordeaux mixture.Combined the different application modes,we speculate that it may be related to the different leaves surface targeted by CBACs in different applications:the back sides of fruit trees leaves and the front sides of vegetables leaves have accepted more chemicals than their opposite sides of leaves.Therefore,we speculated that the performance of disease management of late blight will be different with the application of CBACs on back or front sides of leaves,caused by the different stomatal abundance between the front and back leaves.Aim to verify the speculation,we carried out our studies and achieved the following main results:（1）We validated that the stomatal abundance of back sides of epidermis was significantly higher than that of the front sides one in potato leaves.Under the condition setting in artificial climate chamber,the potato plants was presprayed with copper ion on the back or front,subsequently inoculated with P.infestans.The results showed that the back side application of copper ion have achieved better performance of disease control than the front side application.Consistent with the better performance than the front side application,the back side application of copper ion activated stronger series of defense responses,including with the accumulation of reactive oxygen species and the expression level of pathogenesis related genes.（2）Compared to the front side application,we have found that the stomatal aperture of the leaves have changed more rapidly and the stomatal conductance was larger at 3 h after spraying CuSO4 on the back side of leaves.The stomatal conductance was reached the peak value within2 h,and gradually recovered to a smaller value during the extension of time.（3）The accumulation of ethylene in potato leaves after copper ion treatment was determined by gas chromatography.We observed that the ethylene synthesis rate were higher for the leaves treated with back side of application than front side of application during 0.25 h to 0.75 h after spraying CuSO4.The biggest difference of the synthesis rate of ethylene was approximately 4.26 folds at 0.5 h between back and front side spraying of CuSO4.The expression of ET biosynthesis-related genes was detected by fluorescence quantitative RT-PCR.It was found that the back spraying mode stronger induced the related genes expression than the front spraying mode.（4）In the field pot experiments,the Kocide3000 contained the effective component of 46%cupric hydroxide was used as the standard agent to control potato late blight.The results showed that the back side of application is better performance to control the late blight than the front spraying mode,with the lower disease index.（5）A series of concentration gradient dilution tests were performed in the filed experiments too.It was found that the disease index of the potato plot is always lower in back side of application than that of front side of application with the same concentration of Kocide3000,The control effect was not affected by 1/3 reduction of Kocide3000 for using the back side of application.Overall,we proved that the back side of application CBACs promotes the performance of late blight management than the front side of application.And provided the evidence that we can reduce the amount CBACs by altering the application modes.Furthermore,our results indicated that there has a strong correlation between the copper ion-mediated plant immunity and stomatal abundance. |
