Effect Of Nitrogen Nutrition On Resistance Physiology In Downy Mildew Of Cucumber

The experiment adopts two cucumber varieties,which show different resistance against cucumber downy mildew,different levels of nitrogen of cucumber group under four nitrogen treatment.Select determination method which the laboratory technique of physiology biochemistry,determination of photosynthesis and the chlorophyll fluorescence technique unifies,under determination of different levels of nitrogen,invaded the change of cucumber adult plant's physiological biochemistry with the downy mildew,the response of three unions would be able more accurated and the rapid reflection of nitrogen nutrition coercion to the cucumber downy mildew morbidity process.The above work obtained the main results were shown as follows:1.The occurrence and progress of cucumber downy mildew was effected obviously by the nitrogen.It was advantageous in enhancing the resistance of the adult plant's downy mildew and,the reducing the condit -ion index.But high or low nitrogen conditions,especially under the 400kg.hm^-2 high nitrogen level condition, was more advantageous in infecting the occurrence of downy mildew,and enhancing the condition index of the adult plants;And the resistance of downy mildew of North China cucumber Jin qing10 hao was higher than the South China cucumber Ji li shi si.2.After the infection of cucumber downy mildew,the chlorophyll content and the soluble sugar content of disease leaves were loewr than healthy leaves,and under different nitrogen nutritional levels,the reduced extent of the chlorophyll and the soluble sugar content was least under the 240kg.hm^-2 nitrogen level,and their contents were both higher than other treatments.The disease plant's actives of PAL,POD and PPO were obviously higher than the healthy plant,along with the gradually increased of nitrogen nutrition,the enzymatic activitives were also gradually increased,when the nitrogen nutrition reached 240kg.hm^-2 level,the increased extent of the scope of enzymatic activtives were the biggest.But the scope of enzymatic activity reduced when the nitrogen nutrition continues increased to 400kg.hm^-2.The activitives of PPO and POD of Jin qing 10 hao increased higher than Ji Li shi si.The phenolics content and the nitrogen nutrition content had positive correlation,but along with the increasing of nitrogen nutrition,and reaching 400kg.hm^-2,the phenolics content was lower than 240kg.hm^-2 treatment.The phenolics content of every treatment was higher than healthy control,the accumulation of the phenolics content under nitrogen nutrition of 240kg.hm^-2 was higher than other nitrogen nutritive treatments,and the Jin qing 10 hao were obviously higher than Ji li shi si.3.Simultaneously discovered that the specific weght of leaf and total N concentration with photosynthesis ability appearanced statistical clear-cut correlation of two varieties of cucumber leaves, photosynthesis ability was not increased along with the increased of the specific weght of leaf and the total N concentration,the correlation curve was two parabolas.There were the correlation between the several levels of disease severity and the parameters of photosynthetic and chlorophyll fluorescence,and achieved the extremely significance level.Light saturation point and AQY of disease leaf was lower than the healthy adult plant,but the light compensation point was higher than the healthy adult plant.Under different nitrogen levels,the parameter of exchange gases Pn and Gs was reduced compared with healthy control plant after the infection of cucumber downy mildew,under the 240kg.hm^-2 nitrogen level,the descent extent of Pn and Gs was lower than other nitrogen treatments;The increased scope of Ci value was the smallest.After the infection of germs,under the 240kg.hm^-2 nitrogen level,the value of Pn and Gs of disease leaves were higher than other nitrogen levels.The change of Tr had no obvious regularity.The healthy adult plant of taking the clear water,under different nitrogen treatment,diurnal changes of net photosynthetic rate to assume the bimodal curve,the peak value presents 10:00 and 14:00.After infected by germs,various nitrogen nutritive treatments,compared with healthy contral that the value of net photosynthetic rate was reduced,diurnal changes of net photosynthetic rate was also assumed the bimodal curve,and the peak value was also appeared 10:00 and 14:00,but the 400kg.hm^-2 nitrogen level,the diurnal changes of net photosynthetic rate of disease leaf was presented the unimodal curve the form,the maximum appeared at 12:00 pm.After the infection of cucumber downy mildew,compared with the healthy control,the fluorescence value of Fo,Fm,Fv/Fo and Fv/Fm was reduced.Under different nitrogen treatment,the value of Fo,Fm,Fv/Fo and Fv/Fm under the 240kg.hm^-2 nitrogen level were higher than other treatments,and increased suitably nitrogenous fertilizer was possible to promote open degree of PSâ…¡of adult plant leaf,the value of FPSâ…¡, qp and ETR was higher than other nitrogen treatment,but the NPQ was actually lower than other treatments. After infected by germs,the value of FPSâ…¡,qp and ETR was dropped,but the NPQ was asvanced.Under the 240kg.hm^-2 nitrogen level,the drop scope of FPSâ…¡,qp and ETR was the smallest.Under the 400kg.hm^-2 high nitrogen level,the value of NPQ was increased the most.