Study On The Prevention And Control Of Sunburn And Its Physiological Mechanism By Orah Summer Shoot

In recent years,Orah has become the fastest develop citrus variety in Guangxi provincesince its attractive appearance,late maturity,high yield and good quality.According to the observation of our research group,in the south of Guangxi,the incidence rate of sunbu rn in orchard with serious disease,causing huge economic losses.In order to explore the control efficiency,environmental factors and physiological mechanism of the reserve summer shoots,In this study,we applied four-year old Orah as the experimental material and bearing brunches was dealt with according to different time and different numbers of reserve summer shoots,and the no reserve summer shoots was as control.By observing temperature,light intensity,incidence of sunburn,incidence of ulcers,fruit abscission rate,fruit quality,etc.,and comparing the best time and number of reserve summer shoots for controlling sunburn.By measuring the photosy nthesis,transpiration,mineral nutrients in the peel and leaves,the main enzyme activities of the peel,the structure of the sunburned peel,the soluble protein,the quality of the fruit,etc.of the optimal reserve summer shoots and the control treatment,and analysis correlation of various factors to clarify the inhibition of reserve summer shoots and its physiological mechanism.The main results are as follows:1.The results of different time and quantity of reserve summer shoots treatment show that the average temperature of the surface of the peel with different number of summer shoots is significantly different from 08:00 to 18:00 in the sunny days from July to September,and specific performance:1 reserve summer shoot>2 reser ve summer shoots>3 reserve summer shoots.From 10:00 to 14:00 on a clear day from July to September,the average light intensity of the peel treated with different number of summer shoots is significantly different,and specific performance:1 reserve summer shoot>2 reserve summer shoots>3 reserve summer shoots.In late J une,the photosynthetic transpiration rate decreases while the chlorophyll content increases of the treatment with 3 reserve summer shoots.2.The incidence of sunburn and the incidence index of sunburn susceptibility at different time and amounts of reserve summer shoots show extremely significant difference,and there is significant difference in fruit abscission rate between the treatments and controls.The incidence rate of sunburn,fruit abscission rate and sunburn susceptibility index of 3 reserve summer shoots are the lowest in late June,9.63%,11.83%and 5.96%respectively.The incidence of ulcer disease and the ulcer susceptibility index of different treatments of reserve summer shoots are significantly differed,3reserve summer shoots>2 reserve summer shoots>1 summer shoot.3.In late June,the soluble sugar,vitamin C,soluble solids and juice yield of 3 reserve summer shoots were the highest among all treatments.4.There is no significant difference in the weight of single fruit,titratable acid,vitamin C and soluble solids between sunburn fruit and normal fruit.The average peel thickness is 3.94 mm and 2.81 mm,the juice yield is 55.10%and 63.38%.5.The contents of K,Ca,Zn in the peel and leaves of 3 reserve summer shoots in late June are significantly different from those in the control.The contents K,Ca and Zn in the peel of the treatment groups are 13.55 mg/g,8.78 mg/g and 44.03%while those in the control are 10.78 mg/g,6.53 mg/g and 31.47%,respectively.The contents of K,Ca and Zn in leaves of the treatment groups are 13.06 mg/g,15.47 mg/g,26.48 mg/g,62.87%while those in the control are 14.57 mg/g,12.98 mg/g,23.71 mg/g,50.36%,respectively.6.The contents of Ca in the peel between the sprayed treatment and the control are significant difference,9.45 mg/gfor the treatment and 6.53 mg/g.The contents of Ca,Cu,Zn in the sprayed leaves and the control leaves show significant differrnce.The contents of Ca,Cu,Zn in the treatment are 26.58 mg/g,14.64%,59.15%,while those in the control groups are 23.71 mg/g,11.40%,50.36%respectively.7.The results show that after 3 reserve summer shoots in late June are infected by sunburn,the contents of O₂^-and MDA in the peels increased,the activities of CAT,POD and PPO increased.However,the activities of SOD,As A and GSH decreased.8.In late June,the contents of POD,SOD,CAT and soluble protein in the peel of 3 reserve summer shoots and sprayed treatme nts are higher than those of the control.9.The structure of yellow skin layer and white skin layer of the fruits infected by sunburn at first and second level are not damaged,a few of juice cells on the surface of the peel are gradually expanded.The structure of yellow skin layer and white skin layer of the fruits infected by sunburn at third and fourth level are damaged,and the juice cells on the surface of the peel are expanded and cracked,forming a gully and shrunk.The contents of soluble protein of one to four level are 5.14 mg/g,4.78 mg/g,3.57 mg/g and 2.95 mg/g.,respectively,which shows significant difference.According to the results of this study,the best way to prevent and control the sunburn is to leave 3 summer shoots in late June.After the sunburn,the structure of peel is destroyed and the conte nt of soluble protein decreased with the degree of sunburn increasing.The photosynthetic transpiration rate decreased and the content of chlorophyll increased.The contents of K,Ca,Zn and soluble protein in the leaves of summer shoots increased,and the activities of POD,SOD and CAT rose.It can provide more nutrition to the fruit,improve the ability of drought resistance,promote the synthesis and metabolism of protein,improve the enzyme activity of removing harmful substances in the body,enhance the ability of resisting external stress and inhibit sunburn.