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Abstract [Objectives]This study was conducted to investigate the control efficacy of 6% ascorbic acid water aqua on kiwifruit bacterial canker. [Methods] The ascorbic acid water aqua was sprayed onto annual potted kiwifruit seedlings once every 5 d， for three times in total， and Pseudomonas syringae pv. Actinidiae was inoculated by needle punching 7 d later. Scab diameter and number of newly infected scab were investigated to analyze the control efficacy. [Results] Kiwifruit plants were treated with 6% ascorbic acid water aqua， and after 30 d， the 20 mg/L treatment showed an incidence rate of 25.5%， and the 60 mg/L treatment exhibited an incidence rate only of 12.1%； and after 60 d， the relative control efficacy reached 90.7% at the mass concentration of 60 mg/L. [Conclusions] The 6% ascorbic acid water aqua weakened the destruction and expansion of the pathogen in plants， effectively improved the resistance in kiwifruit plants， and had certain control efficacy on kiwifruit canker.
Key words 6% ascorbic acid water aqua； Kiwifruit； Bacterial canker； Control； Research
Kiwifruit （Actinidia chinensis Planch） is a deciduous liana belonging to Actinidia in Actinidiaceae family. Its fruit contains rich nutrition， and has higher edible and medicinal value， and the extracts of root， stem and fruit of kiwifruit have anti-tumor effect. Kiwifruit is one of the three kinds of rising fruit in China， which is honored as "the Champion of Vc" and "The King of Fruit"[1-3]. In current cultivation， kiwifruit bacterial canker harms the production of kiwifruit to different degrees. It not only affects yield and quality， but also has caused the severe consequence of ruining the garden for multiple times in China. Kiwifruit bacterial canker seriously threatens kiwifruit production， and has been listed as the China Forestry Plant Quarantine Objects[4-6]. How to effectively control kiwifruit bacterial canker has become a research hotspot. The disease is mainly controlled chemically， while chemical control would cause agro-chemical residue and environment pollution， thereby threatening human health. With the enhancement of people’s health consciousness， green production and green food have been deeply rooted in the hearts of people. Therefore， in recent years， the biological control method improving disease resistance by inducing or activating resistant substances in agricultural crops with the characteristics of wide spectrum， lasting effect and high stability and safety has attracted more and more attention， and has been widely researched and applied in plant protection field[7-8]. 6% ascorbic acid water aqua is a kind of green environmentally-friendly multifunction biological bactericide produced by Guizhou Maofeng Plant Growth Promoter Factory. In production process， none of the three wastes is discharged， and in use， there are no environmental pollution and no residue. Acute oral and skin tests on rats shows that its LD50 is higher than 10 000 mg/kg. It has no irritation to eyes of rabbits， and the oral LD50， skin LD50 and inhalation LD50 are all higher than 5 000 mg/kg. Therefore， 6% ascorbic acid water aqua is a kind of slightly toxic agro-chemical. It is nearly suitable for all the agricultural crops， and for damage caused by natural disaster （such as low-temperature icing） or improper drug delivery， crops could recover rapidly after the application of the 6% ascorbic acid， which could be applied to agricultural crops safely at any growth stage， achieving very significant ecological benefit， social benefit and economic benefit. It is reported that ascorbic acid resists various stresses on the basis of antioxidation， and it achieves general resistance by scavenging a large number of reactive oxygen species， thereby promoting plant growth and development[9]. Secondly， 6% ascorbic acid water aqua could induce the increase of chlorophyll content in Rosa roxbunghii， effectively promote photosynthesis， and alleviate powdery mildew of R. roxbunghii. It also could induce R. roxbunghii plants to acquire systematic resistance. It also has a better induction effect on potato and cherry[10-12]. On this basis， a preliminary study on the control of kiwifruit bacterial canker by 6% ascorbic acid water aqua was conducted， so as to provide a scientific basis for field application.
Materials and Methods
Tested materials
Tested bacteria The tested bacteria were Pseudomonas syringae pv. Actinidiae.
Rested agent 6% ascorbic acid water aqua was produced by Guizhou Maofeng Plant Growth Promoter Factory.
Tested seedlings The tested variety was Hongyang， and the tested seedlings were potted seedlings of one year old.
Experimental method
Potted experiments were done with reference to Sheng[13]. Potted kiwifruit seedlings with uniform growth vigor of one year old were selected， and six treatments were designed in total. At first， 6% ascorbic acid water aqua were diluted to mass concentrations of 20， 40， 60， 80 and 100 mg/L， and clear water was used as control treatment. Each treatment included four replications. The spray treatment was carried out in late February， and each treatment was sprayed with corresponding solution once every 5 d， for three times in total. The suspension of the pathogenic bacteria was prepared and observed under a microscope 40×15 to have 50 bacteria in each view. The suspension of P. syringae pv. Actinidiae was inoculated on the kiwifruit seedlings with injectors 5 d after the last spraying by needle punching， followed by the step of keeping wet for 48 h. For each treatment， 60 positions were inoculated， and conventional management was performed after inoculation. The diameters of scabs were measured 30 d after inoculation， and the incidence rate and control efficacy were calculated. The expansion of old scabs was observed 60 d after inoculation， the number of new scabs was investigated， and relative control efficacy was also calculated. （1） Calculation formulas of disease index and control efficacy
Incidence rate= （Number of diseased positions/Total number of inoculated positions）×100%
Disease index=[∑（Number of branches or scabs of corresponding disease grade×Grade value）/（Total number of investigated branches or scabs×The highest grade）]×100
Control efficacy =[（Disease index of CK-Disease index of treatment）/Disease index of CK]×100%
Increasing rate of scab =[（Total number of scabs of later time-Total number of scabs of former time）/Total number of scabs of former time]×100%
Relative control efficacy=[（Expansion area of scale of the CK-Expansion area of scale of treatment）/Expansion area of scale of the CK]×100%
（2） grading standard of disease
Kiwifruit canker is divided into four grades[14]： grade 0， free of disease； grade 1.， slightly diseased， less than 1/3 of the branches are diseased or withered， or the scab of the main stem covers less than 1/3 of stem girth； grade 2， moderately disease， 1/3-1/2 of the branches are diseased or withered， or the scab of the main stem covers 1/3-1/2 of stem girth； grade 3， seriously diseased， 1/2-3/4 of the branches are diseased or withered， or the scab of the main stem covers 1/2-3/4 of stem girth； and grade 4， all the plant dies.
The experimental data were analyzed in Excel.
Results and Analysis
It could be seen from Table 1 and Table 2 that 6% ascorbic acid water aqua had a stronger protective effect on kiwifruit canker， with the concentration of the solution increasing， the control efficacy and relative control efficacy also increased， but when the mass concentration exceeded 60 mg/L， the control efficacy and relative control efficacy had no remarkable increase. As shown in Table 1， 30 d after the treatment， the incidence rates of plants decreased remarkably， and were all lower than 30%， and at the mass concentration of 20 mg/L， the control efficacy on the disease was also remarkable， and still could reach 60.5%. It was indicated that 6% ascorbic acid water aqua stimulated some defensive mechanism of plants， thereby reducing the rate of the pathogen invading plants. As shown in Table 2， 60 d after inoculation， compared with the CK， the plants treated with 6% ascorbic acid water aqua exhibited fewer new scabs， the increasing rate of scab was controlled below 30%， and the expansion rate of scab decreased remarkably， which was reflected by the highest expansion area within 30 d only of 5.13 cm2， while that of the CK was 28.56 cm2. The relative control efficacy was 82.0% at the mass concentration of 20 mg/L and about 91% when the concentration was in the range of 60-100 mg/L. It was indicated that 6% ascorbic acid water aqua improved the resistance of kiwifruit plants， weakened the destructive effect of the pathogen in plants and inhibited the expansion of P. syringae pv. Actinidiae in plants. Conclusions and Discussion
In recent years， kiwifruit has suffered from serious diseases and pests， as well as severe weather such as cold spell in later spring， in the main producing areas in Guizhou Province， and the yield and quality of kiwifruit have been affected seriously. Researches show that ascorbic acid mainly functions as cofactor of biological reaction， antioxidant for scavenging free radicals， and donor or receptor of electron transport chain in plasma membrane and chloroplast in plants， and thus affects many aspects of plant growth and development， playing a better role in resisting oxidation and adversity stress[9]. Researches also show that in plants， ascorbic acid content has remarkable correlation with oxidation resistance. Through the reduction of ascorbic acid content in plants， the sensitivity to various oxidation stress in plants is remarkably improved， the resistance against various biotic and abiotic stresses decreases remarkably， and the aging of plant is also accelerated[9，15]. However， when the ascorbic acid in plants is improved artificially， the resistance of plants to oxidation stress and other stresses is improved， tissue aging is also effectively delayed， various growth and development processes of plant are affected， and plant growth and development is effectively regulated[6，16]. Furthermore， ascorbic acid mainly functions as antioxidant for eliminating the damage of reactive oxygen species on tissue cells and cofactor of many enzymes participating in various vital activities related to resistance against oxidative stress in human and higher animals， such as viral or bacterial infection， tumor， cardiovascular disease， aging， et al.[6，17]. In this study， potted experiments about the control of kiwifruit bacterial canker by 6% ascorbic acid water aqua were carried out， and the results showed that 6% ascorbic acid water aqua had a stronger protective effect on kiwifruit canker， and with the increase of concentration of the bactericide， the control efficacy and relative control efficacy were also improved， but when the mass concentration exceeded 60 mg/L， the control efficacy and relative control efficacy were not improved significantly. Therefore， the mass concentration of 60 mg/L is advised in production， as a too-high concentration would cause waste and increase of production cost.
This study verifies that in production， ascorbic acid water aqua has certain regulatory and inductive effect on plant growth and development， and improves resistance in plant. Ascorbic acid is a substance necessary for plant growth， as well as a living substance necessary for human. It would not convert to substances toxic to human body after induction， and serves as an environmentally-friendly green disease prevention technique. Ascorbic acid is safe to kiwifruit growth as well as to human health. Therefore， in order to adapt to the green requirement for fruit quality at present， applying 6% ascorbic acid water aqua to improve plant resistance and enhance plant immunity might become one of the main content of the green prevention and control technical system of fruit tree diseases and pests， and will certainly become a new immunity and resistance induction technique in modern agriculture and modern plant protection， which would be applied more and more extensive[18]. References
[1] GONG HW. Causes of cold injury of Hongyang kiwifruit and discussion of control measures[J]. Shaanxi Journal of Agricultural Sciences， 2013， （5）： 134-135.
[2] Scientific Research and Education Department of Shaanxi Agricultural Bureau， Shaanxi Institute of Pomology. Kiwifruit[M]. Xi’an： Shaanxi science and technique publishing house， 1982.
[3] HUANG HW. Advance in kiwifruit[C]. Beijing： Science Press， 2000.
[4] SONG XB， ZHANG XW， MA ST， et al. Research status and prospect of kiwifruit canker[J]. Shaanxi Forest Science and Technology， 1997， 62-64.
[5] ZHU XX， FANG YZ， LIAO XG， et al. Study on kiwifruit canker pathogen[J]. Hunan Agricultural Sciences， 1993，（6）： 31-33
[6] CHENG HY， LI Y， ZHANG J， et al. Pathogenic identification of kiwifruit bacterial canker in Anhui[J]. Journal of Anhui Agricultural University，1995，22（3）： 219-233.
[7] YANG PY， ZHAO ZH. Manual of green prevention and control technology of agricultural crop diseases and pests[M]. Beijing： China Agriculture Press， 2012： 104-113.
[8] LI GJ， LID Y， SONG FM. Plant induced immunity and its application[J]. Acta Agriculturae Zhejiangensis， 2008， 20（1）： 72-77.
[9] HUANG M. Study on the molecular mechanism of Cili high content of ascorbic acid accumulation[D]. Wuhan： Huazhong Agricultural University， 2013.
[10] YAN K， LUO ZL， HU FL， et al. Ascorbic acid 6% AS inducing resistance against Sphaerotheca sp. in Rosa roxburghii Tratt[J]. Pesticides， 2017， 56（7）： 528-530.
[11] CHEN SX， XIA Z， HUANG RM， et al. Control effect of 6% ascorbic acid WA against potato late bright in Guizhou [J]. Guizhou Agricultural Sciences， 2014， 42（10）：135-137.
[12] WANG XD， ZHANG KK， WANG XL， et al. Yield-increasing effect of 6% ascorbic acid WA on three fruit varieties[J]. Guizhou Agricultural Sciences， 2014， 42（10）： 135-137.
[13] SHENG CB. Preliminary study on biological control of bacterial ulcer in Shaanxi[D]. Shaanxi： Northwest A&F University， 2006.
[14] MENG L. Effects of organic whole nutrient formula fertilization on the quality of Chinese fruit and the incidence of ulcer[D]. Shaanxi： Northwest A&F University， 2013.
[15] TALUKDAR D. Ascorbate deficient semi-dwarf asfL1 mutangt of Lathyrus sativus exhibits alterations in antioxidant defense[J]. Biologia Plantarum， 2012， 56（4）： 675-682.
[16] WANG P， YIN L H， LIANG D， et al. Delayed senescence of apple leaves by exogenous melatonin treatment： toward regulating the ascorbate-glutathione cycle[J]. Journol of Pineal Research， 2012， 53（1）： 11-20.
[17] HEMILA H. The effect of vitamin C on the common cold[J]. Journal of Pharmacy Practice， 2011， 24（2）： 241-242.
[18] LI P. Controlling crop disease using induced resistance： challenges for the future[J]. China Plant Protection， 2013， （10）： 82-85.
Key words 6% ascorbic acid water aqua； Kiwifruit； Bacterial canker； Control； Research
Kiwifruit （Actinidia chinensis Planch） is a deciduous liana belonging to Actinidia in Actinidiaceae family. Its fruit contains rich nutrition， and has higher edible and medicinal value， and the extracts of root， stem and fruit of kiwifruit have anti-tumor effect. Kiwifruit is one of the three kinds of rising fruit in China， which is honored as "the Champion of Vc" and "The King of Fruit"[1-3]. In current cultivation， kiwifruit bacterial canker harms the production of kiwifruit to different degrees. It not only affects yield and quality， but also has caused the severe consequence of ruining the garden for multiple times in China. Kiwifruit bacterial canker seriously threatens kiwifruit production， and has been listed as the China Forestry Plant Quarantine Objects[4-6]. How to effectively control kiwifruit bacterial canker has become a research hotspot. The disease is mainly controlled chemically， while chemical control would cause agro-chemical residue and environment pollution， thereby threatening human health. With the enhancement of people’s health consciousness， green production and green food have been deeply rooted in the hearts of people. Therefore， in recent years， the biological control method improving disease resistance by inducing or activating resistant substances in agricultural crops with the characteristics of wide spectrum， lasting effect and high stability and safety has attracted more and more attention， and has been widely researched and applied in plant protection field[7-8]. 6% ascorbic acid water aqua is a kind of green environmentally-friendly multifunction biological bactericide produced by Guizhou Maofeng Plant Growth Promoter Factory. In production process， none of the three wastes is discharged， and in use， there are no environmental pollution and no residue. Acute oral and skin tests on rats shows that its LD50 is higher than 10 000 mg/kg. It has no irritation to eyes of rabbits， and the oral LD50， skin LD50 and inhalation LD50 are all higher than 5 000 mg/kg. Therefore， 6% ascorbic acid water aqua is a kind of slightly toxic agro-chemical. It is nearly suitable for all the agricultural crops， and for damage caused by natural disaster （such as low-temperature icing） or improper drug delivery， crops could recover rapidly after the application of the 6% ascorbic acid， which could be applied to agricultural crops safely at any growth stage， achieving very significant ecological benefit， social benefit and economic benefit. It is reported that ascorbic acid resists various stresses on the basis of antioxidation， and it achieves general resistance by scavenging a large number of reactive oxygen species， thereby promoting plant growth and development[9]. Secondly， 6% ascorbic acid water aqua could induce the increase of chlorophyll content in Rosa roxbunghii， effectively promote photosynthesis， and alleviate powdery mildew of R. roxbunghii. It also could induce R. roxbunghii plants to acquire systematic resistance. It also has a better induction effect on potato and cherry[10-12]. On this basis， a preliminary study on the control of kiwifruit bacterial canker by 6% ascorbic acid water aqua was conducted， so as to provide a scientific basis for field application.
Materials and Methods
Tested materials
Tested bacteria The tested bacteria were Pseudomonas syringae pv. Actinidiae.
Rested agent 6% ascorbic acid water aqua was produced by Guizhou Maofeng Plant Growth Promoter Factory.
Tested seedlings The tested variety was Hongyang， and the tested seedlings were potted seedlings of one year old.
Experimental method
Potted experiments were done with reference to Sheng[13]. Potted kiwifruit seedlings with uniform growth vigor of one year old were selected， and six treatments were designed in total. At first， 6% ascorbic acid water aqua were diluted to mass concentrations of 20， 40， 60， 80 and 100 mg/L， and clear water was used as control treatment. Each treatment included four replications. The spray treatment was carried out in late February， and each treatment was sprayed with corresponding solution once every 5 d， for three times in total. The suspension of the pathogenic bacteria was prepared and observed under a microscope 40×15 to have 50 bacteria in each view. The suspension of P. syringae pv. Actinidiae was inoculated on the kiwifruit seedlings with injectors 5 d after the last spraying by needle punching， followed by the step of keeping wet for 48 h. For each treatment， 60 positions were inoculated， and conventional management was performed after inoculation. The diameters of scabs were measured 30 d after inoculation， and the incidence rate and control efficacy were calculated. The expansion of old scabs was observed 60 d after inoculation， the number of new scabs was investigated， and relative control efficacy was also calculated. （1） Calculation formulas of disease index and control efficacy
Incidence rate= （Number of diseased positions/Total number of inoculated positions）×100%
Disease index=[∑（Number of branches or scabs of corresponding disease grade×Grade value）/（Total number of investigated branches or scabs×The highest grade）]×100
Control efficacy =[（Disease index of CK-Disease index of treatment）/Disease index of CK]×100%
Increasing rate of scab =[（Total number of scabs of later time-Total number of scabs of former time）/Total number of scabs of former time]×100%
Relative control efficacy=[（Expansion area of scale of the CK-Expansion area of scale of treatment）/Expansion area of scale of the CK]×100%
（2） grading standard of disease
Kiwifruit canker is divided into four grades[14]： grade 0， free of disease； grade 1.， slightly diseased， less than 1/3 of the branches are diseased or withered， or the scab of the main stem covers less than 1/3 of stem girth； grade 2， moderately disease， 1/3-1/2 of the branches are diseased or withered， or the scab of the main stem covers 1/3-1/2 of stem girth； grade 3， seriously diseased， 1/2-3/4 of the branches are diseased or withered， or the scab of the main stem covers 1/2-3/4 of stem girth； and grade 4， all the plant dies.
The experimental data were analyzed in Excel.
Results and Analysis
It could be seen from Table 1 and Table 2 that 6% ascorbic acid water aqua had a stronger protective effect on kiwifruit canker， with the concentration of the solution increasing， the control efficacy and relative control efficacy also increased， but when the mass concentration exceeded 60 mg/L， the control efficacy and relative control efficacy had no remarkable increase. As shown in Table 1， 30 d after the treatment， the incidence rates of plants decreased remarkably， and were all lower than 30%， and at the mass concentration of 20 mg/L， the control efficacy on the disease was also remarkable， and still could reach 60.5%. It was indicated that 6% ascorbic acid water aqua stimulated some defensive mechanism of plants， thereby reducing the rate of the pathogen invading plants. As shown in Table 2， 60 d after inoculation， compared with the CK， the plants treated with 6% ascorbic acid water aqua exhibited fewer new scabs， the increasing rate of scab was controlled below 30%， and the expansion rate of scab decreased remarkably， which was reflected by the highest expansion area within 30 d only of 5.13 cm2， while that of the CK was 28.56 cm2. The relative control efficacy was 82.0% at the mass concentration of 20 mg/L and about 91% when the concentration was in the range of 60-100 mg/L. It was indicated that 6% ascorbic acid water aqua improved the resistance of kiwifruit plants， weakened the destructive effect of the pathogen in plants and inhibited the expansion of P. syringae pv. Actinidiae in plants. Conclusions and Discussion
In recent years， kiwifruit has suffered from serious diseases and pests， as well as severe weather such as cold spell in later spring， in the main producing areas in Guizhou Province， and the yield and quality of kiwifruit have been affected seriously. Researches show that ascorbic acid mainly functions as cofactor of biological reaction， antioxidant for scavenging free radicals， and donor or receptor of electron transport chain in plasma membrane and chloroplast in plants， and thus affects many aspects of plant growth and development， playing a better role in resisting oxidation and adversity stress[9]. Researches also show that in plants， ascorbic acid content has remarkable correlation with oxidation resistance. Through the reduction of ascorbic acid content in plants， the sensitivity to various oxidation stress in plants is remarkably improved， the resistance against various biotic and abiotic stresses decreases remarkably， and the aging of plant is also accelerated[9，15]. However， when the ascorbic acid in plants is improved artificially， the resistance of plants to oxidation stress and other stresses is improved， tissue aging is also effectively delayed， various growth and development processes of plant are affected， and plant growth and development is effectively regulated[6，16]. Furthermore， ascorbic acid mainly functions as antioxidant for eliminating the damage of reactive oxygen species on tissue cells and cofactor of many enzymes participating in various vital activities related to resistance against oxidative stress in human and higher animals， such as viral or bacterial infection， tumor， cardiovascular disease， aging， et al.[6，17]. In this study， potted experiments about the control of kiwifruit bacterial canker by 6% ascorbic acid water aqua were carried out， and the results showed that 6% ascorbic acid water aqua had a stronger protective effect on kiwifruit canker， and with the increase of concentration of the bactericide， the control efficacy and relative control efficacy were also improved， but when the mass concentration exceeded 60 mg/L， the control efficacy and relative control efficacy were not improved significantly. Therefore， the mass concentration of 60 mg/L is advised in production， as a too-high concentration would cause waste and increase of production cost.
This study verifies that in production， ascorbic acid water aqua has certain regulatory and inductive effect on plant growth and development， and improves resistance in plant. Ascorbic acid is a substance necessary for plant growth， as well as a living substance necessary for human. It would not convert to substances toxic to human body after induction， and serves as an environmentally-friendly green disease prevention technique. Ascorbic acid is safe to kiwifruit growth as well as to human health. Therefore， in order to adapt to the green requirement for fruit quality at present， applying 6% ascorbic acid water aqua to improve plant resistance and enhance plant immunity might become one of the main content of the green prevention and control technical system of fruit tree diseases and pests， and will certainly become a new immunity and resistance induction technique in modern agriculture and modern plant protection， which would be applied more and more extensive[18]. References
[1] GONG HW. Causes of cold injury of Hongyang kiwifruit and discussion of control measures[J]. Shaanxi Journal of Agricultural Sciences， 2013， （5）： 134-135.
[2] Scientific Research and Education Department of Shaanxi Agricultural Bureau， Shaanxi Institute of Pomology. Kiwifruit[M]. Xi’an： Shaanxi science and technique publishing house， 1982.
[3] HUANG HW. Advance in kiwifruit[C]. Beijing： Science Press， 2000.
[4] SONG XB， ZHANG XW， MA ST， et al. Research status and prospect of kiwifruit canker[J]. Shaanxi Forest Science and Technology， 1997， 62-64.
[5] ZHU XX， FANG YZ， LIAO XG， et al. Study on kiwifruit canker pathogen[J]. Hunan Agricultural Sciences， 1993，（6）： 31-33
[6] CHENG HY， LI Y， ZHANG J， et al. Pathogenic identification of kiwifruit bacterial canker in Anhui[J]. Journal of Anhui Agricultural University，1995，22（3）： 219-233.
[7] YANG PY， ZHAO ZH. Manual of green prevention and control technology of agricultural crop diseases and pests[M]. Beijing： China Agriculture Press， 2012： 104-113.
[8] LI GJ， LID Y， SONG FM. Plant induced immunity and its application[J]. Acta Agriculturae Zhejiangensis， 2008， 20（1）： 72-77.
[9] HUANG M. Study on the molecular mechanism of Cili high content of ascorbic acid accumulation[D]. Wuhan： Huazhong Agricultural University， 2013.
[10] YAN K， LUO ZL， HU FL， et al. Ascorbic acid 6% AS inducing resistance against Sphaerotheca sp. in Rosa roxburghii Tratt[J]. Pesticides， 2017， 56（7）： 528-530.
[11] CHEN SX， XIA Z， HUANG RM， et al. Control effect of 6% ascorbic acid WA against potato late bright in Guizhou [J]. Guizhou Agricultural Sciences， 2014， 42（10）：135-137.
[12] WANG XD， ZHANG KK， WANG XL， et al. Yield-increasing effect of 6% ascorbic acid WA on three fruit varieties[J]. Guizhou Agricultural Sciences， 2014， 42（10）： 135-137.
[13] SHENG CB. Preliminary study on biological control of bacterial ulcer in Shaanxi[D]. Shaanxi： Northwest A&F University， 2006.
[14] MENG L. Effects of organic whole nutrient formula fertilization on the quality of Chinese fruit and the incidence of ulcer[D]. Shaanxi： Northwest A&F University， 2013.
[15] TALUKDAR D. Ascorbate deficient semi-dwarf asfL1 mutangt of Lathyrus sativus exhibits alterations in antioxidant defense[J]. Biologia Plantarum， 2012， 56（4）： 675-682.
[16] WANG P， YIN L H， LIANG D， et al. Delayed senescence of apple leaves by exogenous melatonin treatment： toward regulating the ascorbate-glutathione cycle[J]. Journol of Pineal Research， 2012， 53（1）： 11-20.
[17] HEMILA H. The effect of vitamin C on the common cold[J]. Journal of Pharmacy Practice， 2011， 24（2）： 241-242.
[18] LI P. Controlling crop disease using induced resistance： challenges for the future[J]. China Plant Protection， 2013， （10）： 82-85.