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Abstract Survey was conducted to investigate the occurrence laws of bacterial canker disease of kiwifruits in Liupanshui area， Guizhou Province， and the pathogens and hazard symptoms of the canker disease were introduced. The results showed that the factors influencing the occurrence of bacterial canker disease of kiwifruit were identified as interspecies resistance， agronomic traits， meteorological and ecological conditions， cultivation and management techniques and fertilization levels. Techniques for the comprehensive control of kiwi canker disease were stated， and control suggestions were proposed.
Key words Bacterial canker disease of kiwifruit； Occurrence； Influencing factors； Control
Received： November 25， 2017 Accepted： January 25， 2018
Supported by the Fund Project for the Growth of Young Scientific Talents of the Department of Education of Guizhou Province （Qianjiaoguhe KY[2016]No. 269）； the Openend Fund for the Key Laboratory of Green Pesticide and Agricultural Bioengineering of the Ministry of Education， Guizhou University （2016GDGP0101）； the Projects for Undergraduates of Liupanshui Teachers Normal University （LPSSYDXS1613）.
Kai YAN （1981-）， male， P. R. China， master， agronomist， devoted to research about plant protection， Email： pxyankai@126.com.
*Corresponding author. Email： lk81@163.com
Since the discovery in Japan in 1980[1]， bacterial canker disease of kiwifruit has occurred in the kiwifruit producing areas all over the world. Widespread， pathogenic， difficult to eradicate and spreading rapidly， the disease is one of the most dangerous diseases for kiwifruit， leading to the great production reduction， high mortality rate of fruit trees. Some orchards even have been destroyed， resulting in great economic losses. It is a kind of world devastating bacterial diseases， which is threatening the development of world kiwifruit industry[2].
The pathogen of kiwifruit canker in Chinas kiwifruit producing area is mainly Pseudomonas syringae pv. actinidae （Psa）[3]. In recent years， with the adjustment of agricultural structure in Guizhou， the kiwifruit industry has got the continuous development with the continuous increase of planting area. On the other hand， the occurrence and harm of the bacterial canker kiwifruit disease in kiwifruit are becoming more and more common and serious. After the occurrence of kiwifruit disease， the yield is reduced with pericarp becoming thicker， taste sourer， fruit colar poorer， and so the fruit quality also declines[4]. Therefore， survey was conducted to investigate the occurrence laws of bacterial canker disease of kiwifruits in Liupanshui area， Guizhou Province， and the comprehensive control measures were put forward in order to provide reference for the effective control of the disease， so as to promote the healthy development of the kiwifruit industry in Guizhou Province. Occurrence and Symptoms of Bacterial Canker Disease of Kiwifruit
Pathogenic bacteria tend to invade the host body before and after flower bud formation from the stem shoots， fallen leaves scars， lenticels， and branches of the plants， mainly lurking over the winter in the diseased plants. The early spring （from late February to early March） is the period with the appropriate temperature for the activities of the pathogenic bacteria， when the harm of the bacteria begins. The pathogenic bacteria can endanger the trunk， branches， vines， leaves and buds and other parts of plants， and the pathogen damage peak appears before or after the bleeding exudation. Then， the pathogenic bacteria stop the activity with temperature rise and go through the summer and winter in the hosts， becoming the source of initial infection of the following year to continue the damage[5]. The bacteria can be transmitted by means of wind and rain， insects， manmade pruning， and can form multiple reinfection from the bacteria ooze from the affected parts of plants[6]. After infection， stems and branches of diseased plants show cortical water stains at the beginning， the tissues became soft and necrotic， gradually separated from the xylem， and then cracked. When the climate became humid， they produced milky white bacterial liquid， which turns brown or rusty after bleeding exudation[7]. Scabs can rapidly expand around the stem， the pathogen can invade the xylem， and after stripping the diseased cortex， the scab xylem is black， phloem ulcer rots， resulting in difficulty in transporting and absorbing the nutrients for the trees， weak tree bodies， even death in severe cases； The infected vines are watery and dark green. After infected， the upper cotyledons become curly， the leaf margins are scorched， and then the vines or shoots die after the enlargement of the scabs. Late spring and early summer and late autumn and early winter are the peak season for the occurrence in leaves. The newly born leaves first form watery greenish dots on the leaves after infection， sometimes red dots， which then develop into irregular polygonal brown or dark brown scabs with yellow rings of 2-5 mm. The scabs can expand rapidly under the conditions of continuous low temperature and humidity， making the leaf margin scorched， leaves curled. Sometimes there is no yellow rings， but atherosclerotic pathogens can be seen oozed from the back of leaves. From late April to mid May， buds generally cannot open after infection， and for those with light infection which can have flowers open， even they can grow into fruits， the fruits are small， which can be easy to fall off or become deformed fruits. Most of the infected buds turn brown and fall off[8]. For the kiwifruit fruits which are acupunctured to inoculate the pathogens， the pathogens do not expand into scabs， and only slightly become brown at the inoculation site. Factors Affecting the Occurrence of Bacterial Canker Disease of Kiwifruit
Relationship with climatic conditions
According to the survey results， the occurrence of kiwifruit canker disease was closely related to climatic conditions such as temperature， frost and altitude in the planting area. The climatic conditions of low temperature and high humidity were conducive to the occurrence and prevalence of kiwifruit canker disease. The longer duration of frostfree period， the less incidence of the disease， and the shorter duration of frostfree period， the more serious the disease. In the meantime， the higher the altitude， the more severe the disease. The survey found that in the same plantation， there was no incidence in the valley at the minimum altitude of 1 200 m， and the incidence rate was 18.5% at the highest altitude of 1 500 m. In the mountainous area of Guizhou， the temperature decreased with the increase of altitude， the humidity was great in spring and winter because of fog， and the frostfree period was short， making the plants vulnerable to cold damage， thereby resulting in serious incidence. The results were consistent with the findings of Wang， Li and others[4-6].
Relationship with kiwifruit varieties
It has found that there are differences in the resistance to canker disease between different kiwifruit varieties. The survey found that the general trend in cultivars in this region was that Hongyang had the most serious attack， and Guizhang： was the most resistant to disease. In the meantime， the wild plants and the seedlings were generally more resistant to the canker disease， and for the same variety， the one with wild kiwifruit as stock had higher resistance to the disease， which was consistent with the results of Li[9].
Relationship with the age of kiwifruit
The survey results showed that the incidence of trees of different age groups was different. In the affected planting area， there was no canker occurrence for the young trees of 1-3 years old. However， with the increase of tree ages， the fruit bearing amount increased， and the incidence rate and damage degree of canker disease also became more serious. The infection was more serious in the old planting area than the new one. The reason might be that with the increase of tree ages， the nutrition consumption for the kiwi tress became more after the fruiting entered the full bearing stage， then the tree vigor became weak， disease resistance declined， and combined with the accumulation of pathogens， it was conducive to the occurrence of disease. The incidence rate was low for young trees， and the damage degree was light， because the young trees mainly proceeded with the accumulation of nutrients in trees， and the plants could grow well， thereby showing strong disease resistance[6]. Relationship with the bearing amount of kiwifruit
According to the survey， for the orchards with the trees of the same age under the same management level， the one conducted with artificial pollination had high fruiting rate， almost no deformed fruits， yield reaching 36 000 kg/hm2， and weak tree growth vigor， while the other proceeded with natural pollination because of the shortage of manpower had more deformed fruits which were picked in the early period， low fruiting rate， yield of only 8 250 kg/hm2， and strong tree growth vigor. In the following year， the extreme climate led to the outbreak of canker disease， the incidence rate of the plot with high fruiting rate and yield reached up to 13.7%， while the plot with low fruiting rate and yield only had the incidence rate of 2.4%. The reason was that the large fruit bearing amount overconsumed the nutrients from the trees， resulting in plant nutrition disorders， disease resistance reduction， further leading to serious occurrence， which was consistent with the results of Zhang et al.[10]， Feng et al.[11] and Jin et al.[12]. At the same time， overuse of fruitexpander by fruit growers overburdened the fruit bearing amounts of fruit trees， which could also cause excessive consumption of nutrients and weaken the growth vigor of trees， making the trees more susceptible to canker disease. Delayed harvesting overconsumed tree nutrition and shortened the key period for the trees to store effective nutrients， resulting in poor plant resistance， declined tree vigor， thereby increasing the risk for the trees to infect canker disease.
Relationship with the seedling sources of kiwifruit
The survey found that in the same plantation， for the 6yearold seedlings under the same management conditions， the incidence of seedlings imported from Sichuan was 58.2%， showing severe incidence； there was no occurrence of canker disease for the local nursery seedlings for the first year， and the incidence in the following year was only 4.7%， which showed low index of decease infection and relatively late tree age for the incidence. The reason was that Sichuan was the place with early onset of kiwifruit canker disease， belonging to the epidemic area； the longdistance transportation resulted in water loss of some seedlings， which required a long time to regain the growth， so the nutrients could not be effectively accumulated in trees， which was not favorable for the improvement of disease resistance. Therefore， it inevitably left a hidden danger for the occurrence of the disease， which led to serious disease， while the local seedlings were just the opposite[6]. Relationship with planting density and slope aspect
The survey on the planting areas under the same conditions found that the ventilation and light transmission became poor with the increase of planting density， while the humidity become larger， which was conductive to the spread ， invasion and harm of pathogens， resulting in severe incidence. The cultivated slope aspect of the orchard also had a certain relationship with the occurrence of canker disease. The incidence was more severe in the sunny slope than in the shade slope， the incidence was more severe in the south slope than in the east and west slopes， and the incidence was more severe in the windward slope than in the leeward slope， and more severe at the top of hills than in the midslope or lowlying area. Li et al.[13]， Zhang et al.[10]， Wang et al.[4] and Hu et al.[14] proved the above conclusion.
Relationship with soil
The occurrence of canker disease has a correlation with the soil property. The survey found that in the same area under the same management conditions， the infective degrees of canker disease were different for different soil conditions. The kiwifruit plants grew well and the incidence of canker disease was low in the soil which was slightly acidic and high in organic matter content， rich in mineral nutrients with good permeability. On the other hand， the kiwifruit plants showed poor growth vigor and the incidence of canker disease was server in the soil which was hardened with poor permeability and neutral alkaline， or soil with shallow soil layer， coarse sand and poor water retention capacity. The incidence was serious for the soil which belongs to sticky kiln clay. The survey results showed that the canker disease was found in the 3yearold trees in the field with the soil of such kind in Liupanshui， indicating that sticky kiln clay was completely unsuitable for the growth of kiwifruit plants.
Relationship with fertilization
The incidence rate of canker disease could be controlled below 1% through the application of composted manure or special organic fertilizers， combined use of phosphorus and potassium fertilizers， timely addition of trace elements， and timely topdressing coped with fine management， deep tillage and weeding. The orchards only applied with nitrogen fertilizer but no scientific use of phosphorus， potassium fertilizers and trace elements could easily have soil compaction， poor permeability， and the extensive management of the orchard， untimely topdressing in later stage， or the application of not fully composted manure made it easy to burn the roots， weaken the growth vigor of kiwifruit trees， leading to poor disease resistance and server incidence. In the meantime， phosphorus deficiency could affect the plant absorption of boron， and the deficiencies of phosphorus and boron made it more easier to infect canker disease， which could make the incidence rate reach up to over 80%. However， the orchard applied with fully composted manure and strawbased fertilizers usually showed strong growth vigor of kiwifruit trees， strong disease resistance， little or no disease incidence[5]. Relationship with management level
The field management level had great impact on the occurrence of canker disease. Higher and finer management level cold have low infective degree of canker disease. The orchard with herbicides application usually had earlier incidence for the orchards adopted artificial weeding， and the infective degree was more severe. For the same orchard， test showed that the growth vigor of plants was poor in the plot applied herbicides， and the incidence rate reached up to 78.6% in the 5th year， while the rate was only 3.5% for the plot with artificial weeding. The reason was that herbicides could damage plant growth， destroy soil microbial system， affecting the healthy growth of plants. The infective degree was light if effective measures could be taken to prevent frost according to the climatic conditions and carry out timely fertilization and irrigation； scientific pruning， timely disinfection of the whole orchard， timely disinfection treatment to fruit wounds， scientific control of pests and disease （brown spot， powdery mildew， dung beetles， leaf beetles） could create healthy growth environment for the trees， thereby lightening the infective degree and achieving the effective control of the occurrence of canker disease. Otherwise， the orchards extensive management of orchards， overpruning， delayed harvest， not timely control of pests and diseases had poor grow vigor of trees， which was conducive to the occurrence of kiwifruit canker disease， even leading to severe occurrence. The above survey results showed that improving field management level was of great significance in the prevention of the occurrence of kiwifruit canker disease.
Agricultural Biotechnology2018
Comprehensive Control Measures for Bacterial Canker Disease of Kiwifruit
The control of bacterial canker disease of kiwifruit is related to crop plants， pathogenic organisms and environmental conditions. Therefore， comprehensive utilization of agricultural， physical， biological， chemical and other comprehensive measures is necessary to effectively prevent or control the occurrence and development of the disease， so as to control the economic losses within the limits， and to get the maximum economic efficiency with the least investment.
Stepping up plant quarantine
Kiwifruit bacterial canker disease belongs to the quarantine objects of the forests throughout China， so quarantine work plays an important role in controlling the spread of bacteria. Therefore， it can carry out seed and stock quarantine to the transferred seedlings during the seedling transportation， prohibit the circulation of seedlings without quarantine to nip the pathogenic bacteria in the bud to prevent the spread of the disease， and thus strengthening the implementation of quarantine is an effective means to prevent the spread of the disease. Setting up diseasefree nursery base
Setting up diseasefree nursery base of kiwifruit in the local diseasefree areas can avoid the weak tree growth vigor and poor disease resistance of seedlings caused by the water loss during the longdistance transportation， thereby improving the antirisk capability of introducing the source of the disease from the affected area， ensuring the control and management of diseasefree conditions of seedlings and other breeding materials. During the breeding period， the control of pests and diseases can be effectively strengthened. The sale of seedlings must be strictly inspected to ensure the transfer or sale of nontoxic seedlings to prevent the spread of the disease.
Breeding resistant varieties
Breeding resistant varieties is one of the effective measures to control plant diseases. China has a large number of kiwifruit germplasm resources， so the varieties with resistance can be identified and screened， which can effectively use the resistance genes in plant populations to develop resistant varieties， getting access to diseaseresistant varieties. Therefore， the wild kiwifruit varieties with stronger disease resistance can be used as rootstocks to cultivate diseaseresistant seedlings by grafting， and we can also introduce and popularize varieties with high disease resistance such as Jinkui， Guizhang and Qinxiang.
Biological control
Biological control not only can control pests and diseases， but also to avoid the harm of pesticide residues， as well as avoid host resistance. It is not only effectively protect the ecological environment， but also produce green safe food. The use of biological control is an effective way of controlling bacterial canker disease of kiwifruit. The use of beneficial microorganisms， beneficial bacteria to control bacterial canker disease of kiwifruit has achieved good effect. Song et al.[15] isolated an actinomycete which showed good effect on controlling bacterial canker disease of kiwifruit； Huang et al.[16] reported that actinomycetes TGNBSA5 had good antagonistic effect on kiwifruit canker disease； Wei et al.[17] found that polyhydroxy dinaphthaldehyde extracts （WCT） had significant effect on inhibiting the Pseudomonas syringae pv. actinidiae in kiwifruit at the mass concentration of 50 mg/mL， which could also induced the disease resistance of the hosts， and the relative control effect on kiwifruit canker disease was 69.3 %. It also found that the agents like 0.15% Wuningmycin， Zhongshengmycin and streptomycin also had good effect on controlling kiwifruit canker disease. Chemical control
Currently， chemical control is dominated in the control of bacterial canker disease of kiwifruit. The control of kiwifruit canker disease cannot wait until the outbreak of the disease， but should begin at the key period from late February to early April every year through the application of drugs in advance. In China， research was carried out to screen the indoor and field chemical agents of benzothiazone， 95% CT powder， 72% streptomycin sulfate， streptomycin， 90% oxytetracycline， cocide， 64% metidaxyl， dioctyl divinyltriamino glycine， 20% bronopol， oxadixyl， kasumin+bordeaux and polymyxin. The results showed that the above agents all had good antibacterial and control effects on the bacterial canker disease of kiwifruit[18-22]. In the process of using， the agents could be used alternately with 0.15% of Wudingmycin agent， Zhongshengmycin and streptomycin to delay or avoid the generation of plant drug resistance， so as to control the disease damage within a certain range， thereby reducing the yield loss to the minimum.
Strengthening field integrated management
We must attach great importance to field cultivation and management， improve the ability of comprehensive disease resistance of trees， and effectively control the occurrence of canker disease. First， make scientific pruning. After the fall， try to avoid wounds on the plant， and spread on benzophenone， preservative oil and other protective agent to the pruning cut when pruning. Second， make scientific fertilization. The fertilization should be balanced， and organic fertilizers and phosphorus and potassium fertilizers should be applied more， while appropriate amount of boron fertilizer should be added. Topdressing should be timely during the fruitbearing period and after fruitpicking. Leaf fertilizers should also be added， which can improve the disease resistance of the hosts and prevent the occurrence of canker disease. In addition， it also should make appropriate fruit bearing amount， to build up the growth vigor of trees， so as to improve the disease resistance of trees. Weeding and orchard cleaning should be done timely， but chemical herbicides should be avoided. The affected plants and branches should be cleared off. In autumn， the tree trunks should be smeared with protective agents to prevent cold damage， but scientific use should be made to the hormone antifreeze agents. It can also conduct film mulching to enhance the frost resisting ability. Proper agents should be used to control the pests and diseases timely. In summary， the survey and related tests showed that to achieve effective control of the bacterial canker of kiwifruit， it must adopt the combination of cultivation with management， and stick to the integrated control policy of focusing on prevention assisted with treatment. According to the conditions of different trees， 6-10 kg of Xinnong organic fertilizer could be applied once after the harvest of fruits， and once in May of the following year. Moreover， the 1 000 times diluted 6% ascorbic acid aqueous solution can be applied before the opening period of the buds of kiwifruit in early April every year， and sprayed 1-2 times during the fruit inflating period and then sprayed 1 times after the fruit harvesting， which could improve the physiological characteristics of kiwifruit， increase the resistance of kiwifruit， and effectively control the occurrence and damage of kiwifruit canker disease， thereby reducing the economic losses of fruit growers.
References
[1] TAKIKAWA Y， SERIZAWA S， ICHIKAWA T， et al. Pseudomonas syringae pv. actinidae pv. nov. the causal bacteriun of canker of kiwifruit in Japan[J]. Annals of the Phytopathological Society of Japan， 1989， 55 （4）： 437-444.
[2] GAO XN， ZHAO ZB， HUANG QL， et al. Advances in research on bacterial canker of kiwifruit[J]. Chinese Journal of Fruit Science， 2012， 29 （2）： 262-268.
[3] ZHAO LN， HU JY， YE ZF， et al. Molecular identification and pathogenicity detection of pathogen of Pseudomonas syringae pv. actinidae[J]. Journal of Huazhong Agricultural University， 2012， 31 （5）： 604-608.
[4] WANG ZR， GAO TC， GU CT， et al. Study on control of kiwifruit canker[J]. Jounral of Anhui Agricultural Sciences， 1998， 26 （4）： 349-351.
[5] LIU SJ， TANG XF， WANG ZS， et al. The occurrence rule of kiwifruit canker disease in Cangxi， Sichuan Province[J] .China Fruits， 1996， 1： 25-26.
[6] LI YZ， SONG XB， ZHANG XW， et al. Studies on the laws of occurrence of bacterial canker in kiwifruit[J]. Journal of Northwest Forestry University， 2000， 15 （2）： 53-56.
（Continued on page 69）
Key words Bacterial canker disease of kiwifruit； Occurrence； Influencing factors； Control
Received： November 25， 2017 Accepted： January 25， 2018
Supported by the Fund Project for the Growth of Young Scientific Talents of the Department of Education of Guizhou Province （Qianjiaoguhe KY[2016]No. 269）； the Openend Fund for the Key Laboratory of Green Pesticide and Agricultural Bioengineering of the Ministry of Education， Guizhou University （2016GDGP0101）； the Projects for Undergraduates of Liupanshui Teachers Normal University （LPSSYDXS1613）.
Kai YAN （1981-）， male， P. R. China， master， agronomist， devoted to research about plant protection， Email： pxyankai@126.com.
*Corresponding author. Email： lk81@163.com
Since the discovery in Japan in 1980[1]， bacterial canker disease of kiwifruit has occurred in the kiwifruit producing areas all over the world. Widespread， pathogenic， difficult to eradicate and spreading rapidly， the disease is one of the most dangerous diseases for kiwifruit， leading to the great production reduction， high mortality rate of fruit trees. Some orchards even have been destroyed， resulting in great economic losses. It is a kind of world devastating bacterial diseases， which is threatening the development of world kiwifruit industry[2].
The pathogen of kiwifruit canker in Chinas kiwifruit producing area is mainly Pseudomonas syringae pv. actinidae （Psa）[3]. In recent years， with the adjustment of agricultural structure in Guizhou， the kiwifruit industry has got the continuous development with the continuous increase of planting area. On the other hand， the occurrence and harm of the bacterial canker kiwifruit disease in kiwifruit are becoming more and more common and serious. After the occurrence of kiwifruit disease， the yield is reduced with pericarp becoming thicker， taste sourer， fruit colar poorer， and so the fruit quality also declines[4]. Therefore， survey was conducted to investigate the occurrence laws of bacterial canker disease of kiwifruits in Liupanshui area， Guizhou Province， and the comprehensive control measures were put forward in order to provide reference for the effective control of the disease， so as to promote the healthy development of the kiwifruit industry in Guizhou Province. Occurrence and Symptoms of Bacterial Canker Disease of Kiwifruit
Pathogenic bacteria tend to invade the host body before and after flower bud formation from the stem shoots， fallen leaves scars， lenticels， and branches of the plants， mainly lurking over the winter in the diseased plants. The early spring （from late February to early March） is the period with the appropriate temperature for the activities of the pathogenic bacteria， when the harm of the bacteria begins. The pathogenic bacteria can endanger the trunk， branches， vines， leaves and buds and other parts of plants， and the pathogen damage peak appears before or after the bleeding exudation. Then， the pathogenic bacteria stop the activity with temperature rise and go through the summer and winter in the hosts， becoming the source of initial infection of the following year to continue the damage[5]. The bacteria can be transmitted by means of wind and rain， insects， manmade pruning， and can form multiple reinfection from the bacteria ooze from the affected parts of plants[6]. After infection， stems and branches of diseased plants show cortical water stains at the beginning， the tissues became soft and necrotic， gradually separated from the xylem， and then cracked. When the climate became humid， they produced milky white bacterial liquid， which turns brown or rusty after bleeding exudation[7]. Scabs can rapidly expand around the stem， the pathogen can invade the xylem， and after stripping the diseased cortex， the scab xylem is black， phloem ulcer rots， resulting in difficulty in transporting and absorbing the nutrients for the trees， weak tree bodies， even death in severe cases； The infected vines are watery and dark green. After infected， the upper cotyledons become curly， the leaf margins are scorched， and then the vines or shoots die after the enlargement of the scabs. Late spring and early summer and late autumn and early winter are the peak season for the occurrence in leaves. The newly born leaves first form watery greenish dots on the leaves after infection， sometimes red dots， which then develop into irregular polygonal brown or dark brown scabs with yellow rings of 2-5 mm. The scabs can expand rapidly under the conditions of continuous low temperature and humidity， making the leaf margin scorched， leaves curled. Sometimes there is no yellow rings， but atherosclerotic pathogens can be seen oozed from the back of leaves. From late April to mid May， buds generally cannot open after infection， and for those with light infection which can have flowers open， even they can grow into fruits， the fruits are small， which can be easy to fall off or become deformed fruits. Most of the infected buds turn brown and fall off[8]. For the kiwifruit fruits which are acupunctured to inoculate the pathogens， the pathogens do not expand into scabs， and only slightly become brown at the inoculation site. Factors Affecting the Occurrence of Bacterial Canker Disease of Kiwifruit
Relationship with climatic conditions
According to the survey results， the occurrence of kiwifruit canker disease was closely related to climatic conditions such as temperature， frost and altitude in the planting area. The climatic conditions of low temperature and high humidity were conducive to the occurrence and prevalence of kiwifruit canker disease. The longer duration of frostfree period， the less incidence of the disease， and the shorter duration of frostfree period， the more serious the disease. In the meantime， the higher the altitude， the more severe the disease. The survey found that in the same plantation， there was no incidence in the valley at the minimum altitude of 1 200 m， and the incidence rate was 18.5% at the highest altitude of 1 500 m. In the mountainous area of Guizhou， the temperature decreased with the increase of altitude， the humidity was great in spring and winter because of fog， and the frostfree period was short， making the plants vulnerable to cold damage， thereby resulting in serious incidence. The results were consistent with the findings of Wang， Li and others[4-6].
Relationship with kiwifruit varieties
It has found that there are differences in the resistance to canker disease between different kiwifruit varieties. The survey found that the general trend in cultivars in this region was that Hongyang had the most serious attack， and Guizhang： was the most resistant to disease. In the meantime， the wild plants and the seedlings were generally more resistant to the canker disease， and for the same variety， the one with wild kiwifruit as stock had higher resistance to the disease， which was consistent with the results of Li[9].
Relationship with the age of kiwifruit
The survey results showed that the incidence of trees of different age groups was different. In the affected planting area， there was no canker occurrence for the young trees of 1-3 years old. However， with the increase of tree ages， the fruit bearing amount increased， and the incidence rate and damage degree of canker disease also became more serious. The infection was more serious in the old planting area than the new one. The reason might be that with the increase of tree ages， the nutrition consumption for the kiwi tress became more after the fruiting entered the full bearing stage， then the tree vigor became weak， disease resistance declined， and combined with the accumulation of pathogens， it was conducive to the occurrence of disease. The incidence rate was low for young trees， and the damage degree was light， because the young trees mainly proceeded with the accumulation of nutrients in trees， and the plants could grow well， thereby showing strong disease resistance[6]. Relationship with the bearing amount of kiwifruit
According to the survey， for the orchards with the trees of the same age under the same management level， the one conducted with artificial pollination had high fruiting rate， almost no deformed fruits， yield reaching 36 000 kg/hm2， and weak tree growth vigor， while the other proceeded with natural pollination because of the shortage of manpower had more deformed fruits which were picked in the early period， low fruiting rate， yield of only 8 250 kg/hm2， and strong tree growth vigor. In the following year， the extreme climate led to the outbreak of canker disease， the incidence rate of the plot with high fruiting rate and yield reached up to 13.7%， while the plot with low fruiting rate and yield only had the incidence rate of 2.4%. The reason was that the large fruit bearing amount overconsumed the nutrients from the trees， resulting in plant nutrition disorders， disease resistance reduction， further leading to serious occurrence， which was consistent with the results of Zhang et al.[10]， Feng et al.[11] and Jin et al.[12]. At the same time， overuse of fruitexpander by fruit growers overburdened the fruit bearing amounts of fruit trees， which could also cause excessive consumption of nutrients and weaken the growth vigor of trees， making the trees more susceptible to canker disease. Delayed harvesting overconsumed tree nutrition and shortened the key period for the trees to store effective nutrients， resulting in poor plant resistance， declined tree vigor， thereby increasing the risk for the trees to infect canker disease.
Relationship with the seedling sources of kiwifruit
The survey found that in the same plantation， for the 6yearold seedlings under the same management conditions， the incidence of seedlings imported from Sichuan was 58.2%， showing severe incidence； there was no occurrence of canker disease for the local nursery seedlings for the first year， and the incidence in the following year was only 4.7%， which showed low index of decease infection and relatively late tree age for the incidence. The reason was that Sichuan was the place with early onset of kiwifruit canker disease， belonging to the epidemic area； the longdistance transportation resulted in water loss of some seedlings， which required a long time to regain the growth， so the nutrients could not be effectively accumulated in trees， which was not favorable for the improvement of disease resistance. Therefore， it inevitably left a hidden danger for the occurrence of the disease， which led to serious disease， while the local seedlings were just the opposite[6]. Relationship with planting density and slope aspect
The survey on the planting areas under the same conditions found that the ventilation and light transmission became poor with the increase of planting density， while the humidity become larger， which was conductive to the spread ， invasion and harm of pathogens， resulting in severe incidence. The cultivated slope aspect of the orchard also had a certain relationship with the occurrence of canker disease. The incidence was more severe in the sunny slope than in the shade slope， the incidence was more severe in the south slope than in the east and west slopes， and the incidence was more severe in the windward slope than in the leeward slope， and more severe at the top of hills than in the midslope or lowlying area. Li et al.[13]， Zhang et al.[10]， Wang et al.[4] and Hu et al.[14] proved the above conclusion.
Relationship with soil
The occurrence of canker disease has a correlation with the soil property. The survey found that in the same area under the same management conditions， the infective degrees of canker disease were different for different soil conditions. The kiwifruit plants grew well and the incidence of canker disease was low in the soil which was slightly acidic and high in organic matter content， rich in mineral nutrients with good permeability. On the other hand， the kiwifruit plants showed poor growth vigor and the incidence of canker disease was server in the soil which was hardened with poor permeability and neutral alkaline， or soil with shallow soil layer， coarse sand and poor water retention capacity. The incidence was serious for the soil which belongs to sticky kiln clay. The survey results showed that the canker disease was found in the 3yearold trees in the field with the soil of such kind in Liupanshui， indicating that sticky kiln clay was completely unsuitable for the growth of kiwifruit plants.
Relationship with fertilization
The incidence rate of canker disease could be controlled below 1% through the application of composted manure or special organic fertilizers， combined use of phosphorus and potassium fertilizers， timely addition of trace elements， and timely topdressing coped with fine management， deep tillage and weeding. The orchards only applied with nitrogen fertilizer but no scientific use of phosphorus， potassium fertilizers and trace elements could easily have soil compaction， poor permeability， and the extensive management of the orchard， untimely topdressing in later stage， or the application of not fully composted manure made it easy to burn the roots， weaken the growth vigor of kiwifruit trees， leading to poor disease resistance and server incidence. In the meantime， phosphorus deficiency could affect the plant absorption of boron， and the deficiencies of phosphorus and boron made it more easier to infect canker disease， which could make the incidence rate reach up to over 80%. However， the orchard applied with fully composted manure and strawbased fertilizers usually showed strong growth vigor of kiwifruit trees， strong disease resistance， little or no disease incidence[5]. Relationship with management level
The field management level had great impact on the occurrence of canker disease. Higher and finer management level cold have low infective degree of canker disease. The orchard with herbicides application usually had earlier incidence for the orchards adopted artificial weeding， and the infective degree was more severe. For the same orchard， test showed that the growth vigor of plants was poor in the plot applied herbicides， and the incidence rate reached up to 78.6% in the 5th year， while the rate was only 3.5% for the plot with artificial weeding. The reason was that herbicides could damage plant growth， destroy soil microbial system， affecting the healthy growth of plants. The infective degree was light if effective measures could be taken to prevent frost according to the climatic conditions and carry out timely fertilization and irrigation； scientific pruning， timely disinfection of the whole orchard， timely disinfection treatment to fruit wounds， scientific control of pests and disease （brown spot， powdery mildew， dung beetles， leaf beetles） could create healthy growth environment for the trees， thereby lightening the infective degree and achieving the effective control of the occurrence of canker disease. Otherwise， the orchards extensive management of orchards， overpruning， delayed harvest， not timely control of pests and diseases had poor grow vigor of trees， which was conducive to the occurrence of kiwifruit canker disease， even leading to severe occurrence. The above survey results showed that improving field management level was of great significance in the prevention of the occurrence of kiwifruit canker disease.
Agricultural Biotechnology2018
Comprehensive Control Measures for Bacterial Canker Disease of Kiwifruit
The control of bacterial canker disease of kiwifruit is related to crop plants， pathogenic organisms and environmental conditions. Therefore， comprehensive utilization of agricultural， physical， biological， chemical and other comprehensive measures is necessary to effectively prevent or control the occurrence and development of the disease， so as to control the economic losses within the limits， and to get the maximum economic efficiency with the least investment.
Stepping up plant quarantine
Kiwifruit bacterial canker disease belongs to the quarantine objects of the forests throughout China， so quarantine work plays an important role in controlling the spread of bacteria. Therefore， it can carry out seed and stock quarantine to the transferred seedlings during the seedling transportation， prohibit the circulation of seedlings without quarantine to nip the pathogenic bacteria in the bud to prevent the spread of the disease， and thus strengthening the implementation of quarantine is an effective means to prevent the spread of the disease. Setting up diseasefree nursery base
Setting up diseasefree nursery base of kiwifruit in the local diseasefree areas can avoid the weak tree growth vigor and poor disease resistance of seedlings caused by the water loss during the longdistance transportation， thereby improving the antirisk capability of introducing the source of the disease from the affected area， ensuring the control and management of diseasefree conditions of seedlings and other breeding materials. During the breeding period， the control of pests and diseases can be effectively strengthened. The sale of seedlings must be strictly inspected to ensure the transfer or sale of nontoxic seedlings to prevent the spread of the disease.
Breeding resistant varieties
Breeding resistant varieties is one of the effective measures to control plant diseases. China has a large number of kiwifruit germplasm resources， so the varieties with resistance can be identified and screened， which can effectively use the resistance genes in plant populations to develop resistant varieties， getting access to diseaseresistant varieties. Therefore， the wild kiwifruit varieties with stronger disease resistance can be used as rootstocks to cultivate diseaseresistant seedlings by grafting， and we can also introduce and popularize varieties with high disease resistance such as Jinkui， Guizhang and Qinxiang.
Biological control
Biological control not only can control pests and diseases， but also to avoid the harm of pesticide residues， as well as avoid host resistance. It is not only effectively protect the ecological environment， but also produce green safe food. The use of biological control is an effective way of controlling bacterial canker disease of kiwifruit. The use of beneficial microorganisms， beneficial bacteria to control bacterial canker disease of kiwifruit has achieved good effect. Song et al.[15] isolated an actinomycete which showed good effect on controlling bacterial canker disease of kiwifruit； Huang et al.[16] reported that actinomycetes TGNBSA5 had good antagonistic effect on kiwifruit canker disease； Wei et al.[17] found that polyhydroxy dinaphthaldehyde extracts （WCT） had significant effect on inhibiting the Pseudomonas syringae pv. actinidiae in kiwifruit at the mass concentration of 50 mg/mL， which could also induced the disease resistance of the hosts， and the relative control effect on kiwifruit canker disease was 69.3 %. It also found that the agents like 0.15% Wuningmycin， Zhongshengmycin and streptomycin also had good effect on controlling kiwifruit canker disease. Chemical control
Currently， chemical control is dominated in the control of bacterial canker disease of kiwifruit. The control of kiwifruit canker disease cannot wait until the outbreak of the disease， but should begin at the key period from late February to early April every year through the application of drugs in advance. In China， research was carried out to screen the indoor and field chemical agents of benzothiazone， 95% CT powder， 72% streptomycin sulfate， streptomycin， 90% oxytetracycline， cocide， 64% metidaxyl， dioctyl divinyltriamino glycine， 20% bronopol， oxadixyl， kasumin+bordeaux and polymyxin. The results showed that the above agents all had good antibacterial and control effects on the bacterial canker disease of kiwifruit[18-22]. In the process of using， the agents could be used alternately with 0.15% of Wudingmycin agent， Zhongshengmycin and streptomycin to delay or avoid the generation of plant drug resistance， so as to control the disease damage within a certain range， thereby reducing the yield loss to the minimum.
Strengthening field integrated management
We must attach great importance to field cultivation and management， improve the ability of comprehensive disease resistance of trees， and effectively control the occurrence of canker disease. First， make scientific pruning. After the fall， try to avoid wounds on the plant， and spread on benzophenone， preservative oil and other protective agent to the pruning cut when pruning. Second， make scientific fertilization. The fertilization should be balanced， and organic fertilizers and phosphorus and potassium fertilizers should be applied more， while appropriate amount of boron fertilizer should be added. Topdressing should be timely during the fruitbearing period and after fruitpicking. Leaf fertilizers should also be added， which can improve the disease resistance of the hosts and prevent the occurrence of canker disease. In addition， it also should make appropriate fruit bearing amount， to build up the growth vigor of trees， so as to improve the disease resistance of trees. Weeding and orchard cleaning should be done timely， but chemical herbicides should be avoided. The affected plants and branches should be cleared off. In autumn， the tree trunks should be smeared with protective agents to prevent cold damage， but scientific use should be made to the hormone antifreeze agents. It can also conduct film mulching to enhance the frost resisting ability. Proper agents should be used to control the pests and diseases timely. In summary， the survey and related tests showed that to achieve effective control of the bacterial canker of kiwifruit， it must adopt the combination of cultivation with management， and stick to the integrated control policy of focusing on prevention assisted with treatment. According to the conditions of different trees， 6-10 kg of Xinnong organic fertilizer could be applied once after the harvest of fruits， and once in May of the following year. Moreover， the 1 000 times diluted 6% ascorbic acid aqueous solution can be applied before the opening period of the buds of kiwifruit in early April every year， and sprayed 1-2 times during the fruit inflating period and then sprayed 1 times after the fruit harvesting， which could improve the physiological characteristics of kiwifruit， increase the resistance of kiwifruit， and effectively control the occurrence and damage of kiwifruit canker disease， thereby reducing the economic losses of fruit growers.
References
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[2] GAO XN， ZHAO ZB， HUANG QL， et al. Advances in research on bacterial canker of kiwifruit[J]. Chinese Journal of Fruit Science， 2012， 29 （2）： 262-268.
[3] ZHAO LN， HU JY， YE ZF， et al. Molecular identification and pathogenicity detection of pathogen of Pseudomonas syringae pv. actinidae[J]. Journal of Huazhong Agricultural University， 2012， 31 （5）： 604-608.
[4] WANG ZR， GAO TC， GU CT， et al. Study on control of kiwifruit canker[J]. Jounral of Anhui Agricultural Sciences， 1998， 26 （4）： 349-351.
[5] LIU SJ， TANG XF， WANG ZS， et al. The occurrence rule of kiwifruit canker disease in Cangxi， Sichuan Province[J] .China Fruits， 1996， 1： 25-26.
[6] LI YZ， SONG XB， ZHANG XW， et al. Studies on the laws of occurrence of bacterial canker in kiwifruit[J]. Journal of Northwest Forestry University， 2000， 15 （2）： 53-56.
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