• Research in Plant Disease
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• v.8 no.4
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• pp.250-253
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• 2002

This research was conducted to develop a simple and effective method for pathogenicity assay of the causal agent of bacterial canker on kiwifruit. The developed method is a modified version of syringe-infiltration method that is used in the assay fer the hypersensitive response assay. Bacterial cell suspensions in 50 mM potassium phosphate buffer(pH 7.5) were infiltrated using a plastic syringe with 25G needle into primary leaves of five-year-old kiwifruit. Typical symptoms of bacterial canker were observed five days after infiltration. Symptoms developed on the leaves were detected in these inocula that treated above 10$^4$cfu/ml or above. Using this technique, host range of Pseudomonas syringae pv. actinidiae and three other plant pathogenic pseudomonads were investigated for 25 different plant species. The various symptoms were showed depend-ing on different plant species and inoculated pathogen combinations. This method has the advantage that symptoms can be showed faster compared to other methods and high humid conditions are not required.

• Research in Plant Disease
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• v.26 no.1
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• pp.44-47
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• 2020

Streptomycin resistant isolates of Pseudomonas syringae pv. actinidiae, the causal agent of bacterial canker in kiwifruit, were found in Korea. A total of 734 isolates of P. syringae pv. actinidiae collected between 2008 and 2017 from bacterial canker infections in 111 kiwifruit orchards were assessed for streptomycin resistance. The survival of each isolate was screened against 100 ㎍/ml of streptomycin. Among 734 isolates, 38 streptomycin resistant P. syringae pv. actinidiae isolates originated from nine orchards were found. Streptomycin resistant isolates belonging to biovar 2 were found in several individual years, but ones belonging to biovar 3 were found in Korea only since 2016. Therefore, to use streptomycin for control of bacterial canker in kiwifruit orchards should be very careful, and it is necessary to check the streptomycin susceptibility of the pathogen before use in kiwifruit orchards.

• Research in Plant Disease
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• v.23 no.1
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• pp.35-41
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• 2017

Pseudomonas syringae pv. actinidiae is the causative agent of bacterial canker of kiwifruit. The population of this pathogen is differentiated into three biovars, biovar 1, 2 and 3, according to their molecular characteristics. In this work, we determined biovars of P. syringae pv. actinidiae strains isolated in Korea since 1997 and stored in Department of Biology, Sunchon National University, Suncheon, Korea. The biovars of P. syringae pv. actinidiae strains were determined by PCR using biovar specific primers developed previously. Of 682 strains investigated, 288 strains belonged to biovar 2, while 394 strains were biovar 3. There were no P. syringae pv. actinidiae strains belonging to biovar 1 among the strains isolated in Korea. Sudden outbreak and spreading of bacterial canker caused by biovar 3 strain suggest that this strain has character of rapid transmission.

• The Plant Pathology Journal
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• v.31 no.4
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• pp.343-349
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• 2015

Citrus canker caused by Xanthomonas citri subsp. citri (Xcc) is one of the most important bacterial diseases of citrus. Because citrus canker is not found in many countries including European Union and Australia, Xcc is strictly regulated in order to prevent its spread. In this study, the effects of X-irradiation on Xcc growth either in the suspension or on the surface of citrus fruits were investigated. The suspension containing $1{\times}10^7cfu/ml$ of Xcc was irradiated with different absorbed doses of X-irradiation ranging from 50 to 400 Gy. The results showed that Xcc was fully dead at 400 Gy of X-irradiation. To determine the effect of X-irradiation on quarantine, the Xcc-inoculated citrus fruits were irradiated with different X-ray doses at which Xcc was completely inhibited by an irradiation dose of 250 Gy. The $D_{10}$ value for Xcc on citrus fruits was found to be 97 Gy, indicating the possibility of direct application on citrus quarantine without any side sterilizer. Beside, presence of Xcc on the surface of asymptomatic citrus fruits obtained from citrus canker-infected orchards was noted. It indicated that the exporting citrus fruits need any treatment so that Xcc on the citrus fruits should be completely eliminated. Based on these results, ionizing radiation can be considered as an alternative method of eradicating Xcc for export of citrus fruits.

• The Plant Pathology Journal
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• v.26 no.4
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• pp.299-305
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• 2010

A half-sib family of two 4-year-old seedlings of Pinus $\times$ rigitaeda was inoculated with each of 20 Pinus thunbergii isolates of Fusarium circinatum (syn. Fusarium subglutinans f. sp. pini) from two pitch canker damaged sites in Jeju Island, South Korea. Initial symptoms of needle damages were visible on most of the seedlings at 18 days after inoculation. The 20 tested isolates were not significantly different in virulence, based on lesion lengths at the site of inoculation (P = 0.217). The most virulent isolate FT-7 showed the longest lesion length. Some seedlings began to die 46 days after inoculation. All seedlings were dead by 68 days after inoculation except two seedlings inoculated with each of isolates FS-2 and FS-13, respectively. Using the FT-7, 38-year-old 11 P. $\times$ rigitaeda trees, which were survived from a seed orchard severely damaged by pitch canker, were inoculated on branches in the seed orchard in Jeju Island to assess differences in susceptibility to pitch canker. The 11 trees differed significantly (P < 0.001) in susceptibility to F. circinatum based on average lesion lengths measured 56 days after inoculation. It is possible that induced resistance contributed to their capacity to limit lesion development. The susceptibility of natural selection P. $\times$ rigitaeda trees are more likely affected by interaction with F. circinatum rather than environmental conditions.

• The Plant Pathology Journal
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• v.33 no.1
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• pp.87-94
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• 2017

Citrus canker disease decreases the fruit quality and yield significantly, furthermore, emerging of streptomycin-resistant pathogens threatens the citrus industry seriously because of a lack of proper control agents. Small synthetic antimicrobial peptides (AMPs) could be a promising alternative. Fourteen hexapeptides were selected by using positional scanning of synthetic peptide combinatorial libraries. Each hexapeptide showed different antimicrobial spectrum against Bacillus, Pseudomonas, Xanthomonas, and Candida species. Intriguingly, BHC10 showed bactericidal activity exclusively on Xanthomonas citri subsp. citri (Xcc), while BHC7 was none-active exclusively against two Pseudomonas spp. at concentration of $100{\mu}g/ml$ suggesting potential selectivity constrained in hexapeptide frame. Three hexapeptides, BHC02, 06 and 11, showed bactericidal activities against various Xcc strains at concentration of $10{\mu}g/ml$. When they were co-infiltrated with pathogens into citrus leaves the disease progress was suppressed significantly. Further study would be needed to confirm the actual disease control capacity of the selected hexapeptides.

• The Plant Pathology Journal
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• v.32 no.2
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• pp.162-167
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• 2016

Pseudomonas syringae pv. actinidiae, the causal agent of canker in kiwifruit, can be divided into three biovars (biovars 1, 2, and 3). Strains belonging to biovar 1 produce phaseolotoxin and were isolated in Japan and Italy before 2008. Strains of biovar 2 produce coronatine instead of phaseolotoxin and have been isolated only in Korea. Strains belonging to biovar 3 produce neither phaseolotoxin nor coronatine and are responsible for the global outbreak of bacterial canker of kiwifruit in recent years. The biovar 3-specific primer set was developed in a previous work. In this study, two sets of PCR primers specific to strains of biovars 1 and 2, respectively, were developed based on random amplified polymorphic DNA analyses. Primers PsaJ-F and PsaJ-R produced a 481-bp region with genomic DNA of biovar 1 strains, whereas primers PsaK-F and PsaK-R amplified a 413-bp region present only in the genome of biovar 2 strains.

• The Plant Pathology Journal
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• v.32 no.4
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• pp.363-370
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• 2016

Pseudomonas syringae pv. actinidiae (Psa) causes bacterial canker disease in kiwifruit. Antibacterial activity of plant essential oils (PEOs) originating from 49 plant species were tested against Psa by a vapor diffusion and a liquid culture assays. The five PEOs from Pimenta racemosa, P. dioica, Melaleuca linariifolia, M. cajuputii, and Cinnamomum cassia efficiently inhibited Psa growth by either assays. Among their major components, estragole, eugenol, and methyl eugenol showed significant antibacterial activity by only the liquid culture assay, while cinnamaldehyde exhibited antibacterial activity by both assays. The minimum inhibitory concentrations (MICs) of estragole and cinnamaldehyde by the liquid culture assay were 1,250 and 2,500 ppm, respectively. The MIC of cinnamaldehyde by the vapor diffusion assay was 5,000 ppm. Based on the formation of clear zones or the decrease of optical density caused by these compounds, they might kill the bacterial cells and this feature might be useful for managing the bacterial canker disease in kiwifruit.

• Journal of Korean Society of Forest Science
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• v.95 no.1
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• pp.139-144
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• 2006

Chestnut trees have been severely damaged by the various cankers in Korea. Field surveys for elucidating the relationships between disease occurrence and environmental factors, i.e., tree age, temperature, rainfall precipitation, direction, degree of slope, chemical properties of soils, and so on, were carried out in the chestnut tree plantations located at Gyeongnam, Jeonnam, Chungnam, and Gyeonggi-Do Province. Totally, one thousand and one hundred thirty seven trees from 36 experiment plots were investigated. Trees infected by at least one of the canker fungi were estimated up to 66%. The most severely infested area was Sunchon in Jeonnam Province with the rate of 80%, while the most lightly infested area was Kongju in Chungnam Province with 39%. Disease occurrence was found to be highly correlated with tree age. The disease occurred most frequently on trees ranged from 7 to 12 years old, while it was relatively low on trees below 5 years old or above 25 years old. Canker positions on the tree formed by the pathogenic fungi were most often at 1.6-2.0m above the ground. Over five hundreds bark samples from the canker area on the tree were collected and the pathogenic fungi were isolated. The most commonly isolated fungus was identified as Cryphonectria parasitica, the chestnut blight fungus.

• The Korean Journal of Mycology
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• v.40 no.4
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• pp.266-270
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• 2012

Stem canker and tuber rot symptoms were observed on yam grown in Andong and Jinju, Korea in 2011. A total of 20 isolates of Rhizoctonia and allied fungi were obtained from the symptomatic plants. Among the isolates, 8 isolates were identified as Rhizoctonia solani and 12 isolates as Ceratobasidium sp. based on rDNA-internal transcribed spacer (ITS) sequence similarity. In the cluster analysis of rDNA-ITS sequences, 7 isolates of R. solani belonged to AG 2-2IIIB and remaining one to AG 1-1A. In addition, among the 12 isolates of Ceratobasidium sp., 7 isolates belonged to AG-Fa, three isolates to AG-A and the other two isolates to AG-Fb and AG-O, respectively. Pathogenicity tests showed that all the R. solani AG 2-2IIIB isolates are pathogenic on stem and tuber of yam but R. solani AG 1-1A and all the Ceratobasidium isolates are non-pathogenic. The results indicate that R. solani AG 2-2IIIB is an important pathogen causing stem canker and tuber rot on yams grown in the study areas. This is the first report of R. solani AG 2-2IIIB causing stem canker and tuber rot of yam in Korea.