Gyoung Hee Kim

Outbreak of bacterial canker on Hort16A (Actinidia chinensis Planchon) caused by Pseudomonas syringae pv. actinidiae in Korea

Abstract Bacterial canker was first observed on the kiwifruit cv. ‘Hort16A (Actinidia chinensis)’ in Jeju Province, Korea, in spring 2006. Die back or blight on young canes, often with red-rusty exudation on canes or trunks, and dark brown irregular spots surrounded with yellowish halos on leaves are the typical symptoms. These symptoms closely resemble those caused by Pseudomonas syringae pv. actinidiae on the kiwifruit cv. ‘Hayward (Actinidia deliciosa)’. A sudden outbreak and rapid spread of the bacterial canker resulted in the death of severely infected vines and eradication of completely devastated orchards of the kiwifruit cv. ‘Hort16A’. Contaminated pruning shears and climatic conditions appear to have been responsible for the sudden outbreak and rapid spread of the epidemics on the kiwifruit cv. ‘Hort16A’ vines. The causal bacterium was isolated from diseased vines of the kiwifruit cv. ‘Hort16A’ and identified as P. syringae pv. actinidiae, which is the same bacterial pathogen responsible for cankers on the kiwifruit cv. ‘Hayward’ by morphological, cultural, physiological and biochemical, molecular and pathogenicity analyses.

Occurrence of a New Type of Pseudomonas syringae pv. actinidiae Strain of Bacterial Canker on Kiwifruit in Korea

Pseudomonas syringae pv. actinidiae strains, the causal agents of bacterial canker on kiwifruit, were isolated from Korea and Italy in 2011. Among 87 isolates, a total of six representative strains, three from Korea and three from Italy, were identified on the basis of biochemical and physiological tests. Identities were confirmed by PCR using P. syringae pv. actinidiae-specific primers PsaF1/R2, which amplified a 280-bp DNA fragment. The strains isolated from Korea in this study displayed BOX-PCR patterns similar to those isolated from Italy but different from those isolated previously in Korea or the pathotype P. syringae pv. actinidiae strain. The effector hopA1 and hopH1 genes, which are known to be present in strains isolated recently from France and Italy, were also present in P. syringae pv. actinidiae strains, SYS1, SYS2 and SYS4, isolated from Korea in this work. However, no amplicons of the expected size were obtained from strains previously isolated from Korea and Japan. In addition, the Korean strains isolated in this work belonged to haplotype I for the cts gene identical to those strains isolated from recent outbreaks in Italy. These results suggest that P. syringae pv. actinidiae strains isolated from Korea and examined in this work are a new type of strain similar to those found from recent outbreaks in Italy. This is the first report on the occurrence of cts haplotype I strains of P. syringae pv. actinidiae affecting kiwifruit plants in Korea.

Molecular Characteristics of Pseudomonas syringae pv. actinidiae Strains Isolated in Korea and a Multiplex PCR Assay for Haplotype Differentiation.

The molecular features of Pseudomonas syringae pv. actinidiae strains isolated in Korea were compared with strains isolated in Japan and Italy. Sequencing of eight P. syringae pv. actinidiae and three P. syringae pv. theae strains revealed a total of 44 single nucleotide polymorphisms across 4,818 bp of the concatenated alignment of nine genes. A multiplex PCR assay was developed for the detection of P. syringae pv. actinidiae and for the specific detection of recent haplotype strains other than strains isolated since the 1980s in Korea. The primer pair, designated as TacF and TacR, specifically amplified a 545-bp fragment with the genomic DNA of new haplotype of P. syringae pv. actinidiae strains. A multiplex PCR conducted with the TacF/TacR primer pair and the universal primer pair for all P. syringae pv. actinidiae strains can be simultaneously applied for the detection of P. syringae pv. actinidiae and for the differentiation of new haplotype strains.

Pectobacterium carotovorum subsp. actinidiae subsp. nov., a new bacterial pathogen causing canker-like symptoms in yellow kiwifruit, Actinidia chinensis

Abstract In this study, symptoms closely resembling those caused by Pseudomonas syringae pv. actinidiae were found in kiwifruit plants (Actinidia chinensis cv. Hort16A) growing in Jeju province, Korea. Bacterial strains including strain KKH3T were isolated from representative lesions on kiwifruit plants. Comparative 16S rRNA gene sequence-based phylogenetic analysis placed these bacteria in a separate cluster within the genus Pectobacterium. Strain KKH3T showed the highest similarity (98.7%) to the recognised bacteria Pectobacterium carotovorum subsp. carotovorum and Pectobacterium wasabiae. To justify subspecies level differentiation, the partial nucleotide sequences of atpD, carA and recA from strain KKH3T were compared with those from other members of the family Enterobacteriaceae. Distant relationships between strain KKH3T and six reference strains of Pectobacterium spp. were evident in the phylogenetic tree. The results of the DNA–DNA hybridisation and polyphasic analysis revealed that strain KKH3T belongs to another subspecies of P. carotovorum, for which the name Pectobacterium carotovorum subsp. actinidiae subsp. nov. is hereby proposed.

Outbreak and Spread of Bacterial Canker of Kiwifruit Caused by Pseudomonas syringae pv. actinidiae Biovar 3 in Korea

A bacterial pathogen, Pseudomonas syringae pv. actinidiae (Psa), is a causal agent of kiwifruit bacterial canker worldwide. Psa biovar 3 (Psa3) was first detected in 2011 at an orchard in Dodeok-myeon, Goheunggun, Jeonnam Province in Korea. In this study, we present the results of an epidemiological study regarding Psa3 occurrence on kiwifruit orchards in Korea for the period of 2013 to 2015. Since the first detection of Psa3 in 2011, there was no further case reported by 2013. However, Psa3 was rapidly spreading to 33 orchards in 2014; except for three orchards in Sacheonsi, Gyeongnam Province, most cases were reported in Jeju Island. Entering 2015, bacterial canker by Psa3 became a pandemic in Korea, spreading to 72 orchards in Jeju Island, Jeonnam, and Gyeongnam Provinces. Our epidemiological study indicated that the first Psa3 incidence in 2011 might result from an introduction of Psa3 through imported seedlings from China in 2006. Apart from this, it was estimated that most Psa3 outbreaks from 2014 to 2015 were caused by pollens imported from New Zealand and China for artificial pollination. Most kiwifruit cultivars growing in Korea were infected with Psa3; yellow-fleshed cultivars (Yellow-king, Hort16A, Enza-gold, Zecy-gold, and Haegeum), red-fleshed cultivars (Hongyang and Enza-Red), green-fleshed cultivars (Hayward and Daeheung), and even a kiwiberry (Skinny-green). However, susceptibility to canker differed among cultivars; yellow- and red-fleshed cultivars showed much more severe symptoms compared to the green-fleshed cultivars of kiwifruit and a kiwiberry.

Optimal Spray Time, Interval and Number of Preventive Fungicides for the Control of Fruit Rots of Green and Gold Kiwifruit Cultivars

Optimal spray time, interval and number of preventive fungicides against fruit rots of kiwifruit wereinvestigated at the orchard which both green kiwifruit cultivar ‘Hayward’ and gold kiwifruit cultivar‘Hort16A’ are cultivating side by side during 2009 and 2010 growing seasons in Jeju island, Korea. Thehighest control efficiency was obtained from benomyl WP and followed by thiophanate-methyl WP andcarbendazim+diethofencarb WP. The control efficacies of the fungicides were much higher when appliedonto the kiwifruit canopy after the flowering time than before the flowering time but thereafter their controlefficiencies were decreased drastically according to delays of spray timing. With increasing spray numbers ofthe fungicides, the control efficacy increased. However, optimal spray time, interval and number of thepreventive fungicides for the effective control of fruit rots of kiwifruit were determined as 4 time-sprayschedule with 2-week-interval just after the flowering time on both ‘Hayward’ and ‘Hort16A’ cultivars.Keywords : Benomyl, Carbendazim+diethofencarb, Fruit rot, Kiwifruit, Thiophanate-methyl

Development of Specific Markers for Identification of Biovars 1 and 2 Strains of Pseudomonas syringae pv. actinidiae.

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.

Isolation and Characterization of Bacteriophages Against Pseudomonas syringae pv. actinidiae Causing Bacterial Canker Disease in Kiwifruit.

Pseudomonas syringae pv. actinidiae causes bacterial canker disease in kiwifruit. Owing to the prohibition of agricultural antibiotic use in major kiwifruit-cultivating countries, alternative methods need to be developed to manage this disease. Bacteriophages are viruses that specifically infect target bacteria and have recently been reconsidered as potential biological control agents for bacterial pathogens owing to their specificity in terms of host range. In this study, we isolated bacteriophages against P. syringae pv. actinidiae from soils collected from kiwifruit orchards in Korea and selected seven bacteriophages for further characterization based on restriction enzyme digestion patterns of genomic DNA. Among the studied bacteriophages, two belong to the Myoviridae family and three belong to the Podoviridae family, based on morphology observed by transmission electron microscopy. The host range of the selected bacteriophages was confirmed using 18 strains of P. syringae pv. actinidiae, including the Psa2 and Psa3 groups, and some were also effective against other P. syringae pathovars. Lytic activity of the selected bacteriophages was sustained in vitro until 80 h, and their activity remained stable up to 50°C, at pH 11, and under UV-B light. These results indicate that the isolated bacteriophages are specific to P. syringae species and are resistant to various environmental factors, implying their potential use in control of bacterial canker disease in kiwifruits.

Occurrence and Epidemics of Bacterial Canker of Kiwifruit in Korea

Bacterial canker is the largest limiting factor in the cultivation and production of kiwifruit worldwide. Typical symptoms comprise necrotic spots on leaves, canker and dieback on canes and trunks, twig wilting, and blossom necrosis. Pseudomonas syringae pv. actinidiae (Psa), which is the causal agent of kiwifruit bacterial canker, is divided into four biovars based on multilocus sequence analysis of different genes, additional PCR testing of pathogenic genes (argKtox cluster, cfl, and various effector genes), and biochemical and physiological characterization. Bacterial canker caused by Psa biovar 2 designated Psa2 was detected for the first time on the green-fleshed kiwifruit cultivar Hayward in 1988 and the yellow-fleshed kiwifruit cultivar Hort16A in 2006 in Korea. Psa biovar 3 designated Psa3, responsible for the current global pandemics of kiwifruit bacterial canker, began to appear in Korea in 2011 and caused tremendous economic losses by destroying many vines or orchards of yellow-fleshed kiwifruit cultivars in one or several growing seasons. Bacterial canker epidemics caused by both Psa2 and Psa3 are prevalent in Korea in recent years. In this review, we summarize the symptomatology, etiology, disease cycle, diagnosis, and epidemiology of kiwifruit bacterial canker in Korea.

Spread of Bacterial Canker of Kiwifruit by Secondary Infection of Pseudomonas syringae pv. actinidiae Biovar 3 in Gyeongnam in 2016

키위(Chinese gooseberry, kiwifruit, 참다래) 재배는 1970년대 후반부터 시작되었다. 재배 초기에는 뉴 질랜드에서 육성된 그린키위 품종(Actinidia deliciosa)인 헤 이워드(Hayward)가 주종을 이루었다. 그러나 뉴질랜드에서 골드키위 품종(Actinidia chinensis)인 Hort16A가 육성되면서 전 세계적으로 골드키위 품종의 육성과 재배가 확대되기 시작했다. 우리나라에도 2004년부터 제주도에서 Hort16A 가 재배되기 시작했으며, 사용료(royalty) 대응차원에서 정 부지원으로 2000년대 후반에 국내에서 육성된 골드키위 품 종인 제시골드, 한라골드와 해금 재배면적이 급증하는 추 세이다. 또한 레드키위 품종(A. chinensis)인 홍양과 토종다래 품종들(Actinidia arguta)도 점차 재배가 증가하고 있다. 키위에 치명적인 피해를 주는 궤양병은 1984년 일본에서 재배되고 있던 헤이워드에서 처음 보고되었다(Serizawa 등, 1989; Takikawa 등, 1989). 우리나라에서도 1988년부터 제주 도에서 재배되고 있던 헤이워드에서 궤양병이 처음 발생