• Korean Journal Plant Pathology
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• v.14 no.4
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• pp.303-307
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• 1998

Citrus scab caused warty and scabby lesions on the surface of leaves, twigs and fruits of Satsuma mandarin. Warty lesions were mainly developed before July but scabby ones were developed during summer season in Cheju island, Korea. The casual organism of scab was morphologically identified as Sphaceloma fawcettii and was thought to be Tryon's pathotype of Elsinoe fawcettii, because it was pathogenic on rough lemon and Cleopatra mandarin but non-pathogenic on sour orange, grapefruit and sweet orange among the 5 differential hosts of E. fawcettii.

• Research in Plant Disease
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• v.21 no.3
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• pp.231-234
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• 2015

Elsinoe fawcettii and E. australis are two currently recognized scab pathogens of citrus. E. fawcettii has at least six pathotypes while E. australis has at least two pathotypes. Colonies of E. fawcettii and E. australis do not sporulate in artificial media including potato dextrose agar (PDA). Whiteside's method has been widely used for preparing conidial inoculum in vitro. This study was carried out to develop efficient method for conidia production from artificial media. We developed a shaking method which included the following steps: 1) Colony grown on PDA was mashed with a steel spatula; 2) Mycelia fragments were cultured in 50 ml sterilized rain water in a rotary shaker-incubator (180 rpm) at $25^{\circ}C$ for 24 h: 3) The conidia suspension was filtered through two layers of cheesecloth. Average conidia production of all isolates tested using this shaking method was approximately 13.1 times higher than that from Whiteside's method in this study.

• The Plant Pathology Journal
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• v.37 no.3
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• pp.268-279
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• 2021

Citrus scab, caused by the fungal pathogen Elsinoë fawcettii, is one of the most important fungal diseases affecting Citrus spp. Citrus scab affects young tissues, including the leaves, twigs, and fruits, and produces severe fruit blemishes that reduce the market value of fresh fruits. To study the molecular responses of satsuma mandarin (C. unshiu) to E. fawcettii, plant hormone-related gene expression was analyzed in response to host-compatible (SM16-1) and host-incompatible (DAR70024) isolates. In the early phase of infection by E. fawcettii, jasmonic acid- and salicylic acid-related gene expression was induced in response to infection with the compatible isolate. However, as symptoms advanced during the late phase of the infection, the jasmonic acid- and salicylic acid-related gene expression was downregulated. The gene expression patterns were compared between compatible and incompatible interactions. As scabs were accompanied by altered tissue growth surrounding the infection site, we conducted gibberellic acid- and abscisic acid-related gene expression analysis and assessed the content of these acids during scab symptom development. Our results showed that gibberellic and abscisic acid-related gene expression and hormonal changes were reduced and induced in response to the infection, respectively. Accordingly, we propose that jasmonic and salicylic acids play a role in the early response to citrus scab, whereas gibberellic and abscisic acids participate in symptom development.

• Research in Plant Disease
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• v.22 no.1
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• pp.1-8
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• 2016

Elsinoe fawcettii causing citrus scab was suppressed by rhizobacterial strains such as Burkholderia gladioli MRL408-3, TRH423-3 and Pseudomonas fluorescens THJ609-3, TRH415-2 having antifungal activity. The leaf surface of Satsuma mandarin, which was pre-treated with the rhizobacterial strains, was observed by a scanning electron microscope (SEM) after inoculation with E. fawcettii. The number of lesions was reduced on the leaves pre-treated with the rhizobacterial strains compared to those of untreated leaves. Especially, the lesions numbers was apparently reduced on the leaves pre-treated with B. gladioli MRL408-3. The observation by SEM revealed that not only the germination rate but also the length of germ tube of the pathogen were decreased on the rhizobacterial strains pre-treated leaves. These inhibition of the fungal growth was more strongly expressed on the leaves pre-treated with commercial fungicide imibenconazole, by which the lesions was rarely found on the leaves. Based on these results, it was suggested that rhizobacterial strains may inhibit the germination and growth of the E. fawcettii on the surface of citrus leaves, resulting in decrease of disease severity.

• The Plant Pathology Journal
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• v.31 no.4
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• pp.421-427
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• 2015

Citrus scab disease is one of the destructive diseases that reduce the value of fruit for the fresh market. We analyzed the process of symptom development after infection with scab pathogen $Elsino{\ddot{e}}$ fawcettii in the susceptible satsuma mandarin leaves to observe the structural modification against pathogen. The cuticle and epidermal cells along with 3-5 layers of mesophyll tissue were degraded 1-2 days post inoculation. Surrounding peripheral cells of degraded tissues grew rapidly and then enveloped the necrotic area along with the growing conidia. Cross sections through the lesion revealed hyphal colonization in epidermis and mesophyll tissues. In response to the pathogen colonization, host cell walls were lignified, inner cells were rapidly compartmentalized and a semi-circular boundary was formed that separated the infected region from the non-infected region, and finally prevented the intercellular pathogen spread.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2002.11a
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• pp.94.2-95
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• 2002

• Research in Plant Disease
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• v.26 no.1
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• pp.57-60
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• 2020

Citrus scab symptoms were observed on leaves of trifoliate orange (Poncirus trifoliata) in open field of Citrus Research Institute, National Institute of Horticultural and Herbal Science. Typical scab pustules were formed and they were elevated protuberances form and light brown to grey. The pathogens were isolated from the symptomatic leaves and then were identified to Elsinoë fawcettii by morphological characteristics, pathogenicity and PCR assay. The morphological characteristics of colonies formed very slow-growing, pulvinate, or raised and deeply fissured, gummy to mucoid or tomentose colonies on potato dextrose agar medium. The pathogens were pathogenic to leaves of Satsuma mandarin, lemon, sour orange and grapefruit with typical scab symptoms. In PCR assay, specific amplified of products of 717 bp with Efaw-1 and 384 bp with Efaw-2 were observed from trifoliate isolates and E. fawcettii as reference but not from E. australis. This is first report of trifoliate orange being positive for citrus scab disease.