Preferred name: Venturia nashicola
Authority: Tanaka & Yamamoto
Taxonomic position: Fungi: Ascomycota: Pezizomycotina: Dothideomycetes: Venturiales: Venturiaceae
Common names in English: scab of Chinese pear, scab of Japanese pear
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Notes on taxonomy and nomenclature EU Categorization: A1 Quarantine pest (Annex II A)
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EPPO Code: VENTNA

The principal hosts are Asian pears (‘nashi’) including Japanese pear (Pyrus pyrifolia var. culta) and Chinese pears (P. bretschneideri, and P. ussuriensis). V. nashicola has also been reported on various wild Pyrus spp. such as P. betulifolia (hokushimamenashi and manshumamenashi), P. aromatica (iwateyamanashi), P. vilis (Ishii et al., 2002). However, these wild species are not widely distributed and are not a significant reservoir of the pathogen. Pathological specialization has been found in V. nashicola and 7 races have been identified so far (Ishii et al., 2002; Ishii et al., in press). European pear (P. communis) has been shown not to be a host (Tanaka & Yamamoto 1964; Ishii & Yanase 2000; Ishii et al., in press). Asian pears are grown in the EPPO region, but at a much smaller scale than European pear.

Host list: Pyrus betulifolia, Pyrus bretschneideri, Pyrus calleryana, Pyrus pyrifolia var. culta, Pyrus pyrifolia, Pyrus ussuriensis var. aromatica, Pyrus ussuriensis var. hondoensis, Pyrus ussuriensis

V. nashicola is indigenous to Eastern Asia and has no history of wider spread to new areas.

Asia: China (Anhui, Hebei, Jilin, Liaoning, Shaanxi, Shandong, Shanxi, Yunnan), Japan (Hokkaido, Honshu, Kyushu, Shikoku), Korea, Republic, Taiwan

The fungus overwinters in infected leaves on the orchard floor and forms ascospores in a pseudothecium in the following spring. The fungus also overwinters in the inner tissues of bud scales on the tree, resulting in the production of conidia. The ascospores and conidia thus formed play an important role in the primary infections. The discharge of ascospores and the dispersal of conidia occur mainly in rainy periods. The incubation period of the fungus in leaves and fruit is influenced by weather conditions and is 3-4 weeks or even longer. The fungus repeats secondary infections several times a year. In the rainy season (June to July in Japan), the conidia are actively disseminated. In the hot summer, however, the fungus is usually inactive. In autumn, it becomes active again and new infection of buds occurs. The infection tends to last until the middle or late autumn in Japan.

For more information on the biology or physiology of the pathogen, see Yamamoto & Tanaka (1962; 1963), Tanaka & Yamamoto (1964), Misonou & Fukatsu (1970; 1971), Takanashi et al. (1970), Umemoto & Nagai (1985), Umemoto (1990, 1991a, 1991b), Eguchi & Yamagishi (2008), Asari (2016), and Ishii et al. (in press).

Symptoms

In early spring, bud scales infected the previous year develop and form conidia, which infect the basal portion of young clusters and produce black sporulating lesions. Subsequently, abundantly sporulating lesions can be observed on leaves, petioles, fruit and young shoots. Infections of petioles and peduncles result in premature abscission of leaves and fruit, respectively. Uneven development or cracking of the fruit occurs after infections. The quantity of conidia formed on leaves decrease after summer has passed.

Morphology

Conidia occur singly and are one-celled, pale-brown, ovate, but sometimes irregular in shape, 6.4-27.9 x 3.7-14.7 µm. Ascospores are unequally two-celled, with a septum near the base, pale-brown, 10.0-15.0 x 3.8-6.8 µm.

A full description is given by Tanaka & Yamamoto (1964), Ishii & Yanase (2000), Ishii et al. (2002), and Ishii et al. (in press).

Detection and inspection methods

Typical symptoms of scab may be observed on fruit. Host plants for planting at the dormant stage may carry the pathogen in the form of mycelia in the inner tissues of bud scales without showing any symptoms, thus, escaping detection via visual inspection (EFSA, 2017).

Based on a nucleotide sequence of the rDNA-ITS (ribosomal DNA-internal transcribed spacer) regions, a PCR (polymerase chain reaction) test was developed to identify V. nashicola (Le Cam et al., 2001; Zhao et al., 2016). For quarantine inspection of fruit, a real-time PCR test was also developed using a nucleotide sequence of the translation elongation factor-1 α gene (Yun et al., 2015).

Under natural conditions, V. nashicola spreads by conidia or ascospores within orchards. In international trade, V. nashicola is liable to be carried on infected plants for planting (with or without leaves) of the host Pyrus as well as on fresh fruit of host plants (EFSA, 2017; USDA, 2009).

Economic impact

In Eastern Asia, V. nashicola is one of the most serious pathogens in Pyrus pyrifolia var. culta, P. bretschneideri, and P. ussuriensis. The pathogen causes fruit drop, cracking, and malformation. A very small number of scab-resistant cultivars are commercially available, and these are all within the variety Pyrus pyrifolia var. culta (Ishii & Kimura 2018; Ishii et al. in press).

Control

Commercial orchards have been successfully protected by chemical spraying coupled with routine inspections, and removal of infected parts, and of pear leaves from the ground in particular, to reduce primary infection source. However, strains of V. nashicola resistant to benzimidazole (MBC) fungicides are widely distributed throughout Japan, making it difficult to control the disease with this group of fungicides (Ishii et al., 1985; Ishii, 2012). MBC resistance has also been found in the Republic of Korea (Kwak et al. 2017) and China (Ishii et al. 2009). Since 1986, sterol demethylation inhibitors (DMIs), such as triflumizole, bitertanol, fenarimol, hexaconazole, fenbuconazole, difenoconazole and others have been introduced into Japan for the control of pear scab, and have replaced benzimidazoles for this purpose. Subsequently, the pathogen developed resistance to DMIs as well (Kikuhara & Ishii, 2008; Ishii, 2012). DMI resistance has also been reported in the Republic of Korea (Kwon et al. 2010).

Phytosanitary risk

V. nashicola is undoubtedly of considerable economic importance on Asian pears, but its significance for the EPPO region is questionable now that it has been demonstrated that P. communis is not a host of V. nashicola. EFSA (2017) notes that the impact at the EU level is expected to be limited because Asian pears are not major crops in the EU but that the impacts of the pathogen to individual growers and enterprises could be significant. If the pathogen was introduced in the EPPO region, it could establish on Asian pears as the climate is likely to be suitable.

Phytosanitary measures, in particular for host plants for planting, may be justified in countries where Asian pears are important crops. Biosecurity New Zealand (2009) estimated that the likelihood of introduction of V. nashicola with fruit is low as the fungus could only spread from an infected fruit to an orchard if infected fruit is disposed underneath or in the immediate vicinity of a nashi tree or orchard. 

EFSA (2017) suggest the following mitigation methods to prevent the introduction of V. nashicola into the EU: host plants for planting (including plants at dormant stage) and fresh fruit should be imported from pest-free areas or pest-free places of production and inspected both at the place of origin and at the EU entry point. Biosecurity New Zealand (2009) and USDA (2009) recommend that fruit comes from a pest-free area or a pest-free place of productions, or that fruit lots are inspected for symptoms before export.

Asari M (2016) Venturia inaequalis, causal agent of apple scab, has lower tolerance than V. nashicola, causal agent of Japanese pear scab, for high temperature. Japanese Journal of Phytopathology 82, 185-191.

Biosecurity New Zealand (2009) Import Risk Analysis: Pears (Pyrus bretschneideri, Pyrus pyrifolia, and Pyrus sp. nr. communis) fresh fruit from China. 462 pp. https://www.mpi.govt.nz/dmsdocument/2884-Pears-Pyrus-bretschneideri-Pyrus-pyrifolia-and-Pyrus-sp.-nr.-communis-fresh-fruit-from-China-Final-Risk-Analysis-October-2009

Cho EK, Cho WT, Lee EJ (1985) The causal organism of pear scab in Korea. Korean Journal of Mycology 13, 263-265.

EFSA (2017), EFSA Panel on Plant Health, Jeger M, Bragard C, Caffier D, Candresse T, Chatzivassiliou E, Dehnen-Schmutz K, Gilioli G, Gregoire J-C, Jaques Miret JA, MacLeod A, Navajas Navarro Maria, Niere B, Parnell S, Potting R, Rafoss T, Urek G, Van Bruggen A, Van der Werf W, West J, Winter S, Gonzalez-Dominguez E, Vicent A, Vloutoglou I, Bottex B and Rossi V, Scientific Opinion on pest categorisation of Venturia nashicola. EFSA Journal 15(11), 5034, 22 pp. https://doi.org/10.2903/j.efsa.2017.5034

Eguchi N, Yamagishi N (2008) Ascospores of the Japanese pear scab fungus (Venturia nashicola Tanaka & Yamamoto) are discharged during the day. Journal of General Plant Pathology 74, 41-45.

Ishii H (2012) Resistance in Venturia nashicola to benzimidazoles and sterol demethylation inhibitors. In: Thind TS (ed) Fungicide Resistance in Crop Protection. CABI, Wallingford (GB), pp21-31.

Ishii H, Kimura Y (2018) A new interspecific pear cultivar Yutaka: highly resistant to the two major diseases scab and black spot on Asian pears. European Journal of Plant Pathology 152, 507-514.

Ishii H, Nishimura K, Tanabe K, Yamaoka Y (in press). Pathogenic specialization of Venturia nashicola, causal agent of Asian pear scab, and resistance of pear cultivars Kinchaku and Xiangli. Phytopathology, https://doi.org/10.1094/PHYTO-06-20-0220-R

Ishii H, Udagawa H, Yanase H, Yamaguchi A (1985) Resistance of Venturia nashicola to thiophanate-methyl and benomyl: build-up and decline of resistance in the field. Plant Pathology 34, 363-368.

Ishii H, Watanabe H, Tanabe K (2002) Venturia nashicola: pathological specialization on pears and control trial with resistance inducers. Acta Horticulturae 587, 613-621.

Ishii H, Yanase H (2000) Venturia nashicola, the scab fungus of Japanese and Chinese pears: a species distinct from V. pirina. Mycological Research 104, 755-759. https://doi.org/10.1017/S0953756299001720

Johnson S, Jones D, Thrimawithana AH, Deng CH, Bowen JK, Mesarich CH, Ishii H, Won K, Bus VGM, Plummer KM (2019) Whole genome sequence resource of the Asian pear scab pathogen, Venturia nashicola. Molecular Plant-Microbe Interactions 32, 1463-1467. https://doi.org/10.1094/MPMI-03-19-0067-A

Kikuhara K, Ishii H (2008) Fenarimol resistance in Venturia nashicola, the scab fungus of Japanese pear in Fukuoka Prefecture. Kyushu Plant Protection Research 54, 24-29.

Kwak Y, Min J, Song J, Kim M, Lee H, Kim HT (2017) Relationship of resistance to benzimidazole fungicides with mutation of β-tubulin gene in Venturia nashicola. Research in Plant Disease 23, 150-158.

Kwon SM, Yeo MI, Choi SH, Kim GW, Jun KJ, Uhm JY (2010) Reduced sensitivities of the pear scab fungus (Venturia nashicola) collected in Ulsan and Naju to five ergosterol-biosynthesis-inhibiting fungicides. Research in Plant Disease 16, 48-58.

Le Cam B, Devaux M, Parisi L (2001) Specific polymerase chain reaction identification of Venturia nashicola using internally transcribed spacer region in the ribosomal DNA. Phytopathology 91, 900-904.

Misonou T, Fukatsu R (1970) Studies on the infection and control of pear scab. II. Dispersion of conidia and their role as the origin of infection. Bulletin of the Chiba-ken Agricultural Experiment Station 10, 91-98.

Misonou T, Fukatsu R (1971) Studies on the infection and control of pear scab. III. The lesion types and sporulation of conidia on scales. Bulletin of the Chiba-ken Agricultural Experiment Station 11, 96-102.

Prokchorchik M, Won K, Lee Y, Segonzac C, Sohn KH (2020) Whole genome enabled phylogenetic and secretome analyses of two Venturia nashicola isolates. Plant Pathology Journal 36, 98-105.

Sivanesan A (1977) The taxonomy and pathology of Venturia species, pp. 94-99. J. Cramer, Vaduz, Liechtenstein.

Takanashi K, Yamamoto S, Kitajima H (1970) Primary inoculum of Japanese pear scab. Bulletin of the Horticultural Research Station, Japan A-9, 17-33.

Tanaka S, Yamamoto S (1964) Studies on pear scab. II. Taxonomy of the causal fungus of Japanese pear scab. Annals of the Phytopathological Society of Japan 29, 128-136.

USDA (2009) Importation of fresh fruit of Chinese sand pear, Pyrus pyrifolia, from China, including the special administrative regions of Hong Kong and Macau, into the entire United States, including all territories - a qualitative, pathway-initiated risk assessment. 76 pp. APHIS-2011-0007-0002. Available from https://beta.regulations.gov/document/APHIS-2011-0007-0002

Umemoto S (1990) Infection sources in Japanese pear scab (Venturia nashicola) and their significance in the primary infection. Annals of the Phytopathological Society of Japan 56, 658-664.

Umemoto S (1991a) Infection of bud scales with conidia of Japanese pear scab fungus, Venturia nashicola. Annals of the Phytopathological Society of Japan 57, 188-195.

Umemoto S (1991b) Relationship between leaf wetness period, temperature, and infection of Venturia nashicola to Japanese pear leaves. Annals of the Phytopathological Society of Japan 57, 212-218.

Umemoto S (1993) Studies on the ecology and control of Japanese pear scab.  Special Bulletin of the Chiba- Ken Agricultural Experiment Station 22, 1-99.

Umemoto S, Nagai Y (1985) The infection period of flower bud scales by Japanese pear scab fungus and effective fungicidal control method for scab during middle to late autumn. Bulletin of the Chiba-ken Agricultural Experiment Station 26, 129-135.

Yamamoto S, Tanaka S (1962) Studies on the pear scab (Venturia spp.). I. Cultural characteristics of the causal fungus with special reference to sporulation. Bulletin of the Horticultural Research Station, Japan B-1, 163-171.

Yamamoto S, Tanaka S (1963) Studies on the pear scab (Venturia spp.). III. Infection on the leaves by conidia. Bulletin of the Horticultural Research Station, Japan B-2, 181-192.

Yun YH, Yoon SK, Jung JS, Kim SH (2015) Specific and sensitive detection of the pear scab fungus Venturia nashicola by SYBR green real-time PCR. Journal of Microbiology and Biotechnology 25, 1782-1786. https://doi.org/10.4014/jmb.1507.07095

Zhao P, Kakishima M, Uzuhashi S, Ishii H (2012) Multigene phylogenetic analysis of inter- and intraspecific relationships in Venturia nashicola and V. pirina. European Journal of Plant Pathology 132, 245-258.

Zhao P, Yamada A, Kakishima M, Ishii H (2016) In planta expression profiles and sequence variation of the endopolygalacturonase gene in Venturia nashicola, the causal agent of Asian pear scab. Tropical Plant Pathology 41, 67-77. https://doi.org/10.1007/s40858-016-0069-5

This datasheet was extensively revised in 2020 by Hideo Ishii (University of Tsukuba, Japan). His valuable contribution is gratefully acknowledged.

EPPO (2024) Venturia nashicola. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-04-19)

This datasheet was first published in two editions of 'Quarantine Pests for Europe' in 1992 and 1997, and revised in 2020. It is now maintained in an electronic format in the EPPO Global Database. The sections on 'Identity', ‘Hosts’, and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.

CABI/EPPO (1992/1997) Quarantine Pests for Europe (1^st and 2^nd edition). CABI, Wallingford (GB).