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Since About 1966, a Phomopsis Different from the Citrus Melanose Ftmgus, Which Had Tentatively Been Identified As Diaporthe Citr

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Since About 1966, a Phomopsis Different from the Citrus Melanose Ftmgus, Which Had Tentatively Been Identified As Diaporthe Citr 日 植 病 報 42: 56-59 (1976) 短 報 Ann. Phytopath. Soc. Japan 42: 56-59 (1976) Phytopathological Note A Species of Diaporthe Pathogenic to Citrus Hirokuni YAMATO* 大和 浩 国＊:カ ンキ ツに病原性を有す るDiapotrhe属 菌 の一種 Since about 1966,a Phomopsis differentfrom the citrus melanose ftmgus, which had tentativelybeen identifiedas Diaporthe citriWolf1,2), has been known as the causal organism of a melanose-likeblemish on fruitsof Satsuma mandarin (Citrus Marc.)3). The symptom is representedby very minute, dark brown to purplish brown dots,0.02-0.08mm in diameter,which often form reticulatepatterns around oil vesicleson the peel, and is clearly differentiatedfrom citrus melanose symptoms which consistof distinctdark brown to black spots,0.1-0.5mm in diameter,and tear- stained or mud-caked patterns. Later, the fungus is known to be capable of causing stem-end rots of some citrusvarieties. In June 1969, a speciesof Diaporthe was found on dead twigs and branches of Satsuma mandarin and Hassaku (Citrus hassaku Tanaka)in orchards in Tokushima Prefecture.Cultural characters of the Diaporthe were qulte similar to those of the Phomopsis mentioned above. Size and shape of conidia of the former on agar media and on sterilizedtwigs were also identicalwith those of the latter.Ascospores and alpha conidia of the Diaporthe are somewhat shorterand narrower than corresponding spores of citrusmelanose fungus (Fig.1). Inoculation for comparing the pathogenicity of the Diaporthe sp. and the Phomopsis sp. was carried out in November, 1971. Mature fruits of Satsuma mandarin and Yuzu (Citrus junos Sieb. ex Tanaka) were inoculated respectively with two alpha conidial suspensions, one of which was ob- tained from ascospore and the other from conidium, and were incubated in a moist chamber at 25C. After 5 days or more incubation, minute dark brown spots, usually hardly visible to naked eye, Figure 1. Histograms of width and length were produced on fruits inoculated with Diaporthe of ascospores and alpha conidia of Diaporthe sp. and Diaporthe sp. and Phomopsis sp., respectively. These fruits citri. showed symptoms of stem-end rots after 4 weeks or more. These isolates required a longer incubation period for the disease development comparing with those of citrus melanose fungus which developed typical melanose *Tokushima Horticultural Experiment Station, Katsuura, Tokushima, Japan. 徳島県果樹試験場 1) Yamato, H. (1971), Ann. Phytopath. Soc. Japan 37: 355-356. 2) Ushiyama, K. (1973). Ibid. 39: 120-126. 3) Ushiyama, K. and Kuramoto, T. (1975). Shokubutsu-boeki (Plant Protection) 29: 283-287. Ann. Phytopath. Soc. Japan 42 (1). January, 1976 57 symptoms 2 days and stem-end rots 2 weeks after inoculation respectively. Isolates having similar cultural characters as those used for inoculation were reisolated from each of the rotted fruits. Inoculation to stems of young Satsuma man- darin, Ponkan (Citrus poonensis Hort.) and sour orange (Citrus aurantium L.), wounded with a hot iron, showed that both isolates of the Diaporthe and the Phomo- psis were able to slightly invade healthy stem tissues of citrus. Based on their similar pathogenicity to citrus, cultural characteristics and morphology of alpha and beta conidia, the Diaporthe sp. newly found in citrus orchards is cosidered to be the perfect stage of the Phomopsis sp. causing melanose-like blemishes of citrus fruits. Morphology of the Diaporthe under consideration is as follows: Diaporthe stage- perithecia embedded within bark tissue and partly in wood, single or in a small group, globular, 250 to 800ƒÊm in diam., with a long neck erumpent singly or in a cluster, 3 to 7mm in length under moist conditions; asci elongate-clavate, with an apical ring, 8-spored, 38-58•~7-10ƒÊm, avg. 48.1•~8.5ƒÊm; ascospores elongate-elliptic to f usoid, hyaline, uniseptate, constricted at the septum, usually 4 guttulate, 9-14.5•~2.3-4.5ƒÊm, avg. 11.6•~3.1ƒÊm; paraphyses absent. Phompsis stage-pycnidia beneath the epidermis of bark, ovoid, with an erumpent ostiole, 150 to 500ƒÊm in diam.; alpha conidia elongate- ovate to fusoid, hyaline, unicellular, feebly biguttulate, 5-9•~1.5-3ƒÊm, avg. 7.0•~2.1ƒÊm; beta conidia filiform, hooked or curved, hyaline, unicellular, 17-36•~0.7-1.5ƒÊm, avg. 27.4•~1.0ƒÊm. Combination culture tests with four isolates of the Phomopsis sp. causing melanose- like blemishes, which had been isolated from Satsuma mandarin and Yuzu, were conducted in October, 1971. After 5 months' incubation, mature perithecia were formed in four out of six combination cultures between the isolates of Phomopsis sp., while all of the eight combination cultures between the present Phomopsis sp. and Diaporthe citri failed to form the perfect stage. Morphology of perithecia) stage formed on the combination cultures between the Table 1. Formation of perithecial stage in combin- ation cultures on citrus twig media. different isolates of Phomopsis sp. was identical with the Diaporthe sp. found in field. It should be emphasized that the Diaporthe sp. investigated in this paper is clearly differenciated from the citrus melanose fungus which has been identified as Diaporthe *Phomopsis sp . I: isolated from Satsuma mandarin citri Wolf, with regard to the twig. sizes of ascospores and alpha con- Phomopsis sp. II-IV: isolated from stem-end rotted idia, symptoms on citrus fruits, fruits of Yuzu pathogenicity to citrus, cultural Diaporthe citri I-II: isolated from Diaporthe stage characters and mating compatibil- on Satsuma mandarin twigs. ity. Morphology of the Diaporte sp. under consideration quite agrees with the general concept of Diaporthe medusaea Nit., a species having wide host range4,5). Besides this 4) Wehmeyer, L.E. (1933). The genus Diaporthe Nitschke and its segregates: Univ. Mic. Press. pp. 349. 5) Kobayashi, T. (1970). Bull. Gov. For. Exp. Sta. 226 pp. 242. 58 日本植 物 病 理 学 会 報 第42巻 第1号 昭和51年1月 Diaporthe, the author have collected some specimens of Diaporthe on poplars (Populus spp.), Japanese pear (Pyrus serotina Rehder), European pear (Pyrus communis var. sativa L.) and apple (Malus pumila Mill. var. domestica Schneider), and all of them were similar to the Diaporthe under consideration in morphology and pathogenicity to citrus. They seem to be included in the concept of Diaporthe medusaea sensu Weh- meyer. Although Wehmeyer treated Diaporthe citri Wolf as a synonym of Diaporthe medusaea Nit., the author believes that Diaporthe citri causing citrus melanose should be separated from Diaporthe medusaea Nit. It is concluded that the author's Diaporthe is very similar to Diaporthe medusaea Nit., but not to Diaporthe citri Wolf. (Received May 30, 1975) Explanation of plate 1-8. Diaporthe sp., 9-10. Diaporthe sp. and Diaporthe eitri. 1. Perithecial necks on Satsuma mandarin twig. 2. Perithecia within the bark tissue of Satsuma mandarin: scale line is 500ƒÊm. 3. Feature of Diaporthe stage formed in combination culture: perithecia are formed at the junction line of both isolates. 4. Asci developing on adhering tissue: scale line is 20ƒÊm. 5. Ascus and ascospores: scale line is 10ƒÊm. 6. Typical pycnidial ostioles showing characteristic feature of being strongly erumpent on citrus twig media. 7. Alpha conidia: scale is the same as fig. 5 in plate. 8. Pycnidial pustules on a stem-end rotted Satsuma mandarin fruit. 9. Mycelial colonies in culture: the Diaporthe sp. (left) grows faster than D. citri (right). 10. Melanose-like blemish caused by Diaporthe sp. (left) and typical melanose due to D. citri (right). Ann. Phytopath. Soc. Japan 42 (1) January, 1976 59.
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