Twig Die-Back of Tea Caused by Macrophoma theicola in Taiwan*

Transcription

1 Ei-fime\R53: (1987) Ann. Phytopa'th.Soc,Japan 53 : (1987) Twig Die-Back of Tea Caused by Macrophoma theicola in Taiwan* Jee-songCHEN**, Fang-ming THsENG** and Wen-hsiung Ko*** Abstract Dead twigs of unknown cause standing among healthy twigs with normal green Ieaves in the same bush of tea have been observed frequentlyin Taiwan since Jvfhcrophoma theicolawas isolated from 102 of 104 diseasedtwigs collected irom various cultivars at different locations, Three weeks after inoculation with wheat-oat grains colonized by Ml theieola,more than 86% of inoculated twigs showed die-backsymptoms similar to those observed in nature. Mkecrophoma theieola was reisolated from all of the experimentally infected twigs. All control twigs remained healthly during the experiment. Twigsinoculated with Ml theicolagrown en potato dextroseagar failedto show any dtsease symptoms. MLicrophoma theieola thrived at relatively hightemperature and endured low water potential,the fungus was able to grow about O,3cm Iinearlyin 2 days at 38 C and in5days at -71 bars. (ReceivedNovember 19, 1986) Key words : twig die-back, tea, M!zcrophoma theicola,taiwan. Introduction Tea (T7ieasinensis L.) is an irnportant agricultural crop in Taiwan, Its young shoots and tender leaves are dried and prepared for both export and local use to make the popular oriental beverageof ancient origin. In 1955 twig die-back of tea was noticed in central and northern Taiwan. The disease, which is rnost serious during the dry summer, caused the death of more than 40% of tea bushes in certain orchardsi2'. A similar diseasehas also been reported in Japan2'3'5'. Since 1959, a number of plant pathologistshave attempted to determine the cause of the diseasewithout success2'i2). Numerous fungi including Colletotrichum sp,, Pestalotia sp., Alectria sp,, Rhomopsis sp., Macrophoma sp. and Boti3,odiplodiasp, have been isolated frorndiseased tissues,but none of them caused the same disease in pathogenicity tests2''2).we report here evidence suggesting that MacrqPhoma theicola Petch is the causal organism of twig die-back ef tea in Taiwan, We also studied the effects of temperature and osmotic water potentialon the growth of the pathogen, * ***** Journal Series No of Hawaii Instituteof Tropical Agriculture and Human Resources. Supported in part by a grant from the National Scienee Council of the Republic of China (NSC B-06e-Ol). Taiwan Tea Experiment Station, Yangmei, Taoyuan, Taiwan 326,R.O. C, Department of Plant Pathology, Universityof Hawaii, Beaumont AgricultureResearch Center ' Hile,Hawaii 96720,USA.

2 Ann. Phytepath. Soc,Japan 53 (2). April, Materials and Methods ISotation Sections(about5-7rnm diam, and 5-10 mm long) ef infected twigs obtained from the advancing margin were washed with water containing a small amount of detergent to remove dusts,surface--sterilized by dipping in 75% ethanol for 2-3 min and 1% NaCIO for 10 min, and rinsed thrice with sterile distilledwater. Surface-sterilizedtwig sections were cut into small pieces (about3 3 7mm) and plated on 2% water agar. Pathegenicitu tests. The wheat-oat rnedium which rendered 1fretgschmariacgavus very effective in causing disease on branches and seedling stems of macadamia6"' was used to grow Macrophoma theicola(isolate No. 46) for pathogenicity tests. The fungus was grown on wheat-oat medium (10g whole wheat grains, 10 g whole oat grains and 10 ml distilled water) for7 days at 28 C. Tea twigs (2-3 or 5-7 mm diam.) of cv. Chinhsin Oolong were surface-disinfected with 75% ethanol and scraped gently to remove the epidermis from bark tissues. Four colonized grains were placed on the scraped portion of the twig, wrapped with Parafilm, and secured with vinyl tape. Twigs similarly'inoculated with autoclaved grains were used as controls. To deterrninethe time required for infectionof the host by the pathogen, the inoculum was rernoved after incubation for 3, 6, 9, 12, 15 and 21 days. Data were recorded 12, 15, 18 and 21 days after rernoval of the inoculum, Each treatrnentconsisted ef replicates, The path- done three times. ogenicity tests were Effect of ternperature and water potentiat. MacrQPhoma theicoga was grown on potato dextrose agar (PDA) at 28C for2 days. Agar discs (6 mrn diam,) cut from the periphery of the colony with a sterile cork borer were used to inoculateagar plates. To deterrninethe effect of temperature on growth of the pathogen, inoculated PDA plates were incubatedat 12,16, 20, 24, 28, 32, 34,36 and 38 C, and colonies were measured after 2 days. To determinethe effect of water potential on the growth of the pathogen, various amounts of KCI were added to a basal medium consisting of O.75 g of Na2HP04, O.75 g of KH2P04, O.12 g of NaCl, O,4g of NH4N03, 1,8g of glucose, O.1g of yeast extract, 1,O g of malt extract, and 15 g of agar per 1,OOO ml of distilledwaterio'i". Inoculated plates of basal mediurn with theoreticalwater potentials of -1, -9, -22, -35, --53,-71 and -90 bars were incubated at 24 and 32 C. Colonieswere measured after 5 days, Five replicates were used for each treatment and experirnents were done three times. Results Sgmptoms The common sight of tea twig die-back observed in the fieldis one or more dead twigs with or without brown leaves standing arnong livingtwigs with normal green leaves in the same bush. In an early stage of the disease development, leavesof the affected young shoot turn lightgreen and lesevigor. These are followed by browning and with-

3 200 HJ]FidiimtiPi-\ft--vaee53igeg2ig'HaliU62ge4E Table 1, Relationbetween inocu]ationtime and development of tea twig die-back caused by MdecroPhoinatheicola(isolate No. 46) Inoculation tirne (days) Disease incidence (%) after (days) o o o o e,ring of the whole shoots and abscission of dead leaves. Browning frequently occurs on veins beforethe other parts of leaves turn brown. During the dry hot season, a shoot may appear light green in the morning, but drooping by noon. Affected branches turn brown and die gradually downwards. It may be several years before the disease reaches the crown and killsthe whole bush. In some cases the disease appears as cankers with elongated dark patches on the wood of branches surrounded by callus. Pathogenicity In 1983,a fungus identifiedas Macrophoma theicolapetchs'"'by Dr.R, A, Samson of Centraalbureau voor Sehimmelcultures was isolated from 46 of 48 diseased tea twigs on -12 different cultivars at 15 different tea production areas on the island of Taiwan. In 1984,M. theicola was isolatedfrom all 56 diseased tea twigs on 6 cultivars at 17 locations. Three weeks after inqculationwith wheat and oat grains colonized by ML theicola,26 of 3e inoculatedtwigs showed symptoms similar to those observed in nature. Macrophoma theicolawas reisolated from all the experimentally infected twigs. The 30 control twigs remained healthy during the experiment. Twenty nine tea twigs similarly inoculated with Ml theieoga grown on potato dextrose agar also failedto shew any diseasesymptoms, When inoculum was removed at differentime intervals,itwas found that more than 3 days were needed for successful infectionof ML theicolaon tea twigs CTable1). None of the inoculatedtwigs developed die-back symptoms when the inoculum was removed on the third day, The diseaseincidenceincreased with increasing time of inocu]ation to a maximum at about 9-12 days. Effeet of temperature and water potentiat on ntycelial grototh Macrophoma theicolaappeared to thrive at relatively hightemperature (Fig, 1). The optimum temperature for the growth of this fungus was 28 to 34 C. Even at 38 C the fungus was able to grow about O.3cm linearlyin two days, The fungus did not grew at 12 C. Macrophoma theicolawas able to grow on basal medium at relatively low water potential caused by addition of KCI (Fig.2). The fungus showed sparse growth at -90 bars and grew about O.3cm linearly at -71 bars in 5 days at 32 and 24 C. The optimum water potential forgrowth of M. theicolawas -1 bar at 32 Cand -9 bars at 24 C.

4 Ann,.Phy!o. pgth,..s.p/gl..llp.ani.g (2)Ạpril, Eovorw-wE(-o'Zo"oo 6 4 Fig. 1.Growth of MdcroPho"za theicola (isolate No. 46) on potato dextrose a- gar for 2 days at different temperatures. 2 o TEMPERATURE ( C ) AEow 6 crwhure(a'zo=oo 4 2 o O WATER POTENTIAL <-BAR} Fig.2, Growth of MacroPhoma theicola Cisolate No. 46) on basal medium at differentwater potentials caused by addition of KCI at 24 and 32 C for 5 days. Discussion Numerous unsuccessful attempts have been made by plant pathologists in Taiwan and Japan to deterrnine the cause of twig die-back of tea since 19572'i2'.In this study, M, theicolawhich was consistently isolatedfrom tea twigs with die-back sympterns was found to be responsible for incitingthe disease.upon inoculationoi healthy twigs of tea,m. theicolacaused symptoms ef die-back similar to those occurrlng in nature, and the fungus was reisolated from all experimentally infected twigs. Although ML theicolahas been considered to be the causal agent of twig die-backof tea in Japan since 1931i',previous atternpts to prove pathogenicitywith Macrophoma sp,, presumably ML theicola,isolatedfrorndiseased tissues had not been successfu12'i2). This was probably due to the usage of unsuitable rnedia for growing the fungus. Our results showed that AdLtheicolawas pathogenic to tea plants when grown in wheat-oat medium, but not when grown in potato dextroseagar. Virulenceof several plant pathogenic fungi, including Rhixoctonia solani and Rythium zaltimum, also has been shown to be affected by exogenous nutrients`'i`'. The substance in the wheat-oat medium which

5 The Phytopathologioal Phytopathological Society Sooiety of Japan 202 日木植物病理学会報第 53 巻第 2 号昭和 62 年 4 月 is responsible for the virulence of M.theicolaremains to be detefmined. The observation that twig die back of tea was most serious d ご ring the dry summer appears to result from the combination of the ability Qf 丑 4.theicolα to tolerate high temperature and low water potential and the stress suffered by tea plants under hot and dry conditions which may render the host more susceptible to the pathogen. 1 晦ご roi ) ん o 珊 α theicolahas been reported to cause main! y cankers of tea twigs in othef regions13 >. This may be due to the differencesin environmental conditions and varieties of tea plants existing in those areas. Literature cited Hara,K.(1931).The Disease of Tea Bush ( in Japanese). pp, Hirokawa,S.and Takaya,S. (/964).Tea Res.J,22 : Hirokawa,S.,Takaya,S.and Kibushi,H. ( 1964).Tea Res. 丁.22 : Johnson,L.F.,Hsieh,C.C.and Sutherland,E.D.(198ユ).Phytopathology 71 : Kasai,K.,Hirokawa,S,Takaya,S.and Kibushi,H. ( 1965 ).Tea Res.J.23 : Ko,W H.and Kunimoto,R.K.(/986),Ann.Phytopath.Soc. apan 52.: , Ko W H Tomita,J and Short,R L ( 1986).PlantPatho1.35 :254 一獅. Petch,T. ( 1917 ). Description of the New CeylorlFungi.Ann.Roy.Bot.Gard.,Peradeniya 7,pp. 1 一ユ 0, ( ン Petch,T. ( 1923). The Diseasesof Tea Bush,Macmillan and Co,London,pp Roblnson,R.A.and Stokes.R.H. ( 1955 ).Electrolyte Solutions,Academic Press,New York, PP , Sommers,L.E.,Harris, R.F., Dalton,F.N.and Gardner,W,R, ( 1970).Phytopathology 60 : Wang,L.C. ( 1983).Taiwan Tea Res.Bull.2 :62 7ユ. 13. Weber,G.F. ( /973).Bacterialand Fungal Diseases of Plantsin tlletropics.universityof Florida Press,Gainesville,Florida,pp, Weinhbld,A.R.,Rodman,R,L.and Bowman,T. ( ユ972).Phytopathology62 ; 和文摘要 Jee song CHEN Fang ming THsENG Wen hsiung Ko : 台湾における Macrqphema theicola による茶樹 の川司枯病 台湾では /955 年以来, 茶樹において健全枝に混じって原因不明の枯死枝がしばしば観察されてきた 異なる. 産地の秬々の品種から収集した 104 本の罹病枝のうち 102 本から.M.theicola 力雪分離された コムギ. 一エンバク培地で生育させた M.theicola を接種した場合,3 週聞後には 86% 以上の接種枝で自然病徴と類似の胴枯症状 が再現され, またすぺての感染枝から lld.theicola が再分禽 ltされた オートクレープした菌および PDA. 培地で生育させた 1 司菌を接種した場合にはいずれも無病徴で健全のままであたっ M,theicola は比較 Vl 勺高温下で生育良好であり, また低い水ポテンシャルでも生育可能で,38C および一 71 バールではそれぞれ 2 凵および 5 口で約 0.3cm の菌糸の伸長が認められた NII-Electronic N 工工一 Eleotronio Library Service