林木病原菌的傳播途徑概述

陳帥飛

(國家林業(yè)局桉樹研究開發(fā)中心，廣東 湛江 524022)

林木病原菌的傳播途徑概述

陳帥飛

(國家林業(yè)局桉樹研究開發(fā)中心，廣東 湛江 524022)

病原菌隔離在林木分布區(qū)域之外是避免病原菌對林木危害的關鍵措施之一，這可以通過控制病原菌的傳播來實現(xiàn)。病原菌的傳播途徑主要包括土壤/苗木基質、植物體材料、木材/木材制品、昆蟲以及空氣等。本文對林木病原菌的以上傳播途徑進行了簡要概述。

林木病原菌；病原菌傳播；檢驗檢疫；病害防控

控制桉樹病原菌的傳播對桉樹人工林的健康發(fā)展具有重要意義。自桉樹被引種到非本土生區(qū)域后，新的病原菌在新的桉樹種植區(qū)域不斷被發(fā)現(xiàn)[3-4,15]。近來，陳帥飛等[16-17]通過對我國 Teratosphaeria莖干斑點潰瘍病病原菌 Teratosphaeria zuluensis的種群多樣性研究發(fā)現(xiàn)，同一基因型的T. zuluensis在廣東湛江和廣西崇左/河池地區(qū)被發(fā)現(xiàn)，這表明T. zuluensis可能已經在兩個地區(qū)之間進行傳播。

林木病原菌的傳播途徑/介質包括土壤/育苗基質、植物體材料、木材/木材制品、林業(yè)生產設施/工具、昆蟲以及空氣等。本文對林木病原菌的傳播途徑進行簡要介紹。

1 林木病原菌的傳播途徑

1.1 土壤和育苗基質

土生植物病原菌可以隨著土壤和基質的轉運而傳播[1,3,18]，土生植物病原菌可以產生休眠結構，可以在土壤中存活很長時間[1,18]，比如厚垣孢子，在合適的條件下可以萌發(fā)、繁殖并侵染植物體。土壤/病原菌可以伴隨植物體、育苗設備等的轉運而廣泛傳播。

土生植物病原菌隨著轉運的土壤/基質與苗圃苗木一起傳播的情況十分普遍，這種方式是植物病原菌在不同地域之間傳播的一個主要途徑[19-20]。人工林的菌根真菌(mycorrhizal fungi)被證明可以通過土壤的轉運在世界范圍內傳播[19,21-22]，許多文獻中報道過 Armillaria spp.真菌隨著盆栽植物在世界各大洲之間傳播[23-24]。松樹(Pinus)根部病原菌Rhizina undulata是一種本土生于北半球的被廣泛研究的森林土生病原菌[25]，研究表明此病原菌很有可能是通過土壤被傳播到許多新的非病原菌本土生區(qū)域內，包括南半球的一些國家[3]。

許多桉樹苗圃病原菌通過土壤或育苗基質被傳播到新的區(qū)域，例如Botrytis cinerea，Calonectria spp.，F(xiàn)usarium spp.，Phytophthora spp.和Pythium spp.[1]。Ralstonia solanacearum是一種土生的具有廣泛寄主的細菌病原，它可以引起青枯病細菌枯萎病[18]。此病原菌也是世界范圍內桉樹的一類重大病原[26-27]，R. solanacearum對我國桉樹人工林造成了很大的危害[28-29]，研究表明此病原菌可以與土壤一起被動物攜帶，進而在不同地域之間傳播[26]。

1.2 植物體材料

植物體材料被認為是植物病原菌傳播的最普遍媒介之一[1,3-4,15,27]，植物體材料包括無性繁殖的樹木、幼苗、種子和花粉等[4,27,30]。許多病原菌伴隨著植物體材料在世界范圍內被廣泛傳播[20,31]。特別是一些造林類、園藝類和綠化類苗木，這些植物體材料常被轉運到新的區(qū)域，世界范圍內植物體材料的頻繁轉運加速了植物體上攜帶的病原菌在不同地域的傳播[15]。

由細菌引起的植物體枯萎病病原菌 Ralstonia solanacearum可以給苗圃里的桉樹苗帶來很大的危害[1,26-27]。苗圃里攜帶有R. solanacearum病原菌的幼苗被認為是南非桉樹人工林細菌枯萎病病原菌的一個主要來源[26]。由于R. solanacearum具有廣泛的寄主，它很容易通過感病的林木幼苗或者農作物傳播到新的人工林區(qū)域[32]。

內生真菌在植物體內不容易被監(jiān)測但很容易被傳播[8,33]。例如Botryosphaeriaceae是一個物種多樣性很高的科，具有廣泛的寄主，其中也包括桉樹[8]。研究表明Botryosphaeriaceae包含有很多內生性或潛伏性病原菌，它們常常潛伏在植物體內而并不引起感病癥狀的發(fā)生[8]。近來的一些研究證明Botryosphaeriaceae很有可能通過植物體材料在世界范圍內進行傳播[8]，比如Neofusicoccum eucalypticola以及N. eucalyptorum，它們可能本土生于澳大利亞的桉樹上，通過病原菌的寄主(植物體材料)傳播到智利和南非[34]?？傮w來說，現(xiàn)行的檢驗檢疫措施可能并不能及時發(fā)現(xiàn)潛伏性病原菌[8]，這些病原菌潛伏在表觀健康的植物體內部，在相當長一段時間內并不引起植物體感病癥狀的發(fā)生，而一旦植物體受到外界環(huán)境的脅迫或者處在自身生理調控的某些階段，潛伏性的病原菌就可能發(fā)作而引起病害。

松樹病原菌Diplodia pinea(Botryosphaeriaceae)可以隨著植物體材料而被傳播，如今D. pinea被發(fā)現(xiàn)分布于世界范圍內不同地區(qū)[8,35]。D. pinea常常內生于松樹內，一般通過本土生的松樹而傳播到其他松樹種植區(qū)域[35]。松樹在南非和澳大利亞是一種被廣泛種植的外來樹種，在非起源地南非，D. pinea病原菌的種群多樣性很高，這是因為南非的松樹來源于不同區(qū)域，D. pinea隨松樹一起從多個起源地域頻繁地傳播到南非[35-36]。針對D. pinea的種群多樣性研究發(fā)現(xiàn)，南非D. pinea的一些基因型也同時分布于澳大利亞和新西蘭，這進一步反映出 D. pinea在不同地域之間傳播的可能性[35]。

Chrysoporthe deuterocubensis和 Chr. cubensis是桉樹的重要病原菌之一，分別被發(fā)現(xiàn)于南半球的一些本土生的 Melostomataceae、Lythraceae和Myrtales植物上[37-39]，這些病原菌很可能起源于南半球的本土生植物[38-39]。Chrysoporthe deuterocubensis和Chr. cubensis均被發(fā)現(xiàn)于非洲，它們可能通過園藝類植物(例如 Tibouchina spp.)或產香料制品植物(Syzygium aromaticum)傳播到非洲的桉樹種植區(qū)域，并危及桉樹[37-39]。

據報道，有一些病原菌被發(fā)現(xiàn)于樹木的種子上，例如Acremomium spp.[40]、Aspergillus spp.[41]、Coniella spp.[40,42]、Cylindrocladium spp.[43]、Fusarium spp.[44]、Pilidiella spp.[40,42]以及Puccinia psidii[27]。利用基于PCR的DNA診斷技術，在巴西桉樹種植園的種子上發(fā)現(xiàn)了桉樹銹病病原菌P. psidii，而這些種子作為商品在世界范圍內流通[27]。Cylindrocladium (Calonectria)和Fusarium屬真菌包含一些重要的苗圃病原菌，它們可以降低種子的萌芽率或者引起種子萌發(fā)后的病害，例如猝倒病、葉枯病、炭疽病和莖潰瘍。Cylindrocladium(Calonectria)和 Fusarium可以附著在種子表面，并隨著種子被傳播[41,43,45-46]。

桉樹葉枯病和葉斑病病原菌Teratosphaeriaceae和 Mycosphaerellaceae科真菌常常發(fā)現(xiàn)于桉樹人工林種植的初期[3,47]，這表明這些葉部病原菌很有可能從澳大利亞通過植物體材料特別是種子傳播到新的區(qū)域[1,48-50]。

Quambalaria屬病原菌可以引起桉樹葉和頂梢枯萎。由于Quambalaria屬病原菌廣泛分布于澳大利亞[51]，且此類病原菌在很早以前就在該地區(qū)被發(fā)現(xiàn)，因此研究認為澳大利亞是桉樹Quambalaria屬病原菌的起源中心。Quambalaria被認為通過種子貿易由澳大利亞傳播到其他區(qū)域[51]。澳大利亞與其他國家頻繁的種子貿易加速了Quambalaria屬病原菌在世界范圍內的傳播[51]。

1.3 木材及木材制品

木材及木材制品的轉運是世界范圍內林木病原菌以及害蟲的主要傳播途徑[15,22,52-53]。Ophiostomatoid和 Botryosphaeriaceae真菌都可隨著木材的轉運而在全球范圍內傳播[3,8-9]。Ceratocystis和Ophiostoma常常存在于樹皮以及潛藏在木材中昆蟲的四肢上[3,9,54]，這些病原菌可隨著木材/昆蟲進行遠距離的傳播。

Amylostereum areoltum 是一種與木蜂 Sirex noctilio共生的木材腐朽病菌[55]。S. noctilio/A. areoltum共生體可以對某些針葉樹帶來很大的危害，比如松樹和云杉(Picea asperata)[55]。在過去的100 a間，S. noctilio/A. areoltum共生體被頻繁地從北半球傳播到南半球[3]。在非洲，S. noctilio最早于1962年發(fā)現(xiàn)于南非Port Elizabeth的一個貯存進口木材的場地內[56]，此后，S. noctilio通過被侵害的樹木和木材從南非南部的開普省傳播到北方的普木蘭咖省[57]。

控制攜帶有病原菌的木材及木材制品的轉運對控制病原菌的傳播十分必要。目前已經頒布了一些國際法規(guī)來減少病原菌通過木材或木材制品在各大洲之間的傳播[58]，比如在國際物流系統(tǒng)中只有除去樹皮的木材才被允許轉運。另外，國際上相關政策規(guī)定在木材轉運之前必須采取相應的處理措施來避免病原菌隨著木材被傳播[52,58]。

1.4 昆蟲

許多昆蟲已經適應隨著木材或木材制品進行遠距離傳播的不良環(huán)境，特別是沒有經過特定處理的或者沒有去皮的木材[2,59]。一些樹木真菌病原菌與昆蟲具有緊密的關系[9,60-63]。如 Ceratocystis和Ophiostoma真菌，它們與一些昆蟲共生，特別是Coleopteran屬的昆蟲，包括樹皮甲蟲、豚草甲蟲和露尾蟲等，這類真菌很容易隨著昆蟲進行傳播，特別是當昆蟲隨著木材或木材制品在全球范圍內轉運期間[60-62]。

在森林里，Ceratocystis菌和一些 Ophiostoma菌主要依靠昆蟲來傳播。Ceratocystis菌，特別是在Ceratocystis fimbriata多物種組合體里面的一些真菌，主要通過傷口來感染樹木[9,61,63]，這些真菌在樹木傷口的表面產生帶有芳香氣味的孢子來吸引昆蟲，昆蟲進而攜帶真菌的孢子到新的樹木傷口上去吮吸樹葉，從而把真菌從一棵樹木的傷口傳播到另一棵樹木的傷口[9,61]。

1.5 空氣

植物病原菌可以在空氣中通過氣流和風來傳播[64-66]。例如，銹病病原菌可以通過氣流長距離的傳播并存活下來[65-67]，這是因為銹菌的孢子壁很厚，可以抵抗氣流運動中強輻射和干燥條件帶來的損傷[68]。研究表明咖啡葉銹病的病原 Hemileia vastatrix可能是靠氣流和風從安哥拉傳播到巴西[69]。

桉樹銹病病原菌Puccinia psidii本土生于中南美洲的Myrtaceae上[70]，研究表明桉樹銹病病原菌可以通過風傳播到很遠距離的區(qū)域[68]，P. psidii一旦通過風傳播到新的區(qū)域，很快可以通過氣流進一步傳播[71]。

子囊菌很容易通過風在短距離內進行傳播，很多子囊菌的子囊孢子從子囊散布于空氣中后被傳播[72-74]。Teratosphaeria nubilosa的子囊孢子可以通過風傳播到寄主葉片上，并進行感染[75]。病原菌靠風進行傳播雖然速度比較慢，距離比較短，但足以引起病原菌在相鄰區(qū)域之間的擴散。

2 結語

近年來，世界范圍內在林木上發(fā)現(xiàn)的新病原菌越來越多[4,8,15,20,53]，這給林木病害的防控帶來了新的壓力。很多區(qū)域的病原菌來源于本區(qū)域之外，所以控制病原菌的傳播對林木病害的防控具有重要意義。

本文對林木病原菌的主要傳播途徑，包括土壤/苗木基質、植物體材料、木材/木材制品、昆蟲以及空氣等進行了簡要概述。在這些傳播途徑中，某些傳播途徑是無法或者很難人為干預，如昆蟲與空氣；而土壤/苗木基質、植物體材料、木材/木材制品等因素，完全可以通過人為措施來控制病原菌的傳播。

人類活動在林木病原菌的傳播過程中扮演了重要的角色，是許多病原菌傳播途徑的源動力[10-11,13,15,53,76]。過去一個世紀，人類活動引起了植物體材料、木材以及木材制品的廣泛傳播[3,10-11,15,31,76]。伴隨著世界范圍內貿易和國際間人員流動的日益頻繁，林木病原菌的傳播速度和頻率將繼續(xù)加快。因此，要強化控制林木病原菌通過人為因素而進行傳播的意識，并對林木病原菌引起的林木病害進行及時的監(jiān)測和診斷，進而建立嚴格的檢驗檢疫措施來有效地阻止或減緩病原菌的傳播速度，這對林木病害的防控具有重要意義。

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Summary of Forestry Tree Pathogen Pathways

CHEN Shuai-fei
(China Eucalypt Research Centre, Zhanjiang 524022, Guangdong, China)

The first line of defense against the spread of disease is the exclusion of potential damaging pathogens. This can be achieved by controlling the movement of pathogens into disease-free areas from a bio-geographical area(s) in which the pathogen(s) occur. Common pathways by which pathogens move include movement of soil/grow th media, germplasm, wood and wood products, air and/or insects. In this paper, the key pathways for movement of forestry pathogens are summarized.

forestry tree pathogen; pathogen pathway; inspection and quarantine; disease control

避免林木受病原菌的侵染是林木病害防控的一項關鍵措施[1]，這可以通過避免或控制特定病原菌從林木感病區(qū)域傳播到無相關病原菌區(qū)域來實現(xiàn)。林木病原菌的來源有兩個途徑，一個為病原菌起源于林木所在區(qū)域(本土生病原菌)，另一個為病原菌從其他區(qū)域傳播到當前林木所在區(qū)域(非本土生病原菌—外來病原菌)。無論本土生病原菌還是外來病原菌，控制它們的傳播對于病害的防控都十分必要。嚴格的檢驗檢疫措施可以有效地避免或阻止病原菌的傳播[2-9]。在世界范圍內，桉樹(Eucalyptus)被廣泛種植于非本土生區(qū)域，為避免本土生的病原菌傳播到其他區(qū)域，檢驗檢疫措施對桉樹病害的防控尤其重要[1,4]。
隨著世界貿易和人員流動的日益頻繁，過去幾十年內，被傳播的植物病原菌日益增多，植物病原菌的傳播速度也日益加快[7,10-13]。了解林木病原菌的傳播途徑不僅有助于指導檢驗檢疫的實施，還能有目的性地控制病原菌在不同地域的傳播，這對林木病害的綜合防控具有重要意義[14]。

S432.1

A

2014-05-15

廣東省林業(yè)科技創(chuàng)新專項“桉樹重大病蟲害控制技術研究與示范”(2010KJCX015-03)；國家國際科技合作專項項目“重要林業(yè)病

害致病力及多樣性研究”(2012DFG31830)

陳帥飛(1982— )，男，博士，副研究員，主要從事森林病害研究.E-mail:cerccsf@126.com