Linaldeddu B T, Scanu B, Franceschini A
Dipartimento di Protezione delle Piante, Sezione di Patologia Vegetale, Università degli Studi di Sassari, Via E. De Nicola 9, 07100 Sassari, Italy.
Plant Dis. 2010 Jul;94(7):919. doi: 10.1094/PDIS-94-7-0919C.
Strawberry tree, family Ericaceae, is an evergreen shrub or small tree that grows in the Mediterranean Region. In spring 2009, a survey was conducted to study the fungi associated with canker and branch dieback of strawberry tree in a natural stand located on Caprera Island (41°12'N, 9°27'E), Italy. Fungal isolates obtained from live twigs and branches showing sunken necrotic bark lesions were identified as Diplodia scrobiculata J. de Wet, Slippers & M.J. Wingf. on the basis of morphological features (1). On potato dextrose agar (PDA) at 25°C, D. scrobiculata isolates developed white colonies with appressed mycelium that became dark gray after 4 to 6 days and formed pycnidia after 2 weeks on sterile Pinus radiata needles placed on the PDA surface. The conidia were dark brown with zero to three septa, clavate with truncate base, and measured 31.1 to 41.9 (36.8) × 11.3 to 16.3 (12.6) μm, with a length/width ratio of 2.9 ± 0.1 (mean ± standard error) (n = 50). Identity was confirmed by analysis of the internal transcribed spacer region (ITS1-5.8S-ITS2) of rDNA. BLAST searches in GenBank showed 100% similarity with reference sequences of D. scrobiculata (GenBank Nos. AY160200, EU220438, EU220444, and EU392283). The representative sequence of one D. scrobiculata strain (BL5), stored in the culture collection of the Department of Plant Protection at the University of Sassari, was deposited in GenBank (Accession No. GU722102). Pathogenicity of strain BL5 was tested by stem inoculation on eight 2-year-old strawberry tree seedlings maintained in a greenhouse at 18 to 26°C. A mycelial plug (3 to 4 mm) taken from the margin of an actively growing colony on PDA was put in a shallow wound (~3 mm) made by a scalpel on the basal part of the stem of each seedling. Four weeks after inoculation, the seedlings displayed dark brown-to-black discoloration, measuring 1.7 ± 0.6 cm (mean ± standard error) of the bark and wood tissues of the stems. The pathogen was successfully reisolated from symptomatic stem tissues, thus fulfilling Koch's postulates. Three control seedlings inoculated with sterile PDA plugs remained asymptomatic. These results demonstrate the active role played by D. scrobiculata in the aetiology of the canker and branch dieback observed on strawberry tree. D. scrobiculata is generally recognized as a weak pathogen of gymnosperms worldwide (2), however, it has recently been reported on olive in Italy (3). To our knowledge, this is the first report of D. scrobiculata on strawberry tree. Currently, further investigations are in progress to determine the possible role of biotic and abiotic factors in the development of this disease. References: (1) J. De Wet et al. Mycol. Res. 107:557, 2003. (2) J. De Wet et al. Mol. Phylogenet. Evol. 46:116, 2008. (3) C. Lazzizera et al. Fungal Divers. 31:63, 2008.
草莓树属于杜鹃花科，是一种生长在地中海地区的常绿灌木或小树。2009年春季，在意大利卡普雷拉岛（北纬41°12′，东经9°27′）的一片天然林分中，开展了一项调查，以研究与草莓树溃疡病和枝条枯死相关的真菌。从呈现凹陷坏死树皮病斑的活嫩枝和枝条上分离得到的真菌菌株，根据形态特征被鉴定为皱纹 Diplodia scrobiculata J. de Wet、Slippers & M.J. Wingf.（1）。在25°C的马铃薯葡萄糖琼脂（PDA）培养基上，D. scrobiculata菌株形成白色菌落，菌丝紧贴培养基，4至6天后变为深灰色，在置于PDA表面的无菌辐射松针上培养2周后形成分生孢子器。分生孢子深褐色，具0至3个隔膜，基部截形，棍棒状，大小为31.1至41.9（36.8）×11.3至16.3（12.6）μm，长宽比为2.9±0.1（平均值±标准误差）（n = 50）。通过对核糖体DNA的内部转录间隔区（ITS1-5.8S-ITS2）进行分析，确认了其身份。在GenBank中进行的BLAST搜索显示，与D. scrobiculata的参考序列（GenBank编号：AY160200、EU220438、EU220444和EU392283）具有100%的相似性。一个D. scrobiculata菌株（BL5）的代表性序列保存在萨萨里大学植物保护系的培养物保藏中心，并已存入GenBank（登录号：GU722102）。通过对8株在18至26°C温室中养护的2年生草莓树幼苗进行茎部接种，测试了菌株BL5的致病性。从PDA上活跃生长的菌落边缘切取一个菌丝块（3至4毫米），放入每株幼苗茎基部用手术刀造成的浅伤口（约3毫米）中。接种4周后，幼苗茎部的树皮和木质组织出现深褐色至黑色变色，病斑长度为1.7±0.6厘米（平均值±标准误差）。从有症状的茎组织中成功重新分离出病原菌，从而满足了柯赫氏法则。接种无菌PDA块的3株对照幼苗未出现症状。这些结果表明，D. scrobiculata在草莓树溃疡病和枝条枯死的病因学中发挥了积极作用。D. scrobiculata在全球范围内通常被认为是裸子植物的弱病原菌（2），然而最近在意大利的橄榄树上也有报道（3）。据我们所知，这是D. scrobiculata在草莓树上的首次报道。目前，正在进行进一步的调查，以确定生物和非生物因素在该病发生发展过程中可能发挥的作用。参考文献：（1）J. De Wet等人，《真菌研究》107:557，2003年。（2）J. De Wet等人，《分子系统发育与进化》46:116，2008年。（3）C. Lazzizera等人，《真菌多样性》31:63，2008年。
