Pérez-Sierra A, Álvarez L A, León M, Abad-Campos P, Armengol J, García-Jiménez J
Instituto Agroforestal Mediterráneo, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain.
Plant Dis. 2007 Aug;91(8):1057. doi: 10.1094/PDIS-91-8-1057C.
Callistemons (Callistemon citrinus (Curtis) Skeels), evergreen plants of the family Myrtaceae, are commonly grown in Mediterranean gardens for their red bottlebrush-like flowers. During November of 2006, 1-year-old potted plants of callistemon showed leaf spots and blight in commercial nurseries in Valencia, Spain. Symptoms consisted initially of minute brown spots on the leaves, developing into black-gray blotches that finally coalesced. Diseased plants also showed stem lesions and blight of young shoots. Approximately 30% of the plants were affected. A Cylindrocladium sp. was isolated consistently from the infected tissues. Six single conidial isolates were grown on carnation leaf agar (CLA) under near-UV light at 25°C for 7 days (1). The macroconidiophores comprised of a stipe, a sterile elongation, and a penicillated arrangement of primary, secondary, and tertiary branches. The stipes were septate, 110 to 175 (138) μm long, with a terminal obpyriform vesicle measuring 3.75 to 7.5 (5.8) μm wide. Phialides (12.5 × 3.6 μm) were hyaline, doliiform to reniform, with conidia 40 to 55 × 3.7 to 5 μm, cylindrical with rounded ends, aseptate or one septate. Chlamydospores were brown and formed microsclerotia. These features conformed to the description of Cylindrocladium pauciramosum (3). Further confirmation was obtained by sequence analysis. The 5' end of the β-tubulin gene was amplified using primers T1 and βt2b (2). Comparison with other sequences in GenBank revealed that the isolates described here were identical with C. pauciramosum (Accession No. AY880064) isolated from Ceanothus in the UK. To confirm pathogenicity, 1-year-old plants of callistemon were inoculated with two isolates by spraying with a spore suspension of the fungus (1 × 10 conidia per ml) obtained from 14-day-old single spore colonies on CLA. Control plants were treated with sterile distilled water. After inoculation, all plants were maintained in plastic bags and kept at 22 ± 2°C. Four days after inoculation, the plants developed symptoms similar to those observed in natural infections, and C. pauciramosum was reisolated, successfully completing Koch's postulates. No symptoms were observed on the control plants. C. pauciramosum has been recorded on several hosts, including Callistemon citrinus, in Italy (4). To our knowledge, this is the first report of C. pauciramosum on callistemon in Spain. References: (1) P. W. Crous and M. J. Wingfield. Mycotaxon 51:341, 1994. (2) B. Henricot and A. Culham. Mycologia 94:980, 2002. (3) C. L. Schoch et al. Mycologia 91:286, 1999. (4) C. L. Schoch et al. Plant Dis. 85:941, 2001.
红千层（红千层（Curtis）Skeels）是桃金娘科的常绿植物，因其红色瓶刷状花朵而常用于地中海花园。2006年11月，西班牙巴伦西亚的商业苗圃中，1岁的红千层盆栽出现了叶斑和枯萎症状。症状最初表现为叶片上的微小褐色斑点，随后发展为黑灰色斑块，最终融合在一起。患病植株还出现了茎部病变和嫩枝枯萎。约30%的植株受到影响。从受感染组织中始终分离出一种柱枝双孢菌属真菌。将六个单孢分离株在康乃馨叶琼脂（CLA）上于25°C近紫外光下培养7天（1）。大型分生孢子梗由柄、不育的延伸部分以及一级、二级和三级分支的帚状排列组成。柄有隔膜，长110至175（138）μm，顶端有一个倒梨形泡囊，宽3.75至7.5（5.8）μm。瓶梗（12.5×3.6μm）透明，桶形至肾形，分生孢子40至55×3.7至5μm，圆柱形，两端圆形，无隔膜或有一个隔膜。厚垣孢子呈褐色，形成小菌核。这些特征与少枝柱枝双孢菌（3）的描述相符。通过序列分析获得了进一步的证实。使用引物T1和βt2b扩增β-微管蛋白基因的5'端（2）。与GenBank中的其他序列比较表明，这里描述的分离株与从英国鼠李属植物中分离出的少枝柱枝双孢菌（登录号AY880064）相同。为了确认致病性，用从CLA上14天龄的单孢菌落获得的真菌孢子悬浮液（每毫升1×10个分生孢子）喷洒接种1岁的红千层植株。对照植株用无菌蒸馏水处理。接种后，所有植株都放在塑料袋中，保持在22±2°C。接种四天后，植株出现了与自然感染中观察到的症状相似的症状，并且再次分离出少枝柱枝双孢菌，成功完成了柯赫氏法则。对照植株未观察到症状。在意大利，少枝柱枝双孢菌已在包括红千层在内的几种寄主上被记录（4）。据我们所知，这是西班牙首次报道少枝柱枝双孢菌侵染红千层。参考文献：（1）P. W. Crous和M. J. Wingfield。《真菌分类学》51:341，1994。（2）B. Henricot和A. Culham。《真菌学》94:980，2002。（3）C. L. Schoch等人。《真菌学》91:286，1999。（4）C. L. Schoch等人。《植物病害》85:941，2001。
