Picos-Munoz P A, Garcia-Estrada R S, Carrillo-Fasio J A, Leon-Felix J, Allende-Molar R
Research Center for Food and Development. Km 5.5 Carr, Culiacan-Eldorado, 80110, Sinaloa, Mexico.
Plant Dis. 2011 Sep;95(9):1195. doi: 10.1094/PDIS-09-10-0618.
Tomato is the primary vegetable exported from Mexico to the United States. In June 2007, stem rots were observed in tomato cv. Imperial plants growing in a greenhouse in the Culiacan Valley. Disease symptoms included stem rot with a mycelial growth with a grayish blue sporulation. The disease was observed to be affecting 1% of the tomato plants growing in the greenhouse, and has been observed sporadically in greenhouses during subsequent agricultural cycles in other tomato-growing areas in Mexico. Affected stems showed initial symptoms of a dark brown necrotic area surrounding only the cut regions of pruned leaves and stems. As the infection continued on the tissues, the spot grew and then became covered with a grayish blue sporulation. Severe stem rot led to death of the plants. Rotted stems of tomato plants were collected and samples of the infected tissues were plated onto potato dextrose agar (PDA) to isolate the fungus. The preliminary identification of the pathogen was Penicillium oxalicum Currie & Thom on the basis of morphological criteria with ellipsoidal conidia approximately 4 × 3 μm borne in columns, conidiophores mostly biverticillate, and ampulliform phialides (2). The identification was confirmed by sequencing internal transcribed spacer 1 (ITS1), 5.8S, and ITS2 regions of the ribosomal DNA (GenBank Accession No. HM452308). The isolate was deposited in the Coleccion Nacional Microbiana y de Cultivos Celulares CINVESTAV-IPN, Mexico. Koch's postulates were fulfilled by reproducing stem rots on healthy inoculated tomato stems. Pathogenicity testing involved fungal growth on PDA for 5 days, after which a 4-mm disk of actively growing mycelia was transferred to wounds (4 × 4 mm) made with a scalpel in stems of 6-week-old tomato cv. Imperial plants. Inoculated plants were covered with plastic bags to maintain a high relative humidity for 24 h and were maintained in a greenhouse at 25 ± 2°C. Seven days after inoculation, all of the inoculated stems showed rot symptoms similar to those observed in the greenhouse. Stems that were inoculated only with an agar disk did not show any symptoms of the disease. The pathogen was reisolated from inoculated plants but not from noninoculated plants. Artificial inoculation was performed twice. Although P. oxalicum has been previously reported as a causal agent of cucumber (1) and tomato stem rots in Japan (3), to our knowledge, this is the first report of P. oxalicum causing stem rot in tomato plants in Mexico. References: (1) T. M. O'Neill et al. Plant Pathol. 40:78, 1991. (2) J. I. Pitt. The Genus Penicillium and Its Teleomorphic States Eupenicillium and Talaromyces. Academic Press, London, UK, 1979. (3) S. Umemoto et al. J. Gen. Plant Pathol. 75:399, 2009.
番茄是墨西哥出口到美国的主要蔬菜。2007年6月，在库利亚坎山谷一个温室里种植的番茄品种“帝王”植株上观察到茎腐病。病害症状包括茎腐，伴有呈灰蓝色产孢的菌丝生长。据观察，该病影响了温室中1%的番茄植株，在墨西哥其他番茄种植区随后的农业周期中，也偶尔在温室中观察到这种病害。受影响的茎最初表现为仅围绕修剪叶片和茎的切口区域出现深褐色坏死区。随着感染在组织上继续发展，病斑扩大，随后被灰蓝色产孢覆盖。严重的茎腐病导致植株死亡。收集番茄植株的腐烂茎，将感染组织的样本接种到马铃薯葡萄糖琼脂（PDA）上以分离真菌。根据形态学标准，初步鉴定病原菌为草酸青霉，其椭圆形分生孢子大小约为4×3μm，呈柱状排列，分生孢子梗大多为双轮生，瓶梗呈壶形（2）。通过对核糖体DNA的内部转录间隔区1（ITS1）、5.8S和ITS2区域进行测序（GenBank登录号：HM452308），确认了鉴定结果。该分离株保藏于墨西哥国立理工学院国家微生物和细胞培养物保藏中心。通过在健康接种的番茄茎上再现茎腐病，科赫法则得到了验证。致病性测试包括真菌在PDA上生长5天，之后将一个4mm的活跃生长菌丝圆盘转移到6周龄番茄品种“帝王”植株茎上用手术刀造成的伤口（4×4mm）处。对接种的植株用塑料袋覆盖以保持24小时的高相对湿度，并在25±2°C的温室中培养。接种7天后，所有接种的茎都出现了与温室中观察到的类似的腐烂症状。仅接种琼脂圆盘的茎没有表现出该病的任何症状。从接种的植株上重新分离到了病原菌，但未从未接种的植株上分离到。人工接种进行了两次。虽然草酸青霉此前曾被报道为黄瓜（1）和日本番茄茎腐病的病原菌（3），但据我们所知，这是草酸青霉在墨西哥番茄植株上引起茎腐病的首次报道。参考文献：（1）T.M.奥尼尔等人，《植物病理学》40:78，1991年。（2）J.I.皮特，《青霉属及其有性态真青霉和拟青霉》，英国伦敦学术出版社，1979年。（3）S.梅本等人，《植物病理学报》75:399，2009年。
