| 520 |
|
|
|a Ctenanthe oppenheimiana (E. Morren) K. Schum. (Maranta oppenheimiana) is a shade-loving, monocotyledonous ornamental plant belonging to the family Marantaceae. The plant has attractive foliage and is used for decoration in a park and around offices building. Six million seedings were produced in China in 2017 (China Flower Association, 2018). Plants were seriously infected with a year-round foliar disease. The disease occurred in all planting areas and approximately 53.1% and 48.3% of the plants in Guangdong and Fujian provinces in China, March 2017, were infected and caused economic loss to control plant diseases with chemicals. The initial symptoms were observed after 1 month of planting and included small brown lesions that expanded to form large irregular yellow lesions at the tips or margins of the leaves in campus of Guangdong Ocean University. Diseased plants were collected in Zhanjiang city (110°30' E, 21°20' N), Gaozhou city Guangdong province and (117.42E, 25.3N) and Zhangping city Fujian province (117°42' E, 25°30' N). Seven single-spore cultures were recovered from symptomatic samples after they were disinfested with 1% NaOCl, and plated on potato sucrose agar (PSA) at 28 °C for one week. Three isolates were used for pathogenicity test, 200 μL conidial suspension (106 conidia ml-1) was dropped on the leaf sites with sterile needle-prick wound at 5-8 leaf stage. There were three replicates for each treatment and the experiment was repeated three times. Plants were placed in incubator at 25 ℃, with 80% humidity and a 12-h light/dark cycle. Control seedlings were treated identically except sterile water was placed on the wounds. Round brown necrotic lesions in the middle of the leaves grew in the inoculated wounded leaves 5 days after inoculation and brown necrotic lesions developed into large brown lesions of 2.2-3.6 cm 10 days after inoculation whilethere were no symptoms in the negative controls. Colletotrichum was re-isolated from the lesions in inoculated leaves fulfilling Koch's postulates. Colonies on PSA were grayish white with a regular border and a felty aerial mycelium that contained masses of orange conidia. No setae were observed in the PSA culture. Conidia were straight and hyaline with rounded ends measuring 10.0-15.0×5.0-6.0 μm (average =14.2×5.3 μm, n=50). Conidiophores hyaline, septate. Conidiogenous cells were hyaline, cylindric, and 13.2-22.5×4.5-5.5 µm (average =19.5×4.6 μm, n=50). Appressoria were cylindrical, 5.2-10.5 × 4.0-6.8 μm (average =7.5×5.2 μm, n=50). For molecular identification, the colony PCR method with MightyAmp DNA Polymerase (Takara-Bio, Dalian, China) (Lu et al. 2012) was used to amplify the ITS of ribosomal DNA, glutamine synthetase (GS), calmodulin(CAL) and Apmat loci of three isolates using primer pairs of ITS4/ITS5, GSF1/GSR1, CL1C/CL2C and AM-F/AM-R (Liu et al. 2015). Phylogenetic tree derived from a neighbor-joining analysis of a concatenated alignment of ITS, GS, CAL and ApMAT sequences. The accession numbers of three isolates ZJCG, GZCG and FJCG used in this study were KP635210, MN133235, MN133236 for ITS, MT594433, MT594434, MT594435 for CAL, MT594436, MT594437, MT594438 for GS and MN133228, MN133229, MN133230 for ApMAT. The sequences of the three isolates were aligned with those of the related species in C. gloeosporioides complex (Liu et al. 2015). Analyses based on concatenated data sets of four genes showed that the sequences had high levels of identity to those of the C. siamense strains. According to both morphological and sequence analyses, the C. oppenheimiana pathogen was identified as C. siamense. There are two reports of foliar pathogens on C. oppenheimiana, Rhizoctonia solani and Pyricularia oryzae (Baiswar et al. 2010, Pappas and Vloutoglou, 1996). To our knowledge, this is the first report of anthracnose on C. oppenheimiana caused by C. siamense in China. Identification of the pathogen of this disease is essential for the development of effective and economical management practices
|