First Report of Anthracnose on Michelia champaca Caused by Colletotrichum fioriniae in China.

Abstract

Michelia champaca Linn., commonly named as yellow jade orchid tree, is best known for its strongly fragrant yellow or white flowers. It is primarily cultivated for its timber and also used in urban landscaping in China. Moreover, the flower buds are commonly used by many traditional healers in most of the herbal preparations for diabetes and kidney diseases (Jarald et al. 2008). In September 2017, necrotic spots were observed on young and mature leaves of M. champaca in Chongzhou County (30.63° N, 103.67° E), Sichuan Province, China. The symptoms initially appeared as small necrotic spots, circular to semicircular in shape, water soaked, later becoming grayish white in the center with a dark brown margin bordered by a tan halo. As the disease progressed, these spots coalesced and caused premature senescence and falling of the leaves, reducing their ornamental value. To identify the causal agent of leaf spots, small segments of symptomatic tissues were surface sterilized by washing them in 75% ethanol for 30 s and rinsing three times in sterile water. Tissues were placed on potato dextrose agar (PDA) at 25°C. A fungus was consistently isolated from symptomatic tissues on PDA. This fungus produced pale gray, dense aerial hyphae and black structures similar to sclerotia on PDA plates. The salmon-colored conidial mass was observed on well-developed colonies after 20 days. Acervuli were dark brown to black, 180 to 455 μm in diameter. Conidia were hyaline, aseptate, oblong, and 14.5 to 19.5 × 4.0 to 6.5 μm (n = 100). These morphological and cultural characteristics were consistent with the description of Colletotrichum spp. Isolate MC-2 was selected as a representative for molecular identification. The internal transcribed spacer (ITS) region of rDNA, partial actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), chitin synthase 1 (CHS-1), β-tubulin 2 (TUB2), and calmodulin (CAL) genes (Damm et al. 2012) were amplified and sequenced. Sequences were deposited in GenBank (MG657347 for ITS, MG657348 for ACT, MG657349 for GAPDH, MG657350 for CHS-1, MG657351 for TUB2, and MG657352 for CAL). BLAST analysis showed >99% identity with several reference sequences of C. fioriniae (Glomerella fioriniae) previously deposited in GenBank. Accordingly, the fungus isolated from anthracnose symptoms on M. champaca was identified as C. fioriniae. Three single-spore isolates were used for pathogenicity analyses. Twelve leaves of M. champaca were inoculated with a conidial suspension (5 × 10⁶ conidia/ml), with distilled water as a control. Small circular spots similar to those observed on naturally infected plants in the field were observed in all of the inoculated leaves within 8 days after inoculation. No symptoms were observed on the control. The inoculated fungus was reisolated from lesions on inoculated plant tissues and showed the same morphological and cultural properties as the original isolates. No C. fioriniae was isolated from control leaves, thus fulfilling Koch’s postulates. The results of the three repeated experiments were identical. To our knowledge, this is the first report of C. fioriniae causing anthracnose on M. champaca in China. This study provides useful information for the control of this disease in the future.