First report of anthracnose caused by Colletotrichum spaethianum on Allium fistulosum in Brazil

Abstract

The Welch onion (Allium fistulosum L.) is widely grown in temperate and subtropical regions worldwide and has many important culinary uses. The occurrence of anthracnose on Welch onion has been reported in Korea and is caused by Colletotrichum circinans (Kim et al. 2008). Since 2012, symptoms typical of anthracnose have been observed on Welch onions in a vegetable garden located in the Japanese Colony of Manaus, Amazonas, Brazil (59°59′06″ W; 03°04′16″ S). This disease occurred in 50% of the seedlings and the symptoms consist of brown necrotic spots that extend along the entire leaf. Acervuli collected directly from the leaves were plated onto potato dextrose agar (PDA) and then incubated at 25°C for three to four days. Single-spore cultures were obtained from three isolates from different plants. On PDA medium, the isolates initially produced white colonies, which then turned gray and had an orange-colored conidial mass. On Spezieller Nährstoffarmer Agar (SNA) medium (Leslie and Summerell, 2006), they formed numerous black structures such as sclerotia, setae, and acervuli. Conidia on SNA are hyaline, aseptate, curved or slightly curved, with a rounded apex and truncated base that is 13.1 to 20.2 μm long and 3.3 to 4.0 μm wide. The appressoria are solitary or in loose groups, dark brown, irregularly shaped, sometimes partially lobed, smooth-walled, and from 5.6 to 10.8 μm long and 4.3 to 8.2 μm wide. An alignment of the actin (ACT) and chitin synthase (CHS-1) partial gene sequences showed 100% identity with Colletotrichum spaethianum (Allesch.) Damm, P. F. Cannon & Crous (CBS 167.49). Maximum likelihood analysis was done using the published sequences of the ACT and CHS-1 genes from C. spaethianum and other Colletotrichum species that have curved conidia (Damm et al. 2009; Vieira et al. 2014). The individual data sets were combined using the web tool FaBox (1.41) and analysis with PAUP (1000 bootstrap replicates). Based on morphological characteristics and phylogenetic analysis, the isolates were identified as C. spaethianum. The sequences for the isolates obtained in the present study were deposited in GenBank (ACT Accession Nos. KT184300 to KT184302; CHS-1 Accession Nos. KT184303 to KT184305). The cultures were deposited in the Culture Collection of Microorganisms of the National Institute of the Amazonian Research (Instituto Nacional de Pesquisas da Amazônia, INPA) (INPA 2615, 2770, and 2774). Five Welch onion seedlings were sprayed with a conidial suspension (106 conidia/ml) for each isolate and control seedlings were sprayed with sterile water. Plants were covered with plastic bags and maintained at 28°C ± 2°C in a greenhouse and a 12-h photoperiod. Symptoms typical of anthracnose were induced five days postinoculation, and signs of the pathogen were observed at 12 days postinoculation. No symptoms were observed in the control plants. C. spaethianum was reisolated from symptomatic plants, completing Koch’s postulates. C. spaethianum has been described on Hosta sieboldiana in Germany, Lilium sp. in South Korea, Hemerocallis sp. in New Zealand (Damm et al. 2012), Hemerocallis fulva, Hemerocallis citrine, and Peucedanum praeruptorum in China (Yang et al. 2012; Guo et al. 2013), and Hemerocallis flava in Brazil (Vieira et al. 2014). To our knowledge, this is the first report of C. spaethianum on A. fistulosum. © 2016, American Phytopathological Society. All rights reserved.