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First Report of Fusarium fujikuroi Causing Stem Wilt on Canna edulis Ker in China

Jiang, S. B., Lin, B. R., Shen, H. F., Yang, Q. Y., Zhang, J. X., Sun, D. Y., Pu, X. M.
Plant disease 2018 v.102 no.6 pp. 1177
Canna indica, Fusarium fujikuroi, Hylocereus polyrhizus, calmodulin, conidia, culture media, disease control, ethanol, fungi, genes, greenhouses, growth retardation, histones, leaves, microscopy, mitochondria, mycelium, pathogenicity, pathogens, phylogeny, polymerase chain reaction, relative humidity, sodium hypochlorite, stem rot, stems, tissues, tubulin, China, Malaysia
Canna lily (Canna edulis Ker.) is an important economic crop in China with a production area of more than 40,000 ha. In June 2017, C. edlis ‘Xingyu-1’ in Wuhua, Guangdong, China, developed stunting, chlorotic stems with spots, and wilted leaves and ultimately died. White mycelium appeared on the stems during wet conditions. Affected plants were scattered throughout the field, with an overall incidence of about 15%. Diseased stem tissues (5 × 5 mm) were surface sterilized using 75% ethanol for 30 s and 2% NaOCl for 10 min, rinsed three times with sterile water, and incubated for 4 days on potato dextrose agar (PDA) medium at 25°C. Fungal colonies were subcultured onto fresh PDA and grown for 7 days. The mycelium became white and fluffy, and the reverse of the culture plate turned pale pink after 5 days. Two isolates, BJY1 and BJY2, were deposited at Guangdong Microbial Culture Collection Center (nos. 3.633 and 3.634). Morphological characteristics of both microconidia and macroconidia were consistent with those of Fusarium spp. (Booth 1971). Polymerase chain reaction (PCR) was used to amplify the TEF-1α gene (GenBank accession nos. MF996497 and MF996498) and the RPB2 gene (MF984421 and MF98442) (Masratul Hawa et al. 2017). Based on the phylogenetic tree (neighbor-joining method and 1,000 bootstrap values) using multiplex alignments of concatenations of these two genes from 20 Fusarium species within the Fusarium fujikuroi species complex (Masratul Hawa et al. 2017), BJY1 and BJY2 were grouped into one clade with F. fujikuroi strain NRRL 13566. To further confirm the identities of the isolates, five additional gene sequences—rDNA-ITS (MF984413 MF984414), β-tubulin (MF984415 and MF984416), histone 3 (MF984417 and MF984418), calmodulin (MF984411 and MF984412), and mitochondrial small subunit (MF984419 and MF984420) (Pedrozo et al. 2015)—were subjected to BLAST in GenBank and Fusarium ID. The results indicated that BJY1 and BJY2 were most similar to F. fujikuroi, with sequence identities greater than 99%. Pathogenicity was tested by injecting 10 μl of a spore suspension (7 × 10⁶ spores/ml) into stems of 10 disease-free C. edulis ‘Xingyu-1’. For noninoculated controls, another 10 plants were injected with 10 μl of sterile water. Plants were placed in a greenhouse at 25 to 28°C and 90% relative humidity with ambient light in July 2017. Symptoms of stem wilt similar to those in the field were observed from all inoculated plants within 14 days, whereas no symptoms were observed on the controls. We reisolated the fungal pathogen from the symptomatic tissues and further confirmed it to be F. fujikuroi by microscopy and PCR. F. fujikuroi was previously reported associated with stem rot of Hylocereus polyrhizus in Malaysia (Masratul Hawa et al. 2017). To our knowledge, this is the first report of F. fujikuroi causing wilt on C. edulis Ker. in China and elsewhere. Identification of the causal organism is the first step in disease management.