Gladiolus (Iridaceae) is a popular bulbous plant grown worldwide as an ornamental garden plant or cut flower due to its attractive color, size, and flower shape. In April 2012, leaf spots were observed on plants of Gladiolus grandiflorus varieties T-704 and Amsterdam growing in a production area of cut flowers located in the city of Viçosa, Minas Gerais. The oval to round leaf spots were brown with a dark border surrounded by a halo of yellow tissue. Infected leaf samples were deposited in the herbarium at the Universidade Federal de Viçosa (VIC31897). A fungus was isolated from the leaf spots and a single-spore pure culture was initiated and grown on corn meal carrot agar (CCA) medium in petri dishes incubated at 25°C under a 12-h photoperiod for 4 weeks. A sporulating single-spore culture was deposited at the Coleção de Culturas de fungos fitopatogênicos “Prof. Maria Menezes” (UFRPE, Brazil) code CMM 4055. On CCA medium, the fungal isolate initially appeared white, becoming dark after 14 days. Thirty conidia and conidiophores were measured for identification to species. The septate, smooth to pale brown conidiophores were present singly or in groups. The simple, straight or flexuous conidiophores were 42.5 to 82.5 × 3.5 to 7.5 μm and some had a geniculate growth pattern. The majority of conidia were curved at the third (central) cell from the base, which was usually enlarged compared to the end cells. The cells at each end of the 3-distoseptate conidia were pale brown, the intermediate cell brown or dark brown, and the third (central) cell was often the darkest. The basal cell had a protuberant hilum. Conidia were smooth and 20.0 to 33.5 × 10 to 17.5 μm. These characteristics matched well with the description of Curvularia gladioli (1). To confirm this identification, DNA was extracted using a Wizard Genomic DNA Purification Kit and the internal transcribed spacer region (ITS) of rDNA was amplified using ITS1 and ITS4 primers and the partial 28S rDNA region using primers LR0R and LR5. The sequences were deposited in GenBank as accession nos. JX995106 and JX995107, respectively. The ITS sequence matched sequence AF071337, C. gladioli, with 100% identity. This pathogen was first identified as C. lunata, but based on the characteristic of the hilum, spore size, and pathogenicity testing, the fungus was renamed C. trifolii f. sp. gladioli (3). Due to the explicit curvature of the conidia at the third cell and molecular data, the fungus was reclassified as C. gladioli (1,2). To confirm Koch's postulates, 1-month-old healthy plants of G. grandiflorus var. T-704 and Amsterdam (five plants each) were inoculated with a conidial suspension (2 × 104 conidia mL–1) by spraying the foliage and then placed on a growth chamber at 25°C. The control plants were sprayed with distilled water. Symptoms were consistent with those initially observed and all plants developed leaf spots by 4 days post-inoculation. C. gladioli was consistently recovered from the symptomatic tissue and control plants remained symptomless. To our knowledge, this is the first report of C. gladioli causing leaf spot on G. grandiflorus in Brazil. Due to a lack of chemical fungicides for management of this pathogen, further studies to evaluate the susceptibility of the main varieties of gladiolus grown in Brazil to C. gladioli may be necessary.
References: (1) G. H. Boerema and M. E. C. Hamers. Neth. J. Plant Pathol. 95:1, 1989. (2) D. S. Manamgoda et al. Fungal Divers. 56:131, 2012. (3) J. A. Parmelee. Mycologia 48:558, 1956.