First Report of a Leaf Spot Caused by Paramyrothecium roridum on Tectona grandis in Brazil

Tectona grandis Lf (teak) is a deciduous forest species with increasing economic importance in timber production in subequatorial Brazil. In August 2016, circular dark brown leaf spots (ranging 1 to 20 mm in diameter) with well-defined edges were found mainly in seedlings of commercial production areas in Caceres, Mato Grosso State, Brazil. The lesions often induced defoliation, as well as slower plant growth and development. For isolation of the causal agent, foliar lesions were submitted to a series of disinfection steps (70% alcohol for 1 min and 2% sodium hypochlorite for 1 min, followed by a double rinse in distilled water for 1 min). The tissues were then transferred to Petri dishes with potato dextrose agar (Merck) medium and incubated at 25°C for 5 days in the dark. Young fungal colonies displayed white mycelium with concentric rings varying from dark green to blackish shades with the production of black sporodochia. Microscopic observations indicated the presence of hyaline conidiophores with rod-shaped phialides (10 to 17 × 1.5 to 3.0 μm). Conidia were hyaline, cylindrical (6 to 8 × 2.0 to 2.5 μm) with rounded ends. The isolates were identified as Paramyrothecium roridum (Tode) L. Lombard & Crous comb. nov. (Lombard et al. 2016) (syn. Myrothecium roridum Tode). Genomic DNA was extracted from colonies of two representative monosporic isolates using a cetyl trimethylammonium bromide method. Polymerase chain reaction assays were carried out with the primer pair ITS1 and ITS4 able to amplify a segment of the rDNA-ITS region (White et al. 1990), which is the largest database available for the genus Paramyrothecium. The isolates from teak were deposited in “Maria Menezes” (UFRPE, Recife–PE, Brazil) public fungal collection under the numbers CMM4729 and CMM4730. Alignments of the two teak isolates (accession nos. MF579530 and MF579531) displayed 100% identity with each other and 99% identity with the reference P. roridum isolate CBS 372.50 (KU846301) reported on Coffea plants (Lombard et al. 2016). Healthy plants of three elite clones (six seedlings of each) were inoculated by spraying a suspension of 1 × 10⁶ conidia/ml using leaves either after softly wounded (by toothbrush) or employing intact tissues. The mock-inoculated controls (wounded and nonwounded plants) were sprayed with sterile water. The seedlings were kept on a moist chamber (25°C) for 2 days. Seedlings inoculated with P. roridum displayed initial leaf symptoms 7 days after inoculation, whereas the controls remained free of symptoms. P. roridum was reisolated only from the symptomatic plants. This pathogen has been previously reported infecting teak in Taiwan (Doilom et al. 2016). In Brazil, P. roridum was reported on a wide range of mainly herbaceous hosts (Fujinawa et al. 2016; Mendes et al. 1998). However, this is the first report of this fungus on teak in the country. The occurrence of this wide host range pathogen will demand the deployment of novel preemptive diagnostic and control strategies to avoid potential yield losses in teak under Brazilian conditions.