First report of Curvularia chiangmaiensis causing leaf spot in elephant grass in Brazil.

Abstract

Elephant grass, Cenchrus purpureus, exhibits high efficiency in sequesting atmospheric CO2 during photosynthesis, leading to significant biomass production. As a C4 plant, it holds immense potential for alternative biodiesel production and serves as fresh feed for cattle (Negawo et al. 2018). Field observations in commercial pastures planted with elephant grass, located in the Brazilian cerrado, revealed necrotic leaf spots with a brownish center and a yellowish halo, reaching a severity of 30 to 50% between 2022 and 2023 in Palmas (10°24'08"S 48°21'45" W) and Gurupi (11°46'21"S 49°02'08" W), municipalities located in the state of Tocantins, Brazil. In both years, the field incidence of the disease on young and mature leaves approached 100% during the rainy season. Affected leaves were collected, packed in a thermal box, and taken to the phytopathology laboratory. The 198 leaves were sanitised in 1% hypochlorite for 30 seconds and washed thrice in sterile water. Upon sanitisation, leaf tissues were cut and cultured on potato dextrose agar (PDA) medium and incubated in a controlled chamber (BOD) at 28°C with a 12-hour photoperiod. Colonies exhibited a greyish colour with whitish edges, and the top plate was brownish, growing to a diameter of 5 cm over seven days. The colonies obtained from monosporic cultures formed curved conidia, predominantly with three septa, of a brownish colour, with lengths ranging from (7 µm to 14 µm and widths from 5 µm to 7 µm. (N=-50, Fig 1) (Yasanthika et al. 2023). The UFTCC01 isolate's DNA was extracted using the extraction kit (PROMEGA ®), amplified for genes (ITS, Gapdh and Tefα1), sequenced (OR345316.1, OR344427.1 and OR344428.1) and compared in BLASTn at Gen Bank deposited sequences. Phylogenetic analysis using the parsimony method in MEGA X identified the isolate as Curvularia chiangmaiensis, showing 99.5% identity with reference sequences (MN215651.1, MN264085.1, and MN263942.1). Concatenated region comparison revealed 94% similarity to sequences (OP564987.1 and MF490814.1) in the phylogenetic tree, confirming the species. The pathogenicity test used 60 seedlings of 50-day-old elephant grass, 30 of which were inoculated with a spore suspension (3.0 × 106 spores/mL) and 30 with sterile water. The solutions were sprayed twice. Only plants inoculated with the spore suspension exhibited symptoms akin to those observed in the field. Then, the fungus was reisolated from the lesions and Koch's postulates were confirmed twice.Previous studies have documented the C. chiangmaiensis pathogenicity in other grasses, such as maise in Thailand (Marin et al. 2017). Our studies constitute the first report of C. chiangmaiensis causing leaf spots on elephant grass in the Brazil.