Neopestalotiopsis rosae causing leaf spot on Rosa sp. in Brazil

The rose (Rosa spp.) crop, of great economic and ornamental importance, is frequently affected by foliar diseases that reduce aesthetic quality and compromise production. Among these, necrotic leaf spots have become prominent, making it necessary to characterize the associated agents to support management strategies. Symptomatic leaves were collected in São Vicente do Sul, RS, Brazil, and incubated in a moist chamber for ten days to isolate the pathogen. Ten isolates were obtained and evaluated for pathogenicity on healthy seedlings. Three isolates (P1, P2, and P3) were selected for morphophysiological characterization, including mycelial growth on PDA medium and PDA supplemented with rose leaves, with colony diameter measurements using a millimeter ruler, and the evaluation of 30 conidia per isolate under a microscope. For molecular identification, one isolate was randomly selected and subjected to amplification of the ITS, TEF1-α, and β-tubulin regions, used for consensus phylogenetic tree construction. All isolates proved pathogenic, reproducing symptoms in inoculated seedlings. Isolates P1, P2, and P3 showed more vigorous mycelial growth on supplemented medium from the second day onward, with massively higher sporulation (up to 2.19 × 10⁶ conidia/ml), compared with pure PDA (max. 6.8 × 10⁵ conidia/ml). Conidia produced were also larger in the supplemented medium. Phylogenetic analysis confirmed the pathogen as Neopestalotiopsis rosae, with 92% bootstrap support. This is the first report of N. rosae as the causal agent of leaf spot on roses in Brazil.