Occurrence of Alternaria arborescens causing leaf spot on Pereskia aculeata in Brazil

Abstract

Pereskia aculeata, commonly known as ora-pro-nobis, is a is a highly nutritive species used for human consumption with potential of expansion. However, leaf lesions that did not match the symptoms and signs of previously described pathogenic species to this culture were observed in an ora-pro-nobis cultivation in Curitiba, Paraná state, southern Brazil. Therefore, the objectives of this study were to isolate, test the pathogenicity and characterize morphologically and molecularly the causal agent of the symptoms of this species. For this purpose, isolation from leaf fragments was performed. Pathogenicity was tested in potted cuttings which were wounded to simulate the thorns natural injuries and inoculated with a conidia suspension. The colony characteristics and morphological features of conidia were determined on V8 medium, and the molecular characterization was performed with Bayesian phylogenetic inference of the partial concatenated alignment of the ITS, gapdh and tef1 genes of the isolate. Morphological characterization matched the described for Alternaria spp. The symptoms on inoculated cuttings appeared within 4 days in all inoculated leaves, while the control plants remained asymptomatic, and 10 days after inoculation all symptomatic leaves fell from the plant. The characteristics of the re-isolated fungus from the pathogenicity test lesions were morphologically similar to the isolate from naturally infected leaves. The sequences of the pathogen grouped in a reliable clade called Alternaria arborescens. To our knowledge, this is the first report of A.arborescens causing lesions on P.aculeata worldwide. Implications of these finding should be further studied.