Occurrence of Alternaria alternata causing leaf spot on tamarillo in Brazil

Abstract

Tamarillo plants (Solanum betaceum Cav.) had leaf spot symptoms in an urban vegetable garden in Curitiba, Paraná, Brazil. After observation of structures under optical light microscopy, the morphology indicated that it was a fungus of the genus Alternaria. The objective of the present study was to identify the Alternaria species that causes leaf spot on tamarillo in Brazil through molecular and morphological characterization, in addition to pathogenicity testing. The molecular characterization was based on the phylogenetic analysis of the concatenated TEF, GAPDH, and RPB2 genes, using the maximum likelihood method and bayesian inference. Microculture slides were used for morphological assessments, measuring 50 conidiophores and 50 conidia, randomly chosen. The pathogenicity test was performed by inoculating five plants with a suspension containing 105 spores mL−1. After inoculation, the plants were covered with plastic and cultivated in a growth chamber for daily assessment of symptoms and signs of the pathogen. Molecular characterization demonstrated the identity of nucleotides of the three genes of the isolate LEMIDSbAaPR20-01 with sequences from the Alternaria section, and phylogenetic analysis confirmed the species to be A. alternata. The morphological characteristics are in accordance with those described in the literature for A. alternata. Symptoms were observed from five days after inoculation and non-inoculated plants remained asymptomatic. This is the first report of A. alternata in S. betaceum in Brazil and in the world.