Caracterização molecular, morfológica e biológica do agente etiológico da pinta-preta em solanáceas no Brasil

Abstract

Early blight caused by species from Alternaria genus affects several solanaceous of economic importance. Previous studies have shown that the species A. tomatophila and A. grandis prevail as causal agents of disease on tomato and potato, respectively. The control of this disease is based on the use of protective and systemic fungicides. However, there are reports of the existence of other species of Alternaria causing early blight in plants of the Solanácea family. This study aimed to perform molecular, morphological and biological characterization of Alternaria isolates from cultivated and wild solanaceous from different regions of Brazil. Molecular characterization of the isolates was done by sequencing and phylogenetic analysis of the genes Alt a1, GPD and Calmodulin. Morphological characterization was performed by measurement of dimensions of the conidia and quantification of the number of septa and rostrums. Biological characterization of Alternaria isolates was done by evaluation of host range and by the in vitro sensitivity to tebuconazole. Phylogenetic analysis of the genes Alt a1, GPD and Calmodulin allowed the identification of the species A. tomatophila, A. mimicula and A. dauci from tomato, and the species A. grandis and A. solani from potato and from lobeira, respectively. Morphologic caracteristics of most isolates corroborate the molecular characterization. The isolate EH1642-BA, identified as A. solani, was able to cause early blight on all solanaceous hosts evaluated except the sweet pepper. EH1823-CE of the specie A. tomatophila and EH1548-DF of A. grandis isolates from tomato and potato, respectively, had not specificity for their original host plants. However, the isolates EH1143-RS of the specie A.dauci and EH1377-CE of A. mimicula showed specificity for original host causing typical symptoms of early blight only on tomato. Alternaria isolates from tomato and eggplant caused disease on wild invasive solanaceous Datura stramonium and Physalis pubescens and isolates from D. stramonium and Nicandra physaloides caused symptoms of early blight on tomato, potato and jiló. In the sensitivity tests to the fungicide tebuconazole in general the isolates showed high sensitivity under in vitro conditions. The results obtained in this study confirmed the occurrence of A. tomatophila and A. grandis as causal agents of early blight on tomato and potato, respectively, and in this work were detected for the first time in Brazil the presence of A. dauci and A. mimicula associated with the disease on tomato. It has been found that some wild solanaceous can act as pathogen inoculum sources and the tebuconazole was efficient in the in vitro control for the isolates evaluated.