Caracterização de Colletotrichum spp. associados à antracnose em flores tropicais no nordeste do BRASIL e uso de óleos essenciais no controle da antracnose (Colletotrichum tropicale) em bastão do imperador

Abstract

The objectives of this study were to identify species of the genus Colletotrichum, through molecular and morphocultural characterization associated with different species of tropical flowers, to evaluate the cross-pathogenicity of these identified Colletotrichum species and to test different essential oils in the control of the disease. For molecular characterization, the genomic DNA of the isolates were analyzed by the CTAB 2% protocol with modifications. The partial sequence of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene was amplified using the GDF/GDR primers, for a preliminary identification of the isolates and evaluation of the haplotypic diversity of the species. Subsequently, representatives of each species, based on haplotypes, were amplified with another gene, β-tubulin (TUB2), Chitin synthase (CHS-1), Mating type locus MAT1-2-1 (APN2/MAT-IGS) and the region ITS-rDNA. and the ITS-rDNA region. The cultural characterization consisted of obtaining the mycelial growth of the colonies, through daily measurement in two diametrically opposite directions and observation of the color of the colonies evaluated after seven days. Morphological characterization was based on the shape and size of 50 conidia and appressoria. Length and width measurements were obtained through images captured by a digital camera attached to an optical microscope with a 400x magnification, using Cellsenses Standard software. Mycelial growth of Colletotrichum tropicale was analyzed. in Petri dishes containing PDA medium supplemented with the following chemicals: mancozeb (240g); methyl thiophanate (45 g.L-1) and essential oils: lemongrass, citronella and mint essential oil (0.75; 1.5; 2.25 and 3%) and ADE for all controls. The selected in vitro treatments were used in the in vivo experiment, applied 72 and 48 hours before inoculation of the pathogen (resistance inducer) and 72 and 48 hours after inoculation (dressing), for the first experiment. In the second experiment, citronella and mint oils (0.25; 0.5; 0.75 and 1%) and methyl thiophanate (45 g.L-1) were used, separately, 72 and 48 hours before inoculation (inducing resistance) and 72 and 48 hours after inoculation (dressing). The inflorescences were submitted to inoculation with the pathogen, through the spraying method (106 con./mL). After 4 days, the index and severity and incidence of the disease were determined using a rating scale. The species C. orchidearum, C. siamense, C. tropicale, C. fructicola and C. theobromicola are associated with anthracnose in flowers of Emperor's Cane, Anthurium and Alpinia in Northeast Brazil. The essential oils showed efficiency in the reduction of anthracnose (C. tropicale) in Emperor's Bastion. Keywords: cut flower, inflorescence, post-harvest, disease fungus.