Óleos essenciais no controle “in vitro” de patógenos foliares associados à Carya illinoinensis

Abstract

Carya illinoinensis (Wangenh.) K. Koch, known as pecan is a native forest species from north american and was introduced in Brazil around 1915. Currently, the species is widespread mainly in the southern region of the country, where it has great economic importance. Like any crop, a pecan is subject to diseases and illnesses that can affect the viability of orchards. In recent years, scab, caused by Cladosporium spp. and a leaf spot caused by Pestalotiopsis spp. have caused damage to Brazilian orchards and so far, there are no efficient ways to control these diseases. The use of chemicals and the resulting problems triggered a search for control methods that had a reduced environmental impact. In this context, the control of pathogens through secondary compounds present in essential oils are shown as a potential form of disease control in plants. Given the above, this study aimed to evaluate the antifungal activity of essential oils of Ocimum gratissimum and Hesperozygis ringens and their effects on morphological characteristics of Cladosporium spp. and Pestalotiopsis spp., pecan leaf pathogens. For this, essential oils (EO) extracted from leaves of Ocimum gratissimum and Hesperozygis ringens suffered its components caused by gas chromatographic analysis. were transfered to Potato- Dextrose-Agar (PDA) medium, enriched with five different variations of each of the EO initially diluted in ethanol. The control consisted of PDA combined with ethanol and the positive control consisted of supplementation with Propiconazole® fungicide medium. The plates were incubated under controlled conditions (25 °C, 12h photoperiod), and the growth of the daily colonies was evaluated and after the end of the experiment, the sporulation, conidia and ramoconidia dimensions (when present), colony color and action mode of oils. At the end of the test, fungal colonies were selected for morphological characteristics responses in the scanning electron microscope (SEM). Statistical analysis was performed in a completely randomized design (CRD) with five replications. Ocimum gratissimum essential oil was mostly composed of Eugenol (86.84%), while Hesperozygis ringens the majority was Pulegone (56.72%). Both EO strongly inhibited mycelial growth of Cladosporium spp. and Pestalotiopsis spp. at concentrations 1.00 and 1.25 μL. The isolates showed mycelial growth rate, sporulation, conidia size and length influenced by at least one of the concentrations used for each EO. When comparing the OEs, there was a significant effect on some variables analyzed and the isolated factor was the most influential. In SEM, severe deformations in the fungal hyphae were observed due to membrane rupture and cytoplasm cellular extravasation. The results obtained by this work demonstrate the antifungal activity of Ocimum gratissimum and Hesperozygis ringens EO against Cladosporium spp. and Pestalotiopsis spp.