EFFECT OF ESSENTIAL OILS AND TECHNICAL CASHEW NUT SHELL LIQUID ON THE DEVELOPMENT OF COLLETOTRICHUM GLOEOSPORIOIDES ISOLATED FROM CARICA PAPAYAS

Brazil ranks among the largest producer and exporters of papaya (Carica papaya L.) worldwide. However, the fruit high metabolic activity during post-harvest phase leads to a rapid maturation and short lifespan, enhancing the liability of fungus infection. Anthracnose is a great concern disease, mainly considering post-harvest phase, caused by the fungus Colletotrichum gloeosporioides, which is able to infect the immature green fruit and remains in a latent stage, without any evident symptoms until reached the right conditions for infection. Therefore, the increasing on demand for products with less application of agrochemical reflects on a greater necessity of alternative methods. Therefore, the essential oils are potential alternatives due to their low environmental disturbance and the control activity on microorganisms, through releasing chemical compounds from secondary metabolism, which in turn, do not have the deleterious effects associated to agrochemicals. The antimicrobial activity of the technical cashew nut shell liquid (tCNSL) has been reported due to the presence of chemical compounds and anacardic acid content. The aim of this study was to evaluate the fungicidal potential of tCNSL pure and diluted in potassium, sodium hydroxide and organic base, as well as essential oils of Clove (Syzygium aromaticum), Babaçu palm (Attalea speciosa), peppermint (Mentha piperita) and of Tea tree (Melaleuca alternifolia) on conidia germination and mycelial strain of C. gloeosporioides isolated. The fungi samples were obtained from lesions caused by anthracnose in papaya at maturation states 4 and 5. Small lesions were used for direct plating on Potato Dextrose Agar (PDA) and incubated in a BOD for seven days at 29°C. The fungi were isolated after successive subcultures, purified and stored at -20°C in a PDA with added 40% glycerol. In order to confirm the presence of conidia and appressoria, the structures corresponding to the species, a microculture technique was carried out. In order to asses the fungicidal activity, the tests were carried out considering the protocol established by the Clinical and Laboratory Standards Institute (CLSI) 2008, by the Minimum Inhibitory Growth (MIC) assessment method. At first, 23 inoculums of the papaya were obtained, from which along the replications, 2 of these inoculums were separated and exhibited the structures corresponding to C. gloeosporioides. The inhibitory efficiency was heterogeneous concerning the concentrations, however, the results show a clear inhibition of conidia germination compared to the fungicide used as a control. Furthermore, in some treatments, despite the mycelial growth, there was no evidence of spore development. The peppermint and Melaleuca oil exhibited inhibition effects beyond 50% at concentrations higher than 250μl. The Babaçu palm oil inhibited the growth of the isolate 10 by above 75% at the average concentrations of 62.5 and 31.25μl. However, the inhibition of inoculum 20 was not higher than 50%. The clove oil exhibited an efficient antifungal activity at all concentrations. From the tested CNSL solutions, the one treated with the inorganic base of sodium hydroxide (NaOH) showed a growth inhibition beyond 50%. The association of cardanol with NaOH causes the cell membrane to be permeable, inducing cell lysis.