Effectiveness of carboxylic acids from Pichia membranifaciens against coffee rust

Coffee rust is a fungal disease that has affected every coffee-producing region in the world. Given that the effectivity of the protectant and systemic fungicides applied routinely to control the spread of the causative agent of the disease (Hemileia vastatrix) has gradually diminished, besides are harmful to mammals and ecosystems, the objective of this work was to search for a mixture of harmless natural compounds with the potential to be applied in the field. So, a yeast strain producing a battery of long-chain carboxylic acids (CA) with fungicide properties was isolated from soil of coffee crop and identified as Pichia membranifaciens by ITS sequencing. Culture conditions of the yeast were optimized and the CA in the solution were characterized by Gas Chromatography-Mass Spectrometry (GC-MS) as ethyl formate (55.5 g L-1), octadecenoic acid (3.5 g L-1), propionic acid (7.2 g L-1), 3-(octadecanoyl)-propionic acid (7.2 g L-1) and methyl acetate (8.4 g L-1). Randomized field studies were conducted in three different locations in Chiapas, Mexico. Five treatments were tested including three concentrations of the CA solution (389, 584 and 778 ppm) and copper oxychloride (5 000 ppm) as conventional control. The initial coffee rust incidence averages varied between sites: Maravillas (3-9%), Santo Domingo (10-16%) and Bucaro (16-22%). The treatments of CA solution proved to be effective at slowing down the progress of the rust disease even for the sites where initial incidence was high. Likewise, the CA solution reduced the viability of H. vastatrix spores, as assessed by fluorescence microscopy.