Genetic characterization of Moniliophthora perniciosa from Ecuador and in vitro sensitivity to compost tea

Abstract

Moniliophthora perniciosa is the causal agent of the witches’ broom disease (WBD) in cacao but the morphological and molecular diversity of M. perniciosa in Ecuador—the top fine flavor cacao producer worldwide—are poorly understood and the pathogen’s sensitivity to compost teas is unknown. A total of 90 isolates of M. perniciosa were obtained from symptomatic samples of cocoa branches and pods collected from four cocoa-producing regions of Ecuador. Growth of each isolate was assed and fitted to a Gompertz model, and the molecular variability was evaluated by sequencing the ITS1, 5 .8s, and ITS2 rDNA regions as well as by inter-retrotransposon amplified polymorphism (IRAP), retrotransposon microsatellite amplified polymorphism (REMAP), and simple sequence repeats (SSR) analyses. Sensitivity of M. perniciosa to a compost tea was evaluated at concentrations of 0.5, 1, 1.5, 2, 2.75, and 3.5% in PDA. Results showed morphological and growth rate homogeneity across isolates. Mycelial growth fitted to Gompertz model gave similar parameter estimates for isolates from the different sampling sites. No molecular variability was observed based on ITS and SSR analysis but IRAP and REMAP tests showed high polymorphism. The total genetic diversity based on IRAP and REMAP tests was 0.28 and the genetic diversity within population was 0.24, with Nei’s diversity, Shannon’s Information, and percent polymorphism values of 0.315, 0.48, and 95.24, respectively for the whole sampled population; isolates from Los Rios province being the most polymorphic. Compost tea sensitivity analysis performed on 85 of the isolates showed a significant inhibitory effect at concentrations of 2.75% or above but concentrations below 1.5% significantly enhanced the growth of most isolates of the pathogen. Results confirmed the high genetic diversity of M. perniciosa and provided insights into growth rate and compost tea sensitivity of the pathogen in Ecuador.