Abstracto
- Late blight disease caused by the plant pathogen Phytophthora infestans is one of the major threats for tomato crops in Colombia. All tomatoes grown in Colombia are susceptible to this disease and control requires a high input of fungicides. Knowledge on the population structure of P. infestans is important to determine if there are changes in the sensitivity to fungicides. However, information on the population structure of P. infestans on tomato crops in Colombia is limited. Here, we characterized the genotypic and phenotypic diversity of 22 isolates of P. infestans. collected in the departments of Antioquia, Boyacá, Caldas, and Cundinamarca. The genotypic diversity was assessed using microsatellite markers and mitochondrial haplotyping. Furthermore, sensitivity to three systemic fungicides (mefenoxam, cymoxanil, and fluopicolide) was evaluated. Mitochondrial haplotyping showed that in Colombia isolates of P. infestans collected on tomato are Ia and Ib, while isolates collected on potatoes are IIa. Microsatellite analysis showed that isolates from tomato form two groups: one including isolates of the Ib mitochondrial haplotype of the US-1clonal lineage and the other one including isolates of the Ia haplotype related to 40 US-22 lineage. Furthermore, differences in sensitivity to fungicides were observed. Eighty one percent of the P. infestans isolates were resistant to mefenoxam with an EC50 value greater than 10 µg ml-1 . Forty-four percent of the isolates showed an intermediate resistance to cymoxanil. The EC50 value ranged between 1 to 10 µg ml-1. In the case of fluopicolide, 93% of the isolates were sensitive with EC50 values less than 1 µg ml-1. Alternative control of late blight using silicon was successful using an in vitro assay. However, it is necessary to test its efficacy in vivo. The information obtained in this study allows to establish the 3 actual state of P. infestans populations associated to tomato crops in Colombia. This information will help optimize the use of fungicides and will contribute to broader studies on the diversity of this plant pathogen.
