Inhibitory capacity of biological and synthetic products on the mycelial growth of the oomycete Phytophthora infestans, the causal agent of late blight

Abstract

Late blight, caused by the oomycete Phytophthora infestans, is one of the main limiting factors in potato (Solanum tuberosum L.) production in Nicaragua. The aim of this study was to evaluate the in vitro inhibitory capacity of biological and synthetic products for the management of Phytophthora infestans (Late blight). Pathogen isolates were obtained from four farms in the communities of El Robledal and El Zacatón, located in the department of Estelí, northern Nicaragua. Isolation of Phytophthora infestans from soil was carried out using baiting method, employing carnation (Dianthus caryophyllus) leaf fragments as plant bait material; subsequently, these were cultured on rye agar medium. Species-level identification was performed using morphological keys at the microscopic level. The research was experimental and conducted in the plant microbiology laboratory of the Universidad Nacional Agraria, in Managua, Nicaragua, under a completely randomized design (CRD). Four treatments were evaluated: Metalaxyl + mancozeb, copper oxychloride, Bacillus subtilis, Trichoderma sp., and an absolute control (to determine the percentage of inhibition), with six replicates per treatment, totaling 30 experimental units. The evaluated variables included identification of isolates from the potato rhizosphere, in vitro inhibitory capacity of Bacillus subtilis, copper oxychloride, and metalaxyl + mancozeb, as well as antagonistic activity of Trichoderma sp. The results of inhibitory capacity were analyzed quantitatively through percentage inhibition of radial growth and qualitatively using a five-class antagonism data using a five-class antagonism scale. Analysis of variance for inhibition percentage showed significant differences, with the most effective treatment being metalaxyl + mancozeb (88%), followed by copper oxychloride (86%). Although Bacillus subtilis and Trichoderma sp., showed lower percentage of inhibition of radial growth of Phytophthora infestans compared with synthetic products, they are classified as antifungal (in the case of Bacillus subtilis) and highly antagonistic in the case of Trichoderma sp.