Presence of Pathogenic Fungi in Cocoa Seedlings (Theobroma cacao L.) Produced in Substrates and Soil in the Nursery

Abstract

Cocoa (Theobroma cacao L.) cultivation requires healthy, high-quality seedlings, which depends on a support material that favors seed germination and optimal, pathogen-free growth. The objective of this research was to determine the presence of pathogenic fungi in cocoa seedlings produced in the nursery in substrates and soil. The experiment was conducted from January to May 2024 at the nursery of the Mata Larga Experimental Station of the Dominican Institute of Agricultural and Forestry Research (IDIAF), in San Francisco de Macorís (SFM), Dominican Republic. A randomized complete block design (RCBD) with 12 treatments and four replications was used; the treatments combined agricultural soil, rice husk, and cattle manure in different proportions, with and without sterilization. The presence of pathogenic fungi in leaves, roots, and soil was evaluated based on seedling symptomatology, with two plants randomly selected per experimental unit (EU) in three evaluations. Fungi were identified through microscopic observation and morphological mycological keys, and the results were analyzed with descriptive statistics and frequency tables in InfoStat. Thirteen genera of pathogenic fungi were identified on leaves, among which Colletotrichum sp., Cladosporium sp., and Corynespora sp. showed the highest frequency. Pythium sp., Rhizoctonia sp., Fusarium solani, Fusarium sp., Phytophthora sp., and Papulaspora sp. were found in roots, and Fusarium sp., Trichoderma sp., Aspergillus sp., Mucor sp., and Penicillium sp. in soil and substrates. Fungal diseases could not be associated with a specific type of substrate or soil, since pathogenic fungi were present in all the treatments evaluated, although their frequency was lower in soils and roots.