Pathogenicity and characterization of Thielaviopsis ethacetica in oil palm

ABSTRACT

Thielaviopsis paradoxa is a soilborne fungal pathogen widely distributed worldwide and capable of infecting a wide range of hosts. In oil palm, it is the etiological agent of basal rot, an important disease that can cause serious damage due to its severity and the rapid dispersion of the pathogen. This study evaluated the pathogenicity and characterized an isolate of Thielaviopsis sp. in oil palm. The isolate was obtained from the stem of an oil palm plant with apparent rot symptoms. Pathogenicity was evaluated in two oil palm cultivars, the interspecific hybrid Manicoré and the intraspecific hybrid Tenera. Seedlings were inoculated by conidial suspension at 1x10⁷ conidia per milliliter e mycelial disks, with and without injuries in the leaf rachis. The isolate was grown in PDA culture medium for morphological characterization. Phylogenetic analysis was performed based on comparison of sequences from the EF-1? and ITS regions with sequences available from GenBank-NCBI and analyzed in Mega 6.0. The isolate was pathogenic to the two oil palm cultivars in previously injured seedlings, causing symptoms of brown rot and formation of a yellowish halo in the rachis. As the disease progressed, the leaves showed yellow coloration and dried, resulting in broken rachis. The isolate of Thielaviopsis sp. showed rapid growth with mycelial growth rate of 50.76 mm day^-1, covering the 90-mm Petri plate within two days. The colony, initially white, became black with sporulation and produced two types of conidia: endoconidia and aleuroconidia. After phylogenetic analyses, the species Thielaviopsis ethacetica could be proven as the etiological agent of the dry basal rot of oil palm and could be distinguished from T. paradoxa.

Keywords
Thielaviopsis ethacetica ; Phylogeny; Elaies spp.