Characterizing the Palm Pathogenic Thielaviopsis Species from Florida

Area of Science:

• Plant Pathology
• Mycology
• Fungal Genetics

Background:

• Thielaviopsis paradoxa sensu lato causes destructive Thielaviopsis trunk and heart rot in palms, leading to sudden collapse and posing risks to life and property.
• Existing knowledge of the Thielaviopsis infection process in palms is limited, with no characterization of the T. paradoxa species complex within the United States.

Purpose of the Study:

• To characterize Thielaviopsis paradoxa sensu lato isolates obtained from diseased palms in Florida.
• To investigate the genetic diversity, growth characteristics, pathogenicity, and fungicide sensitivity of different T. paradoxa clades.

Main Methods:

• Multi-locus phylogenetic analysis using ITS, β-tubulin, and tef1-α gene sequences.
• Assessment of colony morphology and growth rates across different media and temperatures.
• Pathogenicity assays on whole plants and evaluation of fungicide sensitivity.

Main Results:

• Phylogenetic analysis resolved isolates into two distinct clades: one identified as Thielaviopsis ethacetica and another potentially representing an undescribed species.
• Differential growth rates and colony morphologies were observed between the clades at varying temperatures, with T. ethacetica thriving at 35°C and the other at 10°C.
• T. ethacetica demonstrated higher pathogenicity, causing larger lesions on wounded palm leaflets, and exhibited an unequal distribution of mating-type alleles.

Conclusions:

• The study confirms the presence of at least two distinct Thielaviopsis clades infecting palms in Florida, including T. ethacetica and a potential new species.
• Significant variations in growth, pathogenicity, and fungicide response exist between these clades, necessitating tailored management strategies.
• Further targeted sampling across US palm-growing regions is crucial to fully understand the diversity of Thielaviopsis species and their impact on palm health.