Detached leaflet assay for palms identifies variable disease resistance to Thielaviopsis species

Authors: AYIKA, MARIE-GABRIELLE - Miami Dade University; BANSAL, KAMALDEEP - Oak Ridge Institute For Science And Education (ORISE); ROSANO, AVRIL - Oak Ridge Institute For Science And Education (ORISE); CHAKRABARTI, SEEMANTI - Oak Ridge Institute For Science And Education (ORISE); Nageswara Rao, Madhugiri; Singh, Sukhwinder; DHILLON, BRAHAM - University Of Florida

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2025
Publication Date: 9/18/2025
Citation: Ayika, M., Bansal, K., Rosano, A., Chakrabarti, S., Nageswara Rao, M., Singh, S., Dhillon, B. 2025. Detached leaflet assay for palms identifies variable disease resistance to Thielaviopsis species. Plant Disease. https://doi.org/10.1094/PDIS-07-25-1577-RE.
DOI: https://doi.org/10.1094/PDIS-07-25-1577-RE

Interpretive Summary: Establishing whether a fungal species is a pathogen on a given plant host is contingent upon its ability to colonize and cause disease. In order to identify a fungal pathogen, a healthy plant is exposed to fungal inoculum under environmental conditions conducive for fungal growth and disease establishment, and the plant is monitored for symptom development. To address challenges associated with laborious whole-plant trials, we present the first application of a detached leaflet assay to quantitatively evaluate disease resistance to Thielaviopsis ethacetica across the Arecaceae. Our objectives were to, i) compare the pathogenicity of different Thielaviopsis species, ii) characterize host response profiles, and iii) quantify both inter- and intra-specific variation in susceptibility under controlled conditions. Using T. ethacetica inoculum, a total of 262 individuals representing 29 species across 17 genera were screened. Lesion measurements revealed clear species-level differences as well as significant varietal variation among palms. This detached leaf assay enables high-throughput, reproducible pathogenicity screening, allowing for the rapid identification of susceptible and resistant germplasm. By facilitating detailed assessment of Thielaviopsis–palm interaction, this approach serves as a valuable tool for informing targeted breeding efforts and guiding germplasm conservation strategies aimed at mitigating impact of palm diseases.

Technical Abstract: Thielaviopsis paradoxa species complex comprises of fungal pathogens that cause both bud (heart) and trunk rot of palms. Thielaviopsis spp. are soil borne pathogens that infects all plant parts, i.e., roots, stem, leaves, and fruits, of primarily monocot hosts including palms, banana, sugarcane, and pineapple. However, very little is known about the T. paradoxa species complex in the US and the palm - Thielaviopsis pathosystem. Our previous analysis showed that the T. paradoxa complex is comprised of at least two species in Florida, T. ethacetica and a novel, undescribed Thielaviopsis species. In order to study the interaction, a detached leaflet assay for palms was established to test the pathogenicity of the species in T. paradoxa complex. Lesion size was measured quantitatively and used to assess pathogenicity of the fungal isolates as well as host response. Wounding the detached leaflets promoted lesion development, and disease symptoms were similar to whole plants. A comparison of the two Thielaviopsis species showed that all T. ethacetica isolates consistently produced larger lesions and were more aggressive than the undescribed Thielaviopsis species in detached leaflet assay on foxtail palms (Wodyetia bifurcata). Subsequently, T. ethacetica was used to screen 262 individuals from 29 species across 17 genera of palms using the detached leaflet assay. Lesion development in individuals from at least five palm species across four genera was significantly different from the negative control suggesting that these palm species maybe susceptible to T. ethacetica. Additionally, variation in lesion development was also observed at varietal level in coconut palms. This detached leaflet assay would facilitate dissection of the Thielaviopsis - palm interaction and as well as accelerate screening of palm germplasm repositories to identify sources of resistance to Thielaviopsis.