Detection and Quantification of the 16SrIV-D Phytoplasma in Leaf Tissue of Common Ornamental Palm Species in Florida using qPCR and dPCR

Abstract

Lethal bronzing disease (LBD) is a lethal decline of various palm species caused by the 16SrIV-D phytoplasma. The disease was described in Texas in 2002 but found in Florida in 2006. Since its introduction, the phytoplasma has spread throughout much of the state. Typically, sampling of infected palms involves taking trunk tissue; however, in some instances this is not possible so alternative protocols are needed. In this study, phytoplasma titers were measured in different leaf tissues of infected palm in order to provide stakeholders with more sampling options. In addition, understanding the phytoplasma distribution in the palm canopy can shed light on the pathogen’s biology and aid in vector studies. Three species of palm, Phoenix roebelinii, Sabal palmetto, and Syagrus romanzoffiana, were identified and confirmed positive for infection by qPCR analysis. Leaf tissue from these species that represented different stages of decay were sampled and tested by qPCR and dPCR. For each species, phytoplasma was only detectable in the spear leaf tissue that was connected directly to the apical meristem by both qPCR and dPCR. These data are useful by demonstrating that the 16SrIV-D phytoplasma appears to be restricted to the spear leaf so stakeholders who wish to sample palms but cannot sample trunk tissue due to palm size or lack of permission to drill into the trunk have an alternative tissue type to reliably sample. In addition, this information will help improve vector research by knowing where to collect insects that have a higher probably of possessing the phytoplasma.

A Survey of Auchenorrhynchan Insects for Identification of Potential Vectors of the 16SrIV-D Phytoplasma in Florida

“…Additionally, there is a possibility that the limited detection threshold of nested polymerase chain reaction for the phytoplasma detection (Bahder et al 2018b) was unable to detect a low titer of the phytoplasma that might be present in the insects. Furthermore, there was a study that tested lethal bronzing disease phytoplasma titer of the spear leaf and non-spear leaves from 3 lethal bronzing disease infected palm species; the phytoplasma was detected only from the spear leaf but not in the non-spear leaves (Bahder et al 2019b). The unevenly distributed phytoplasma or extremely low titer of the phytoplasma in palm leaves may decrease the chance for H. crudus to acquire the phytoplasma.…”

Detection of Lethal Bronzing Disease in Cabbage Palms (Sabal palmetto) Using a Low-Cost Electronic Nose

“…The symptoms of LB are very similar to lethal yellowing (LY) [ 8 ], which includes premature fruit drop/necrosis of the inflorescence, discoloration of the oldest foliage that progresses to younger leaves over time, and finally spear leaf collapse and tree death. Traditionally, validation of infection status of LB infected palms has relied on molecular diagnostics that include quantitative PCR (qPCR) and digital PCR (dPCR) [ 9 , 10 ]. Many of the palm species affected by LB are high value, ornamental species, and given the extent of LB in Florida, economic losses to green industries are in the millions of dollars.…”