RESUMO
Lethal bronzing (LB) is a fatal infection that affects over 20 species of palms (Arecaceae) and is caused by the phytoplasma 'Candidatus Phytoplasma aculeata'. This pathogen causes significant economic losses to landscape and nursery companies in Florida, USA. Recently, the vector was determined to be the planthopper Haplaxius crudus, which was more abundant on LB-infected palms. Herein, the volatile chemicals emitted from LB-infected palms were characterized using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME/GC-MS). Infected Sabal palmetto were identified and confirmed as positive for LB via quantitative PCR. Healthy controls of each species were selected for comparison. All infected palms exhibited elevated levels of hexanal and E-2-hexenal. Threatened palms showed high releasing concentrations of 3-hexenal and Z-3-hexen-1-ol. The volatiles characterized herein are common green-leaf volatiles (GLVs) emitted by plants under stress. This study considers the first documented case of GLVs in palms attributed to phytoplasma infection. Due to the apparent attraction of LB-infected palms to the vector, one or several of the GLVs identified in this study could serve as a lure for the vector and supplement management programs.
RESUMO
Lethal bronzing (LB) is a fatal palm disease caused by the phytoplasma 'Candidatus Phytoplasma aculeata'. This disease causes significant economic losses in palm industries and landscapes. The American palm cixiid, Haplaxius crudus, recently was identified as the vector of the phytoplasma. However, knowledge about LB phytoplasma transmission is limited due to the lack of a method to generate phytoplasma-infected insects in the laboratory. In this study, the acquisition and transmission of the LB phytoplasma by H. crudus were investigated. Successful acquisitions of the phytoplasma by H. crudus were observed at 2 days acquisition access period on LB-infected palm spear leaves. Analyses revealed increased phytoplasma infection rates of H. crudus with longer acquisition access periods and latent periods. A significantly higher phytoplasma infection rate was shown after various acquisition access periods and latent periods than the infection rate of the field-collected H. crudus population. Transmission of the phytoplasma from LB-infected spear leaves to sucrose media by H. crudus also was observed using digital PCR assays. These results further support the vector status of H. crudus and offer valuable information to understand LB phytoplasma transmission. Additionally, these results generate a critical baseline for future LB phytoplasma-vector research by providing a way to generate vectors with high phytoplasma infection rates in the laboratory setting.
