Abstract
Crop protection requires the accurate identification of disease vectors, a task that can be made difficult when these vectors encompass cryptic species. Here we developed a rapid molecular diagnostic test to identify individuals of Cacopsylla pruni (Scopoli, 1763) (Hemiptera: Psyllidae), the main vector of the European stone fruit yellows phytoplasma. This psyllid encompasses two highly divergent genetic groups that are morphologically similar and that are characterized by genotyping several microsatellite markers, a costly and time-consuming protocol. With the aim of developing species-specific PCR primers, we sequenced the Internal Transcribed Spacer 2 (ITS2) on a collection of C . pruni samples from France and other European countries. ITS2 sequences showed that the two genetic groups represent two highly divergent clades. This enabled us to develop specific primers for the assignment of individuals to either genetic group in a single PCR, based on ITS2 amplicon size. All previously assigned individuals yielded bands of expected sizes, and the PCR proved efficient on a larger sample of 799 individuals. Because none appeared heterozygous at the ITS2 locus (i.e., none produced two bands), we inferred that the genetic groups of C . pruni , whose distribution is partly sympatric, constitute biological species that have not exchanged genes for an extended period of time. Other psyllid species (Cacopsylla, Psylla, Triozidae and Aphalaridae) failed to yield any amplicon. These primers are therefore unlikely to produce false positives and allow rapid assignment of C . pruni individuals to either cryptic species.
Highlights
Cacopsylla [10], due to the lack of an identification key for the genus [11]
The perfect match between microsatellite clusters, Internal Transcribed Spacer 2 (ITS2) clades and amplicon sizes demonstrates that ITS2 is a reliable marker to identify groups of C. pruni that remain evidence for successful hybridization or introgression of ITS2 alleles between the genetic groups often found in sympatry, since such events would lead to heterozygous individuals
This result indicates that the genetic groups of C. pruni constitute biological species
Summary
Cacopsylla [10], due to the lack of an identification key for the genus [11]. This difficulty becomes problematic for the pests or the vectors of plant pathogens, including Cacopsylla species that feed on fruit trees and that transmit bacteria known as phytoplasma. In their revision, Burckhardt and Hodkinson [1] estimated that. European economic entomologists have generally applied the species names, Cacopsylla pyri (Linné, 1758) and Cacopsylla pyricola (Foerster, 1848) (described as vectors of Pear decline phytoplasma in Europe and North America, respectively), to all members of the complex and have failed to recognize morphological and biological differences between the seven known species feeding on Pyrus.
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