Candidatus Phytoplasma cynodontis’: the causal agent of Bermuda grass white leaf disease

Bermuda grass white leaf (BGWL) is a destructive phytoplasmal disease of Bermuda grass (Cynodon dactylon), which is known to occur in several Asian countries, Sudan, Italy, Cuba and Australia. The causal agent, the BGWL phytoplasma, which is a member of the phylogenetic BGWL phytoplasma group or 16SrXIV group, is a discrete taxon at the putative species level, for which the name ‘Candidatus Phytoplasma cynodontis’ had previously been proposed. In advanced stages of the disease, BGWL-affected plants show a general and marked bleaching of leaves and usually die within a few months after appearance of the first symptoms. For sensitive detection of BGWL phytoplasma, polymerase chain reaction (PCR) assays using universal phytoplasma primers, all directed to rDNA, are widely employed. The BGWL pathogen can clearly be differentiated from closely related agents, which include mainly phytoplasmas infecting other gramineous species, by by restriction fragment length polymorphism (RFLP) analysis of PCR-amplified rDNA using several restriction endonucleases. Also, specific detection of BGWL phytoplasma is possible by using a reverse primer derived from the 16S-23S rDNA spacer sequence of this pathogen. Detection of BGWL phytoplasma by serological methods has also been reported. However, because serology-based techniques are less sensitive than PCR procedures, they are still not widely employed for diagnostic purposes. The use of healthy plant material and roguing of infected plants are the only measures available for reducing the incidence of BGWL phytoplasma in areas where Bermuda grass is grown as cultivated species. However, the BGWL pathogen, due to its high plant host specificity and lethal effect, may be regarded as a potential biological control agent of Bermuda grass wherever this species occurs as weed.