Identification of potential vectors and alternative plant hosts for the phytoplasma associated with napier grass stunt disease in Ethiopia

Napier grass (Pennisetum purpureum), the most important forage crop in East Africa, has recently been affected by a devastating disease named Napier Grass Stunt (NGS). A phytoplasma of group 16SrI has been associated with NGS in Kenya and Uganda, whereas in Ethiopia, group 16SrIII was previously identified in NGS affected fields. However, no insect vectors or alternative hosts have been recorded for NGS in East Africa. During 2005, surveys were conducted at NGS-affected plantations of Debre-Zeit and Zwai field stations in Addis Ababa. Leaf samples were collected from weeds located in and surrounding the NGS-affected areas. Leafhopper species were also surveyed by vacuum sampling in a search for natural phytoplasma vectors. Total DNA was extracted from plants and insects, and used as a template in nested polymerase chain reaction (nPCR) with universal 16S rRNA phytoplasma primers. Restriction fragment length polymorphism (RFLP), sequencing of PCR products and phylogenetic analysis were conducted for a finer identification and characterization of the phytoplasma associated with NGS. A 16SrIII-A phytoplasma with 100% of identity in the 16S rRNA sequence with that of the previously identified one in Napier Grass (DQ305977) was identified from alfalfa, Medicago sativa (DQ305982), Cynodon dactylon (accession no. DQ3058983), Exitianus sp. (DQ305980) and Leptodelphax dymas collected in Debre Zeit (DQ305979) and Zwai (DQ305978). These findings suggest that M. sativa and Cy. dactylon are alternative reservoirs, and Exitianus sp. and L. dymas, potential vectors of the 16SrIII-A phytoplasma, which may have epidemiological implications in spreading NGS in Ethiopia.