A stunting syndrome of Napier grass in Ethiopia is associated with a 16SrIII Group phytoplasma

Napier or elephant grass (Pennisetum purpureum) is a perennial grass grown widely in East Africa as a fodder crop.  It is being promoted in Ethiopia for use by cut and carry (zero grazing) smallholder livestock keepers.  In Kenya, Napier grass stunt is associated with a phytoplasma belonging to the 16SrXI (Candidatus Phytoplasma oryzae) group.  The impact of Napier stunt is such that the viability of the smallholder dairy industry in Western Kenya is seriously threatened by this disease (Jones et al., 2004).  The International Livestock Research Institute (ILRI) in Ethiopia maintains a germplasm collection of Napier at its field stations in Debre Zeit and Zwai, under the auspices of FAO as a global public good.  In 2004 symptoms were observed of stunting in some of the accessions and a phytoplasma infection was suspected.  Leaf samples of healthy and affected Napier were collected from Debre Zeit and Zwai and the DNA extracted.  This was used as a template for nested PCR analysis using primers P1/P7 and R16F2n/R16R2 (Arocha et al., 2005), and bands of the expected size (1.25kb) were produced in 8/11 diseased and 3/9 apparently healthy samples.  These amplicons were sequenced directly, the sequences aligned, subjected to BLAST analysis and deposited in GenBank (Accession No. DQ305977).  The highest similarity was with the African sugarcane yellow leaf phytoplasma (Accession No. AF056095), a member of the 16SrIII (Candidatus Phytoplasma pruni) group (IRPCM Phytoplasma/Spiroplasma Working Team–Phytoplasma taxonomy group, 2004) but not to the Napier grass stunt phytoplasma found in Kenya (GenBank Accession No. AY736374) or others of the 16SrXI group.  Latent infection by phytoplasmas has previously been reported for yellow leaf syndrome of sugarcane in South Africa (Cronjé et al.,1998) and in Cuba for sugarcane and weeds (Arocha et al., 2005).  This is the first report of a 16SrIII group phytoplasma infecting Napier grass.