First report of a 16SrXI Group phytoplasma (Candidatus Phytoplasma oryzae) associated with Napier grass stunt disease in Uganda

Napier grass (Pennisetum purpureum), also known as elephant grass, is an important fodder crop in Uganda. The forage has been increasingly used in intensive (zero grazing) and semi-intensive dairy cattle production systems, in order to meet the increasing demand for milk in Uganda. Napier grass stunt disease, causing short internodes, bushy appearance, yellow to purple streaking and a low biomass yield, has spread among smallholder dairy farmers in Uganda since it was first observed in 2001 (Alacai et al., 2004). The disease has also been reported from western Kenya and shown to be associated with a phytoplasma (Jones et al., 2004) and in Tanzania (B. Pallangyo, pers. comm).

Leaf samples of stunted Napier grass were collected in the three major Napier grass-growing areas of Uganda. Air-dried leaf samples were ground in liquid nitorhen and total DNA was extracted using a DNeasy kit according to manufacturer’s instructions (Qiagen, Hilden, Germany). Leaves without symptoms were used as negative control. The presence of phytoplasma in plants with symptoms was confirmed by a real-time PCR method according to Christensen et al. (2004). Seven of these positive samples were sequenced in the 16S rRNA gene (deposited in Genbank as Accession EF012650) and the 16S/23S intergenic spacer (Accession No. EF012649). No sequence variation was found. The sequences were 99.3% identical to the 16S rRNA sequences from the phytoplasma associated with Napier grass stunt from Kenya, which belongs to the 16SrXI rice yellow dwarf group (Candidatus Phytoplasma oryzae; Jones et al. 2004). This is the first report of a 16SrXI Group phytoplasma associated with Napier grass stunt disease in Uganda.