Abstract
Napier grass (Pennisetum purpuruem) production for zero grazing systems has been reduced to rates of up to 90% in many smallholder fields by the Napier stunt (Ns) disease caused by phytoplasma sub-group 16SrXI in western Kenya. It is hypothesized that several other wild grasses in Kenya could be infected by phytoplasmas that would otherwise pose a significant threat to Napier, other important feeds and food crops. This study therefore sought to detect and identify phytoplasma strains infecting wild grasses in western Kenya using 16S ribosomal RNA (ribonucleic acid) gene as well as identify wild grass species hosting phytoplasmas in 646 wild grass samples that were collected in October 2011 and January 2012 during a random crossectional survey conducted in Bungoma and Busia counties of western Kenya. DNA was extracted and nested polymerase reaction (nPCR) used to detect phytoplasmas. Two sub-groups of phytoplasmas were detected in eight grass species observed to grow near infected Napier fields. Only one of the two phytoplasmas reported was related to the Ns phytoplasma. There was a strong association between proportions of phytoplasma infection and the grass species collected (p = 0.001). C. dactylon, D. scalarum, B. brizantha, poverty grass and P. maximum had high proportions of infection and were abundantly distributed in western Kenya hence considered wild phytoplasma hosts. E. indica and C. ciliaris were scarcely distributed and had low infection rates. There was statistically significant difference in proportions of infection per location of survey (p = 0.001). Phytoplasma subgroups 16SrXI and 16SrXIV were the only phytoplasma genotypes distributed among wild grasses in western Kenya. Phytoplasma subgroup 16SrXIV predominantly infects only C. dactylon and B. brizantha grasses while phytoplasma subgroup 16SrXI is broad spectrum and infects a large number of wild grasses. In general, there is a diversity of wild grasses hosting phytoplasmas in western Kenya. These host grasses may be the reason for the high rates observed in the spread of Ns disease in western Kenya by acting as reservoirs for Ns phytoplasma.
Highlights
Napier grass (Pennisetum purpuruem) is an indigenous tropical African clumping grass which grows up to 5 meters tall
This study identified phytoplasma wild host range among wild grasses and there genotypic distribution in western
This study did not identify any novel phytoplasma strain (16S rRNA group/ subgroup) from all the sequences characterized since the divergence of all the phytoplasma sequences retrieved in this study (Table 2) was below the recommended threshold of 97.5% sequence similarity used in defining a novel phytoplasma species falling within the provisional status ‘Candidatus’ as per the International Research Program on Comparative Mycoplasmology [15]
Summary
Napier grass (Pennisetum purpuruem) is an indigenous tropical African clumping grass which grows up to 5 meters tall. It is mainly vegetatively propagated through cuttings of about 3 to 4 centimeters in length and clump splitting. Napier grass has been used by many farmers in Kenya as the major livestock feed. The increased population results in land subdivision which decreases farm size, resulting in the adoption of the zero grazing system by most farmers which uses large amounts of fodder such as napier and other wild grasses that are cut and carried home for stall feeding [3]
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