'Candidatus Phytoplasma oryzae', a novel phytoplasma taxon associated with rice yellow dwarf disease

Abstract

In addition to rice yellow dwarf (RYD) phytoplasma, several phytoplasmas infect gramineous plants, including rice orange leaf, bermuda grass white leaf, brachiaria grass white leaf and sugarcane white leaf phytoplasmas. To investigate whether the RYD phytoplasma is a discrete, species-level taxon, several isolates of the aforementioned phytoplasmas were analysed using PCR-amplified 16S rDNA sequences. Two RYD isolates, RYD-J T and RYD-Th, were almost identical (99?2 %), but were distinct (similarities of 96?3-97?9 %) from other phytoplasma isolates of the RYD 16S-group. The notion that the RYD phytoplasma constitutes a unique taxon is also supported by its unique insect vector (Nephotettix sp.), its unique host plant in nature (rice) and its limited geographical distribution (Asia). In Southern blot analysis, chromosomal and extrachromosomal DNA probes of the RYD phytoplasma reportedly did not hybridize with those of closely related phytoplasmas. These properties of the RYD phytoplasma clearly indicate that it represents a novel taxon, 'Candidatus Phytoplasma oryzae'.Rice yellow dwarf disease continues to be a problem for rice farmers in many regions of Asia. Infected rice (Oryza sativa) turns pale yellow and gradually starts to decay; it ultimately shows stunted growth and fails to produce grain. For many years after its discovery in 1919 (Anonymous, 1919), the agent that caused this disease was unknown and was believed to be a virus, until it was identified as a phytoplasma (then called a mycoplasma-like organism) (Nasu et al., 1967). The causative agent, RYD phytoplasma, is transmitted by the leafhoppers Nephotettix cincticeps, Nephotettix virescens and Nephotettix nigropictus, and is present in most rice-growing countries in Asia (Ou, 1985;. From its 16S rDNA sequences, geographical distribution and the specificity of its host and insect vector, RYD phytoplasma has been regarded as an independent taxon by Namba et al. (1993a) and .RYD phytoplasma has been classified in the RYD 16S-group (Jung et al., 2003). Its closest known relatives, based on 16S rDNA phylogenetic analyses, are the phytoplasmas associated with sugarcane white leaf (SCWL) and sugarcane grassy shoot (SCGS) found in sugarcane (Saccharum officinarum), annual bluegrass white leaf (ABGWL) found in annual bluegrass (Poa annua), bermuda grass white leaf (BGWL) in bermuda grass (Cynodon dactylon) and brachiaria grass white leaf (BraWL) in brachiaria grass (Brachiaria spp.) (Schneider et al., 1995; Nakashima et al., 1996;Lee et al., 1997; Wongkaew et al., 1997;Tran-Nguyen et al., 2000). Although these phytoplasmas have many traits in common, such as symptoms (leaf chlorosis and proliferation of tillers in most cases) and host plants (gramineous plants), they have not been characterized in detail and little is known of the variability of the group. To determine whether RYD phytoplasma constitutes a discrete, coherent taxon, RYD isolates from two different areas, Japan and Thailand, were analysed and compared with other phytoplasmas studied to date.R...

Diversity of Bacterial Endosymbionts Associated with Macrosteles Leafhoppers Vectoring Phytopathogenic Phytoplasmas

“…Alternatively, the PCR primers may not match with 16S rRNA gene sequences of Phytoplasma. Sequencing and phylogenetic analysis of the PCR products identified two genetically distinct Phytoplasma strains: a strain (here designated Phytoplasma AY) that belongs to the clade of "Candidatus Phytoplasma asteris," known to be associated with aster yellows and related plant diseases (71), and another strain (here designated Phytoplasma RYD) that clusters with "Candidatus Phytoplasma oryzae," known to be associated with rice yellow dwarf disease (72) (Fig. 4).…”

‘Candidatus Phytoplasma’, a taxon for the wall-less, non-helical prokaryotes that colonize plant phloem and insects

“…Phytoplasma ziziphi' (Jung et al, 2003a), 'Ca. Phytoplasma oryzae' (Jung et al, 2003b) and 'Ca. Phytoplasma ulmi' (Lee et al, 2004b), but a general description of the comprehensive taxon 'Ca.…”

Group 16SrXI phytoplasma strains, including subgroup 16SrXI-B and a new subgroup, 16SrXI-D, are associated with sugar cane white leaf

“…To date, three subgroups of the 16SrXI group have been designated, 16SrXI-A (Rice yellow dwarf, RYD), 16SrXI-B (SCWL) and 16SrXI-C (Leafhopper-borne, BVK) (Jung et al, 2003;Lee et al, 1997Lee et al, , 1998Madhupriya et al, 2015;Namba et al, 1993). Previously, only the 16SrXI-B subgroup was reported to be associated with SCWL (Lee et al, 1998).…”