Abstract
A root-knot nematode (RKN) parasitizing rice (Oryza sativa L.) and causing damage in Santa Catarina (SC), Rio Grande do Sul (RS) and Parana (PR) states (Brazil) was identified as Meloidogyne ottersoni (Thorne 1969) Franklin 1971. The species is redescribed from the Brazilian population from Meleiro (SC) and compared with the description of M. ottersoni from Wind Lake (Wisconsin, USA) with additional morphological, biochemical and molecular characterization. The female and male bear smaller stylets: 10-12 μm, 14-16 μm, respectively, when compared with M. graminicola: 12-14 μm, 16-18 μm, and M. oryzae: 14-16 μm, 18-20 μm. Meloidogyne ottersoni presents perineal patterns located on the contour of a slight protuberance. Striae are mostly continuous, never raised by transverse irregular striae, as frequently observed in M. graminicola and M. oryzae. Meloidogyne ottersoni belongs to the RKN group 11 described by Jepson (1987); the reproduction is by meiotic parthenogenesis and the somatic chromosome number is 18. The tail of second-stage juveniles is very long and thin, and tapers to a long, narrow, irregular hyaline terminus (M. ottersoni, 20.5 μm vs M. graminicola, 17.9 μm and M. oryzae, 22.0 μm, respectively). The ability of the Brazilian M. ottersoni population to parasitize canary grass, Phalaris arundinacea L. (type host), and barnyard grass, Echinocloa crus-galli, was confirmed. Biochemically, the esterase profile of M. ottersoni lacks any band (Est Ot0, Rm=0), which differentiates it from M. graminicola and M. oryzae (Est VS1, Rm=0.70 and Est O1, Rm=1.02, respectively). In Maximum Likelihood analysis of ITS, D2D3 and COXII-16S rRNA sequences, populations of M. ottersoni from different states of Brazil clustered together and were separated from other Meloidogyne spp., thus confirming that all four populations are very similar and conspecific.
Highlights
Rice (Oryza sativa L.) is the third most produced cereal worldwide, just after maize and wheat, and plays a key role in the current and future food security across the globe
The flooded rice system determines the community of plant parasitic nematodes by selecting the most adapted ones, and several authors have reported the predominance of M. graminicola Golden and Birchfield, 1965 in this cropping system (De Waele and Elsen 2007; Khan 2015)
All the populations in the Meloidogyne species complex detected on rice in Brazil (Mattos et al 2017) belong to the ‘graminis group’, which includes some species with similar characteristics: females deeply embedded in the host and body elongate with different forms, vulva situated on posterior protuberance, second-stage juveniles with hyaline part of the tail very thin and long, meiotic parthenogenesis as the mode of reproduction, males common (Jepson 1987)
Summary
Rice (Oryza sativa L.) is the third most produced cereal worldwide, just after maize and wheat, and plays a key role in the current and future food security across the globe. Several factors can interfere in rice crop yield, including nematodes. Nematodes from more than 35 genera have been reported parasitizing rice plants, but few species are described causing significant damage (Khan 2015). The flooded rice system determines the community of plant parasitic nematodes by selecting the most adapted ones, and several authors have reported the predominance of M. graminicola Golden and Birchfield, 1965 in this cropping system (De Waele and Elsen 2007; Khan 2015). All the populations in the Meloidogyne species complex detected on rice in Brazil (Mattos et al 2017) belong to the ‘graminis group’, which includes some species with similar characteristics: females deeply embedded in the host and body elongate with different forms, vulva situated on posterior protuberance, second-stage juveniles with hyaline part of the tail very thin and long, meiotic parthenogenesis as the mode of reproduction, males common (Jepson 1987)
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