First report of the root-knot nematode (Meloidogyne graminicola) in Madagascar rice fields
Rice is the major crop produced in Madagascar and is infested by numerous plant-parasitic nematodes. An extensive list of plant-parasitic nematodes found in association with rice roots during a survey of 14 sites is presented. This is the first time that Meloidogyne graminicola has been detected in Madagascar, which is relevant information for future management of this economically important nematode pest of rice.
KeywordsRice Plant parasitic nematode Galls Meloidogyne graminicola
Rice (Oryza sativa) is an essential food crop for a significant majority of the world’s human population. Various pests and diseases constitute important constraints to successful crop production, and these include the plant-parasitic nematodes (PPN) that account for great crop-yield losses (Mantelin et al. 2016). Among the PPN, root-knot nematodes (genus Meloidogyne) are considered to be the most damaging genus for numerous agricultural crops (Mantelin et al. 2016). In Asia, Meloidogyne graminicola is recognized as one of the most important pests of rice.
Having an extensive distribution map of M. graminicola can be useful for future management strategies since synthetically-derived nematicides commonly used to control nematode pests are being continuously withdrawn from world markets (MBTOC 2010). Proper information on the nematodes present in the rice paddy is necessary before developing any environmentally sustainable management strategies. The purpose of this note is to report for the first time the presence of the rice root-knot nematode M. graminicola in Madagascar.
All PPN were then identified at the genus level by PCR followed by sequencing using ITS-1 amplification of rDNA genes as described previously in Bellafiore et al. (2015). For each individual PPN, the sequences were compared to other deposited ITS sequences in the GenBank database using standard nucleotide BLAST in April 2016. When a positive match to M. graminicola was observed, we confirmed the identification of this species using the SCAR-MgFw/Rev primers (Bellafiore et al. 2015) and the mitochondrial DNA marker 94R (Besnard et al. 2014). DNA amplicon obtained from mitochondrial DNA using the 94R primers was then subsequently gel-purified and sequenced as described above with the primer 94R-Fw (5′-GAATGAAAACGATCAGAGACATG-3′).
The 14 sites sampled, and their GPS coordinates (using the Geodetic Reference System WGS 84)
Both M. graminicola populations as well as the two M. graminicola related species identified in this survey were isolated from fields present in the South East region of Antsirabe. In this region, rice is mainly grown under lowland and irrigation conditions, two water regimes favourable to M. graminicola that could explain the presence of this species in this part of the island. To our knowledge, this report represents the first record of M. graminicola on rice in Madagascar and Africa. As mentioned above, M. graminicola has only been found once in South Africa (Kleynhans 1991) but this was on another plant host and in other environmental conditions. We hereby propose a possible hypothesis: rice in Madagascar is likely to have come from South East Asia and not from Africa since the first Malagasy people migrated from SE Asia (Indonesia and Malaysia: Dewar and Wright 1993; Perrier de la Bâthie 1931) bringing with them their homeland crops. Moreover, these would have been distributed from the eastern coast ports (S. Andrianasetra, pers. observ.) where we also found M. graminicola. More genetic population studies and surveys in Madagascar and Africa are required to confirm or infirm this hypothesis.
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