Root knot nematodes (RKN, Meloidogyne spp.) are one of the most economically genera of plant-parasitic nematodes on horticultural and field crops in temperate and tropical areas (Trudgill and Block, 2011). At a worldwide level, approximate estimates of the rice yield loss are around 10% (McGawley and Overstreet 1998), corresponding to nearly 40 million metric tons per year. Meloidogyne graminicola, also known as the Rice root knot nematode, is a telluric plant pathogen affecting rice production in all SE Asia. Several studies realized in different agrosystems of this region estimated the grain yield loss from 15 to 80%. In upland conditions and shallow intermittently flooded land, M. graminicola is the most damaging Meloidogyne species on rice (De Waele and Elsen 2007).

Rice is a staple food for over half the Earth’s population and it is particularly important in Cambodia where the rice sector represents about 15% of the country economical’s inputs. While this country offers the 9th biggest harvested paddy rice area of the world in 2013, it occupies the only the 72nd rank for rice yield with an average of 3t/Ha (FAOSTAT. Since 2004, the Cambodian government has been planning to increase rice production of 15% every year to assure local consumption (more than165kg/year/person; FAO, 2011) and exportation. Rice paddy fields production is expected to be increased by 12 Mt in 2020. However, soil texture in this country is largely covered by sandy soil that limits not only the water-holding capacity and nutrients but also gives more benefit to Root-knot nematode (RKN) infection. Indeed, 90% of rice field all over the country surveyed by our team in 2013 were infected by M. graminicola.

The study aims are: 1. Study the genetic structure of M. graminicola in SE Asia. Our preliminary results revealed an intraspecific diversity in M. graminicola species. However, available DNA markers (SCAR, ITS) are limited and the intraspecific diversity could not be correctly described. In this study, we develop new DNA markers (mitochondrial and genomic SSR and SNP) to access the diversity and the populations’ organization to further address epidemiological studies. 2. Evaluate the impact of M. graminicola on lowland and extremely poor sandy soil rice field experiment in Cambodia under different rice agro-ecosystems: Direct seeding mulch based cropping systems (DMC) vs. traditional plow based (cooperation with the Conservation Agriculture Service Center and CIRAD). The DMC systems have been introduced in a field experiment in order to improve the sandy soil quality. The DMC fields will be compared to the traditional practiced fields and to the traditional farmers’ fields outside the experiment fields. Exhaustive inventory of all PPN present in the rice root systems of growing plants in the experimental field will be done. Spatio temporal nematode survey will be conducted four times per year in order to evaluate the M. graminicola’s population dynamics. This will confirm, or not, the exclusive presence of M. graminicola as RKN in association with rice in the field. It will also offer the opportunity to identify other PPN associated with the rice root system. 3. To conduct epidemiological studies (combining the objective 1 and 2). The validated molecular markers will be used to study the M. graminicola populations’ organization inside one field. This study will allow us to answer to the following questions: Can we find distinct M. graminicola populations in one field? If so, how are they organized (distribution in the field)? Do we observe a reorganization of the populations across the time?

Partners: Stéphane Bellafiore (IRD, LMI RICE), Malyna Suong (PhD student), Rada Kong (Conservation Agriculture Service Center), Stéphane Boulakia and Florent Tivet (CIRAD, UR AIDA/CSIA)