Water management
Root infection and yield loss caused by M. graminicola on rice can be greatly reduced with appropriate management of irrigation water. M. graminicola is unable to penetrate rice roots under anaerobic soil conditions; thus maintaining flooded soils, especially early in the season, is an effective means of controlling this nematode. In pot studies, flooding from tillering stage through booting stage significantly reduced M. graminicola damage and increased yields (14).

Crop rotation
Rotating fields out of rice is not a viable control option for M. graminicola in Asia. However, crop rotation with cowpea in an upland system (9), and with mustard in a deepwater rice system (8) greatly reduced soil M. graminicola population levels, though with no significant effect on yield. Quantifying the host status of rice rotational crops is important for determining which alternate crops to use in a rotation with rice for effective management of M. graminicola. In South Asia's rice-wheat system, many of the crops rotated with rice, including wheat, sugarcane, mungbean, and mustard, are alternate hosts to this nematode (5), thus limiting the effectiveness of crop rotation as a management option for this system.

Plant breeding
To date, no root-knot nematode resistance gene has been identified in Oryza sativa germplasm. However, there is research underway at the International Rice Research Institute to transfer resistance to O. sativa through crosses with O. longistaminata and O. glabberrima, two West African species which show resistance to M. graminicola (13).

Biological control
Only limited studies have been done on biological control of this nematode. Infection of M. graminicola juveniles by Pasteuria penetrans significantly decreased root invasion and reduced gall formation on tomato (1, 3). Spore burdens greater than 11 per M. graminicola J2 were needed to achieve effective control, and soil temperatures above 30¡ C promoted greater P. penetrans infection of M. graminicola as compared to 20¡ C (1, 3). Galling severity on rice roots was reduced by half, and yields nearly doubled, by coating rice seeds with a suspension of Paecilomyces lilacinus or Gliocladium virens (2), suggesting that these antagonist fungi may be effective biocontrol agents. However, achieving effective biological control in production fields has generally been poor and inconsistent because competition and predation on the introduced agent by other soil microorganisms, and due to adverse soil physical and chemical conditions. Biocontrol strategies that utilize endophytic nematode antagonsists avoid many of the problems associated with introducing biocontrol organisms to bulk soil (12).

Significant reductions of plant-parasitic nematode populations have been achieved by incorporation of organic amendments. Substances with a low carbon to nitrogen ratio, such as leguminous green manures and oilcakes, produce a rapid increase in soil ammonia which is toxic to the nematode, and they stimulate growth and activity of nematode-antagonistic or predatory microorganisms (15). Effective control of nematode and fungal pathogens has also occurred with soil incorporation of Brassica and Sorghum spp. green manures, which produce isothiocynate and hydrogen cyanide compounds, respectively, during plant decomposition. However, the quantity of incorporated material needed to achieve effective nematode control is often not agronomically feasible, and the production of cyanogenic compounds can vary widely among cultivars of a green manure species (4, 6, 16). Moreover, biofumigation can negatively impact fungi that are antagonistic to plant-parasitic nematodes (11).


Nematicides
Furadan 5G and F\furadan 3G effectively suppressed M. graminicolain field studies in Bangladesh and Thailand. Soil drenching with fensulfothion or carbofuran (1 kg a.i. ha-1) is recommended for control of M. graminicola in rice-wheat cropping areas of South Asia (10). Seed soaking in carbosulfan, monocrotophos, triazophos, and phosalone were also reported to effectively reduce galling by M. graminicola(7). However, nematicides are expensive and highly toxic, and their regulation has limited the options for chemical control.

References
1. Ahmed R, Gowen S. 1991. Studies on the infection of Meloidogyne spp. with isolates of Pasteuria penetrans. Nematologia Mediterranea 19: 229-33.

2. Debanand D, Saikia M, Sarmah D, Das D. 1999. Comparative efficacy of botanicals and antagonistic fungi for the management of rice root-knot nematode, Meloidogyne graminicola. International Journal of Tropical Agriculture 17: 287-90.

3. Duponnois R, Netscher C, Mateille T. 1997. Effect of the rhizosphere microflora on Pasteuria penetrans parasitizing Meloidogyne graminicola. Nematologia Mediterranea 25: 99-103.

4. Kirkegaard JA, Sarwar M. 1998. Biofumigation potential of brassicas. Plant and Soil 201: 71Ð89.

5. MacGowan JB, Langdon KR. 1989. Hosts of the rice root-knot nematode Meloidogyne graminicola. Nematology Circular, Fla. Dept. Agric. &. Consumer Serv. No. 172.

6. Mojtaedi H. 1993. Managing Meloidogyne chitwoodi on potato with rapeseed as green manure. Plant Disease 77: 42-6.

7. Rahman M, Das P. 1994. Seed soaking with chemicals for reducing infestation of Meloidogyne graminicola on rice. Journal of the Agricultural Science Society of North East India 7: 107-8.

8. Rahman ML. 1990. Effect of different cropping sequences on root-knot nematode, Meloidogyne graminicola, and yield of deepwater rice. Nematologia Mediterranae 18: 213Ð7.

9. Roder W, Keoboulapha B, Phengchanh S, Prot JC, Matias D. 1998. Effect of residue management and fallow length on weeds and rice yield. Weed Research 38: 167-74.

10. Sharma SB, Rahaman PF. 1997. Nematode Pests in Rice and Wheat Cropping System in the Indo-Gangetic Plain. Presented at Nematode Pests in Rice-Wheat-Legume Cropping Systems, Proceedings of a Regional Training Course, Haryana, India.

11. Schuster RP, Over B, Sikora RA. 1998. Potential and diversity of egg pathogenic fungi of cyst nematodes in monoculture fields. Mededelingen Faculteit Landbouwkundige en Toegepaste Biologische Wetenschappen Universiteit Gent 63: 641-8

12. 2. Sikora RA. 1997. Biological system management in the rhizosphere an inside-out/outside-in perspective. Mededelingen Faculteit Landbouwkundige en Toegepaste Biologische Wetenschappen Universiteit Gent 62: 105-12

13. Soriano IR, Schmit V, Brar DS, Prot JC, Reversat G. 1999. Resistance to rice root-knot nematode Meloidogyne graminicola identified in Oryza longistaminata and O. glaberrima. Nematology 1: 395-8.

14. Soriano IRS, Prot JC, Matias DM. 2000. Expression of tolerance for Meloidogyne graminicola in rice cultivars as affected by soil type and flooding. Journal of Nematology 32: 309-17.

15. Stirling, GR. 1991. Biological Control of Plant Parasitic Nematodes: Progress, Problems, and Prospects. UK: CAB Int. 282 pp.

16. Widmer TL, Abawi GS. 2002. Relationship between levels of cyanide in Sudangrass hybrids incorporated in soil and suppression of Meloidogyne hapla. Journal of Nematology 34: 16-22.