H. RAVINDRA et al. 7 Status of Meloidogyne graminicola under different organic carbon regimes of rice growing districts of Karnataka H. Ravindra 1 , Mukesh Sehgal 2 , H.B. Narasimhamurthy 1 , K. Jayalakshmi and D.M. Soumya 1 1. Zonal Agricultural and Horticultural Research Station, University of Agricultural and Horticultural Sciences, Shimoga, 577225, Karnataka, India 2. Natinal Centre for Integrated Pest Management, LBS Building, Pusa Campus. New Delhi, 110012, India Received May 25, 2015 and Accepted August 3, 2015 ABSTRACT : Rice is grown in all the districts of Karnataka except Bangalore Urban under different agro-climatic conditions. Root-knot nematode, Meloidogyne graminicola has become a potential threat for all types of rice production systems in Karnataka. Random surveys were conducted in all the districts where rice is being cultivated. The survey revealed that all the districts are infected with rice root-knot nematodes; however, there level of incidence differs in different districts. Among the dis- tricts, more severe incidence of rice root-knot nematode was observed with root knot index of 5 in Shimoga and 4 in Chickmagalure, Mandya and Hassan districts. Moderate infection was noticed in districts viz., Davanagere, Dakshina Kannada, Udupi, Uttar Kannada, Mysore, Kodagu and Haveri with root knot index of 3, whereas, the Northern districts of Karnataka shows least root-knot index of 1, where the type of soil is black or vertisols. In all the rice growing districts, the organic content varied from <0.5 to >0.5. With regard to organic carbon content, no correlation was observed whether it was <0.5 or >0.5 as the same tendency of root-knot index and population levels were noticed in the districts where gall indices varied from 3 to 5 and population levels. Key Words : Rice, Meloidogyne graminicola, organic carbon. Current Nematology, 26(1,2) : 7–12, 2015 Rice (Oryza sativa L.) is one of the most impor- tant staple food crops of India. Projection of India rice production target for 2025 AD is 140 mt, which can be achieved only by increasing the rice production by over 2 mt per year in the coming decade and this has to be achieved against back drop of diminishing natu- ral resource such as land and water. The expected fu- ture demand for rice from increased population can no longer be met only by higher yields from irrigated areas, but also from rainfed situation (Ravindra et al., 2014) Rice is grown in Karnataka in different Agro- climatic zones with a rainfall pattern varying from 600 to 3000 mm Only around 44 per cent of the total acreage is under irrigation while the rest is under the regime of monsoon. In some areas, only one crop is grown and in certain other areas three crops are raised. The unique feature of rice culture in the state is that either sowing or transplanting is seen in all seasons of the year. The duration of the rice varieties cultivated in the state varies from 100 to 180 days depending on season and agro-climatic locations (Ravindra et al., 2014) Among the biotic stresses, rice root-knot nema- tode is a serious problem in the nurseries and upland rice but has been recently found to be widespread in the deepwater and irrigated rice also, in many states of India (Prasad et al., 1985). In India, the losses due to M. graminicola have been estimated to 16-32% and yield loss due to poorly filled kernels to 17-30% (MacGowan, 1989; Jain et al., 2007). The nematode occurs in patches within nursery