Status of Meloidogyne graminicola under different organic carbon regimes of rice growing districts of Karnataka

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 districts, 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.