Surveys of major rice growing districts in the state of Uttar Pradesh in Northern India were conducted for 3 consecutive years during 2013 to 2015 under a government-funded major research project to determine the frequency of occurrence and disease incidence of the rice root-knot nematode, Meloidogyne graminicola, in rice paddy fields. More than 800 paddy fields from 88 Tehsils (divisions within a district) in 18 major rice growing districts in Uttar Pradesh were surveyed, where M. graminicola was associated with root-knot disease in rice paddy fields based on morphological and molecular characterization of juveniles and adults. The highest frequency of disease in rice fields was observed in Aligarh (44.6%), followed by Muzaffarnagar, Shahjahanpur, and Kheri Lakhimpur (29.3, 28.0, and 27.4%, respectively). Maximum disease incidence was also recorded in Aligarh (44.6%), followed by Sultanpur, Mainpuri, and Muzaffarnagar (5.7, 5.2, and 4.5, respectively). Gall index and egg mass index values (on a 0 to 10 scale) were highest in Aligarh (3.5 and 2.1, respectively), followed by Muzaffarnagar (2.6 and 2.0) and Mainpuri (2.3 and 1.8). The average soil population of M. graminicola was highest in Aligarh (3,851 ± 297 second-stage juveniles [J2]/kg of soil), followed by Muzaffarnagar (2,855 ± 602 J2/kg of soil), whereas the lowest population was recorded in Barabanki (695 ± 400 J2/kg of soil) at the time of harvesting. Relative yield losses were also determined, and the highest yield loss attributed to M. graminicola infestation was recorded in Aligarh (47%). The yield loss was linearly correlated with the soil population density of M. graminicola and disease incidence.

The potential effect of rhizobial inoculation on root knot nematodes in chickpea, mungbean and pigeonpea were studied under field condition. The seed treatment with respective rhizobium strains increased the nodulation, leghemoglobin content, bacteriod population, plant growth, yield and nitrogen uptake of three three food legumes compared to the plants without the rhizobium treatment. The nematode (1500 juveniles/kg soil) incited oval galls on the roots of the three legumes, and suppressed plant growth and yield. The galling, egg mass production and soil population of the nematode was greater on the plants without the rhizobium treatment. The pure culture and culture filtrate of the rhizobium strains suppressed the egg hatching and induced mortality to the juveniles of M. incognita over control. The nematode infection reduced the nodulation, bacteroid population and leghemoglobin contents of the nodules and NPK uptake by the plants. Hence, the rhizobia treatment shall be integrated to common agronomic practice of food legume cultivation so as to enhance crop productivity and to protect roots from nematode attack.