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A soil-less system for culturing rice root-knot nematode, Meloidogyne graminicola

Kumar, Puneet, Kumar, Vinod, Mohan, Sharad, Walia, Raman Kumar
Meloidogyne graminicola, Oryza sativa, climatic factors, edaphic factors, eggs, germination, greenhouses, juveniles, nutrient solutions, rice, root galls, root systems, root-knot nematodes, roots, seedlings, seeds, shoots, sodium hypochlorite, soil, submergence, tap water, temperature, trays, India
The rice root-knot nematode, Meloidogyne graminicola Golden & Birchfield, 1965, is a serious pest of rice throughout the world. Rice nurseries in particular are severely damaged under varied climatic conditions in India (Anonymous, 2016). Meloidogyne graminicola is reported to cause 17-30% yield loss due to poorly filled kernels (MacGowan & Langdon, 1989). Maintaining cultures of M. graminicola in glasshouses in potted rice plants out of season is usually difficult. Therefore, we developed a laboratory/growth room technique based on a soil-less system that ensures continuous availability of large amounts of M. graminicola culture for experimental purposes. It is hypothesised that tight entanglement of roots in a net should support nematode root invasion in the absence of its natural soil environment. The technique involves raising rice seedlings in plastic trays (length, width, height: 28 × 23 × 9 cm). Rice seeds (‘Pusa Basmati 1121’, susceptible to M. graminicola) were soaked in tap water overnight, transferred to a wet cloth bag and kept in a BOD incubator at 35°C for 2 days. The sprouted seeds were placed evenly at 125 g per tray directly without any soil or other medium, and kept wet by minimum submergence in water to continue germination (Fig. 1A). The trays were stacked in a growth room at 30-32°C (National Phytotron Facility, Indian Agricultural Research Institute, New Delhi). Upon germination, the roots gradually developed into a network forming a carpet of about 1 cm thickness (Fig. 1B, C). Approximately 25 000 second-stage juveniles (J2) of M. graminicola in 50 ml of water suspension were poured uniformly in the tray by lifting the rice seedling mat and placing it back after releasing the nematode suspension. The trays were maintained at 30-32°C and roots kept wet by applying 100 ml water daily. In the first 15 days no nutrient application was required; however, Hoagland’s nutrient solution was applied subsequently until the completion of the life cycle (25 days). Root invasion by J2 took place normally and root galls were visible within 2-3 days. The galls could be viewed through the transparent base of the plastic trays (Fig. 1D). Nematode development proceeded normally. By providing a near optimum temperature, the nematode completed its life cycle and egg-bearing galls could be obtained 25 days after nematode inoculation. After 30 days the entire carpet of the seedlings was removed from the trays. The root carpet was separated by culling the shoots. Additional eggs were obtained from the root system by macerating the roots in a blender with sodium hypochlorite as described by Hussey & Barker (1973).