Effect of Root-Knot Nematode, Meloidogyne graminicola on the Uptake of Macronutrients and Arsenic and Plant Growth of Rice

Root-knot nematodes are known to induce morphological and physiological changes in tissues that affect the ability of the root to take up and transport water and mineral nutrients from the soil. Accumulation of toxic heavy metals in soil and possibility of their uptake by plants is also an emerging concern with increasing soil pollution. Investigations have been carried out on the effect of the root-knot nematode, Meloidogyne graminicola, a serious pest of rice, on the content of the major plant nutrients, viz., Nitrogen (N), Phosphorus (P) and Potassium (K) and the heavy metal, Arsenic (As) and growth of the basmati rice, Oryza sativa, cv. Pusa 1121. The content of NPK after 45 and 110 days of transplanting was significantly lower in the shoot of rice inoculated with 2 and 8 J2 cm(-2) soil compared to nematode-free plants, the reduction being more at the higher inoculum level. To the contrary, content of As in the plants grown in soil artificially contaminated with 5 and 10 ppm As was increased upto three times due to the nematode infection of roots, the increase being more at the higher inoculum level. The As content in plant was more at the higher soil contamination level. The plant growth in terms of height and dry weight was significantly (0.05P) decreased upto 50% and negatively correlated with the nematode inoculum level. In general, As contamination of soil upto 10 ppm did not cause significant reduction in plant growth or root galling due to M. graminicola but the trends indicated possibility of toxicity to both plant and nematode at higher As contamination levels. Similar effects were observed in artificially contaminated sandy-loam of Delhi and silty-clay loam of West Bengal. No As was detected in the shoot or grain of rice plants grown in untreated sandy loam soil of IARI farm, Delhi used in these experiments without or with M. graminicola inoculation. The results confirmed that M. graminicola infection of root can not only reduce uptake of NPK and decrease plant growth but it can also increase health hazard for humans and other consumers due to the increased uptake of the toxic heavy metal, Arsenic.