Effect of elevated carbon dioxide on population growth of root-knot nematode, Meloidogyne incognita in tomato

Root-knot nematode, Meloidogyne incognita is a serious threat to the world vegetable production. However, our knowledge of M. incognita ’s response towards elevated CO 2 level is scarce. To investigate M. incognita population growth along with plant attributes at elevated CO 2 level, an experiment was conducted using tomato variety, Pusa ruby. Among the two sets of experimental design, one set of tomato seedlings were placed in ambient (385ppm) CO 2 chamber, whereas the other set in an elevated CO 2 (550ppm) chamber at National Phytotron Facility, ICAR-IARI, New Delhi. Two weeks later, the plants were inoculated with second stage infective juveniles of M. incognita population @ 0, 10, 100, 1000 and 10,000 nematodes per plant and maintained inside their respective CO 2 chambers for the next 45 days. At 45th day after nematode inoculation, the responses of M. Incognita on tomato plants were quantified for the plant parameters (growth variables). Results showed that the plant growth variables such as root length (f(1) = 65.06, p < 0.001), root weight (f(1) = 14.06, p < 0.001), shoot length (f(1) = 0.16, p < 0.691), shoot weight (f(1) = 5.146, p < 0.031) and total soluble sugars (f(1) = 4.74, p < 0.037), increased at elevated CO 2 compared to ambient CO 2 whereas, the nematode population growth variables such as the number of galls (f(1) = 19.53, p < 0.0001), number of females (f(1) = 11.48, p < 0.002), number of egg masses (f(1) = 7.99, p < 0.008) and multiplication rate (f(1) = 13.27, p < 0.001), and also soluble proteins (f(1) = 30.00, p < 0.0001) in roots decreased at elevated CO 2 than the ambient CO 2 level. Repetition of the same experiment with another variety SL 120 also follows the similar pattern and suggesting that the effect is independent of cultivar. Further, the sugars to protein ratio in the root system were found to be high (Pusa ruby-57.63%; SL 120-94.27%) at elevated CO 2 than the ambient. Thus, the cumulative response confirmed that the population growth of M. incognita gets significantly affected by increase in the atmospheric CO 2 level. The predicated sugar-protein ratio in root system at elevated CO 2 condition might demand adopting different nutrient cum nematode management strategies in future.