Title : High diluted solution of Thuya occidentalis changes photosynthetic response curves in tomato plants infected with Meloidogyne incognita
Abstract:
The use of high dilutions on plants may cause changes in plant metabolism and result in disease control by inducing resistance. This work aimed to study the physiological responses of tomato plants (Solanum lycopersicum L.) infected with the root-knot nematode Meloidogyne incognita and treated with highly diluted preparations of Thuya occidentalis. The treatments included: T. occidentalis 6CH, 24CH, and 50CH (CH: centesimal Hahnemanian) prepared according Pharmacopoeia; a water control (with nematode and without treatment); and an absolute control (no treatment and no nematode). At the time of transplanting, the root system of the tomato seedlings was dipped in 0.1% of treatment solution (1 mL of solution diluted in 1 L of distilled water) before seedlings were planted in the pots. Seven days after planting, seedlings were inoculated with pathogen. Gas exchange was measured on full sun days, between 9:00 am and 11:00 am, using an infrared gas analyzer (IRGA) portable photosynthetic system (Li-6400XT, LI-COR, Lincoln, Nebraska, USA). Gas exchange measurements were done prior to nematode inoculation and five, eight, and 13 days after inoculation. Measurements were performed in 6 cm² of the second fully expanded leaf that was exposed to sunlight. Photosynthetic rate, stomatal conductance, transpiration, leaf internal CO2 concentration, and leaf temperature were measured at various photosynthetic photon flux densities, varying from 1800 µmol m-2 s-1 to zero and measurements started at 400 µmol mol-1 of CO2. Experiments were conducted in a greenhouse using a randomized block design with four replications. No significant difference was found in the different gas exchange specific measure parameters between the treatments. Untreated infected plants showed an increase in net photosynthesis and in the carboxylation capacity, as shown by the light response curve. Treatment with T. occidentalis 24CH inhibited the increase in CO2 fixation in tomato plants inoculated with the pathogen M. incognita, leading to a similar behavior as healthy plants, independently of the photon density
