Chemotaxis responses of Meloidogyne incognita towards tomato roots depends on concentration gradient of root exudates in vitro assay

Nematodes respond differently to various host-derived odorants which can be either an attractant or a repellent. However, nematodes require suitable concentration gradient of the host cues to respond. In the present study, we have systematically assessed the distance and optimum incubation time at which Meloidogyne incognita second stage juveniles (J₂s) respond to tomato root exudates and invasion via an in vitro assay using PF-127 medium. In vitro assay is highly suitable to investigate the nematode's host finding and invasion behaviour under stringent laboratory conditions. Tomato roots incubated for 2 hrs in pluoronic gel followed by exposure to M. incognita J₂s gave significant attraction with directional movement and penetration after 8 hrs as compared to the roots incubated for 0 hr, ½ hr, 1 hr and 1½ hrs. In addition, response of J₂s to host root signals was confirmed in terms of stylet movement or thrusting which was significantly increased by exposure to tomato root exudates and neurotransmitter resorcinol that is known to induce stylet thrusting along with accumulation of esophageal gland secretions. Similar stylet thrusting was not seen in water. Thus, the present study indicates that nematodes require proper gradient of host signals during the host recognition. These findings can be utilized for understanding the intricate plant nematode interactions which in turn beneficial for the development of novel nematode control strategies.