Submitted to: Journal of Helminthology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 4, 2007
Publication Date: June 1, 2007
Citation: Masler, E.P. 2007. Responses of Heterodera glycines and Meloidogyne incognita to exogenously applied neuromodulators. Journal of Helminthology. 81:421-427.
Interpretive Summary: Plant-parasitic nematodes attack all crops of agricultural importance, causing over $10 billion in losses annually to U.S. farmers. One problem facing growers is that environmental concerns will result in the elimination of the most extensively used chemical nematicide from the United States within the next few years. This loss makes the discovery of environmentally and economically sound replacement control agents critical. One approach to discovering new ways to control nematodes is to identify ways to disrupt their normal biochemical processes by using chemicals that occur naturally inside the nematode. We have discovered that a group of small molecules called biogenic amines, which are produced naturally by nematodes, can be used to control movement and hatching in plant-parasitic nematodes. The discovery is significant because it identifies targets in plant parasites which can be used to control the nematodes. Consequently, this information will be used by researchers in the agrochemical and agricultural biotechnology industries who are developing safe, selective methods for nematode control.
The biogenic amines dopamine, octopamine and serotonin each have significant but differing effects on behavior in juveniles of the plant-parasitic nematodes Heterodera glycines and Meloidogyne incognita. Body movement frequency was increased 2-fold in H. glycines by 5mM dopamine (P = 0.00013), while 50mM dopamine resulted in frequency decreases in both H. glycines (88%) and M. incognita (53%) (P < 0.0001). 50mM octopamine increased frequencies in both species by 50-70% (P < 0.0001) while 5mM increased M. incognita frequencies more than 2-fold (P < 0.0001). Also, the invertebrate neuropeptide FLRFamide increased M. incognita body movement frequency by 45% (P = 0.02). 5mM serotonin inhibited body movement by more than 90% in both species (P < 0.0001), and was inhibitory to as low as 0.5mM. Amplitude of body movement in H. glycines was unaffected by any of the amines, whereas amplitude in M. incognita was significantly reduced by all three (P < 0.0006). The frequency of stylet pulsing was not affected by dopamine or octopamine in either H. glycines or M. incognita, but 5mM serotonin stimulated pulsing in H. glycines by nearly 13-fold (P < 0.0001) and in M. incognita by more than 14-fold (P < 0.0001). Egg hatch in H. glycines was completely suppressed by 50mM serotonin, and partially suppressed by 50mM doses of dopamine (75% suppression; P < 0.0001) and octopamine (55%; P < 0.0001). Neither dopamine or octopamine affected hatch at 5mM, but serotonin remained suppressive through 0.5mM (16%; P = 0.0018).