Root-Knot Nematodes Develop Resistance to Common Nematicides in Japan
In the complex world of agricultural science, farmers and researchers are engaged in a constant, invisible battle against microscopic enemies that threaten global food security.
Root-knot nematodes (Meloidogyne incognita) rank as one of the most destructive agricultural pests, causing an estimated $40 billion in annual crop losses worldwide 1 .
A 2024 study documents for the first time in Japan the emergence of root-knot nematode populations with dramatically reduced sensitivity to major nematicides 1 .
Understanding how these nematicides work and why resistance has developed is crucial for addressing this growing threat.
An organophosphate nematicide that targets the nervous system of nematodes by inhibiting the enzyme acetylcholinesterase (AChE) 1 5 .
This disruption prevents the proper breakdown of the neurotransmitter acetylcholine, leading to uncontrolled nerve signaling, paralysis, and eventually death.
OrganophosphateThe gene expression level of glutathione S-transferase (GST) was a staggering 239-fold higher in the resistant population 1 . This enzyme helps neutralize toxic compounds.
Soil samples containing M. incognita were collected from two distinct locations: Tahara City in Aichi Prefecture (no nematicide history) and Kamisu City in Ibaraki Prefecture (with a history of fosthiazate and 1,3-dichloropropene use) 1 .
The nematodes from each location were maintained on green pepper plants in a greenhouse to ensure a consistent supply for testing.
Second-stage juveniles (J2s) from both populations were exposed to varying concentrations of fosthiazate and fluopyram. The researchers recorded mortality rates at 24 hours post-treatment.
The team measured and compared the activity of AChE and GST enzymes in both populations using specific enzyme inhibitors.
DNA sequencing and gene expression analyses were conducted to identify differences in the AChE genes and GST expression levels.
Tahara City, Aichi Prefecture
No nematicide use for decades
Kamisu City, Ibaraki Prefecture
History of fosthiazate and 1,3-dichloropropene use
The experimental results revealed dramatic differences in how the two nematode populations responded to the nematicides.
The concentration required to kill 50% of the population (LC50) showed significant differences between sensitive and resistant populations.
| Nematicide | Aichi (Sensitive) LC50 (mg L⁻¹) | Ibaraki (Resistant) LC50 (mg L⁻¹) | Resistance Factor |
|---|---|---|---|
| Fosthiazate | 0.024 | 5.4 | 225-fold |
| Fluopyram | 0.011 | 2.3 | 209-fold |
Table caption: The Ibaraki population exhibited dramatically higher LC50 values for both nematicides, indicating significantly reduced sensitivity 1 .
The resistant population showed significantly enhanced enzyme activity and gene expression.
| Parameter | Aichi (Sensitive) | Ibaraki (Resistant) | Fold Difference |
|---|---|---|---|
| AChE Activity | Baseline | 33-fold higher | 33x |
| GST Expression | Baseline | 239-fold higher | 239x |
Table caption: The resistant population showed significantly enhanced enzyme activity and gene expression, explaining the resistance mechanism 1 .
The Ibaraki population had never been exposed to fluopyram directly, yet it showed reduced sensitivity to this chemically distinct compound 1 . This suggests that general detoxification mechanisms like GST overexpression may provide broad protection against multiple nematicides.
The discovery of nematode resistance to major nematicides carries significant implications for global agriculture and requires strategic responses.
This resistance likely developed due to continuous and exclusive use of the same chemical classes in the region. Between 2000 and 2014, fosthiazate was applied one to two times per year (15-30 total applications) in the Ibaraki fields, creating intense selection pressure 1 .
Implementing strict rotation schedules between nematicides with different modes of action will be essential to reduce selection pressure 4 .
Establishing regular monitoring programs to detect resistance early will help inform management decisions before failures occur in the field.
Investing in research to discover and develop nematicides with novel molecular targets will provide new tools where existing ones are failing.