Abstract
The
in vitro inhibition potency of some organophosphates (OPs) and carbamates (CAs) which are widely used to control plant-parasitic nematodes on acetylcholinesterase (AChE) of
Meloidogyne javanica,
Heterodera avenae and
Tylenchulus semipenetrans, the major pathogens responsible for the damage of a wide range of crops in Al-Qassim region, Saudi Arabia was examined. AChE of
H. avenae activity was 1.58- and 1.51-fold greater than that of
T. semipenetrans or
M. javanica, respectively. The order of inhibition potency of the tested compounds against
T. semipenetrans AChE was: carbofuran
>
paraoxon
>
oxamyl
>
fenamiphos
>
phorate-sulfoxide
>
aldicarb, where the corresponding concentrations that inhibited 50% of the nematode AChE activity (I
50) were 5
×
10
−8, 7
×
10
−7, 7.5
×
10
−7, 2
×
10
−6, 2
×
10
−4 and 2
×
10
−3
M, respectively. Paraoxon, fenamiphos and carbofuran exhibited high inhibition potency against
M. javanica AChE where the I
50 values were below 1
nM. Phorate-sulfoxide and aldicarb were potent inhibitors of
M. javanica AChE with I
50 values of 3.8 and 8
nM, respectively, while oxamyl exhibited low inhibition potency with I
50 of 15
nM. Fenamiphos and paraoxon showed the highest I
50 values of <100
μM
against H. avenae followed by oxamyl (I
50
<
1
mM), whereas paraoxon, carbofuran and aldicarb showed low potency with I
50 values >1
mM. All the tested compounds exhibited high inhibition potency to AChE of
M. javanica than
T. semipenetrans or
H. avenae. Except phorate-sulfoxide in
M. javanica the inhibition pattern and implied mechanism for all the tested compounds for the three nematodes is suggested to be a linear mixed type (a combination of competitive and non-completive type).