| Pinewood nematode(Bursaphelenchus xylophilus)is a worldwide quarantine pest,a pathogen of Pine Wilt Disease,which contributes significant economic losses to wood and wood products.At present,the prevention and control of the disease progress is slow,the key technical aspects is difficult to achieve substantial breakthroughs,and some of the traditional killing agent on human health and the environment poses a serious threat,so the development of a low-toxicity,highly effective nematicide is imminent..trans-2-Hexenal,also known as Algae aldehyde,is a C6 volatile compound.It widely present in nature,which mainly present in many vegetables,fruits.Furthermore,trans-2-hexenal has an extremely potent aroma and is therefore commonly used as an artificial flavoring and food additive.It is reported that trans-2-hexenal has a strong nematicidal activity against Meloidogyne incognita and Heterodera avenae,but the nematicidal mechanism of action is not clear.In this study,we have evaluated the effects of trans-2-hexenal on reproduction,growth and behaviour and efficacy against the pinewood nematode,Bursaphelenchus xylophilus.The results were as follows:1.trans-2-Hexenal fumigation of pinewood and effect on B.xylophilus At 25?,the P.thunbergii logs were fumigated with trans-2-hexenal(99% purity)in the concentrations of 139.8 g m-3,349.5 g m-3and 699 g m-3.The results showed that the mortality of B.xylophilus reached 100% from 63.6%.2.Effects of trans-2-hexenal on different developmental stages of B.xylophilus trans-2-Hexenal had significant nematicidal activity against L2 s,L3s and L4 s /adults of B.xylophilus,the L2 s was most sensitive and its LC50 value was 11.2 ?g m L-1.3.Effects of trans-2-hexenal on embryonic development of B.xylophilus The results showed that trans-2-hexenal seriously affected the embryonic development of B.xylophilus,which strongly inhibited the eggs hatching of B.xylophilus.The minimum cumulative hatching rate(20.0%)at a concentration of 200 ?g m L-1was observed at 12 h.4.Effects of trans-2-hexenal on reproductive ability of B.xylophilustrans-2-Hexenal inhibited the reproductive activity of B.xylophilus,mainly in reducing the number of nematode populations,inhibiting their reproduction rate and decreasing their egg deposition.Thetreatment groups of trans-2-hexenal(i.e.,36 and 55 mg m L-1)were 11×104 and 8.3×104,which were significantly lower than those in the solvent control group and the blank control group.The results of the reproduction of populations showed that the blank control group and solvent control group had higher populations of 7.6×103 and 7.25×103 compared to the treatment groups of trans-2-hexenal.Meanwhile,the reproduction rates that corresponded to the population sizes were evaluated: a high rate was observed in the blank control group(7.6× 103)and solvent control group(7.25 × 103),a medium rate(5.5 × 103)was detected in the treatment group at a dose of 36 ?g m L-1 and the lowest reproduction rate(4.15 × 103)was detected at a dose of 55 ?g m L-1.One female nematode laid fewer eggs(i.e.15 ± 0.5657 and15.5 ± 0.0707 eggs)after treatment with trans-2-hexenal at concentrations of 36 and 55 ?g m L-1 for 24 h and then with water for 84 h,and these numbers were significantly different compared with those of the solvent(19.4 ± 0.2828 eggs)and blank controls(21.3 ± 0.2357eggs).5.Effects of trans-2-hexenal on the length and on the proportions of females to males in two successive generations of B.xylophilus In the F1,the lengths of female nematodes(992.4 ± 0.605 ?m at 36 ?g m L-1 and 966.0 ±10.61 ?m at 55 ?g m L-1)in the treatment groups were significantly shorter than those of females in the solvent(1048.7 ± 0.257 ?m)and blank control groups(1085.7 ± 3.779 ?m).Additionally,the lengths of males treated with trans-2-hexenal at 55 ?g m L-1(849.1 ± 9.878?m)were significantly shorter than those of males treated with acetone solution(983.3 ±0.7464 ?m)and distilled water(1024.1 ± 2.0916 ?m).Notably,with consideration for further study,the lengths of nematodes in the third generation(F2)showed no significant difference between treatment and control groups.In both nematode generations assessed in this experiment,female nematodes were significantly longer than males.The proportions of females to males were also determined,and the treatments with trans-2-hexenal had no significant effects on the proportions in either the second or third generation.6.Effect of trans-2-hexenal on the the locomotion behaviour of B.xylophilus After exposure to trans-2-hexenal,the thrashing frequency of B.xylophilus decreased,the nematode showed abnormal distortion,mainly spiral curl or multiple curl.The results showedthat the nematodes treated with high concentration of trans-2-hexenal(100 and 80 ?g m L-1)showed abnormalities in the first 30 min,which were significantly different from those in the control group.After 30 min,surviving nematode behavior gradually returned to normal.7.Effect of trans-2-hexenal on the respiratory rate of B.xylophilus The effect of trans-2-hexenal on the respiration rate of B.xylophilus increased and then decreased.The results showed that the respiratory rates of nematodes in the treatment groups were higher than those of nematodes in the control groups before 5 h;the rates then declined gradually,and at 8 h the respiratory rates in the treatment groups were equal to that in the solvent control.At 10 h,the respiratory rates of nematodes treated with trans-2-hexenal at 36 and 55 ?g m L-1were significantly lower than that of the solvent control.In conclusion,trans-2-hexenal has strong nematicidal activity against B.xylophilus,providing a basis for elucidation of the mode of action of trans-2-hexenal against plant-parasitic nematodes in future studies. |
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