Preparation Of Three Types Of Chitooligosaccharide Derivatives And Preliminary Studies Of Their Lethal Activities Against Meloidogyne Incognita

Root knot nematode is an important kind of soil borne plant pathogenic nematode,which is widely distributed all over the world.Root knot nematodes have a quite broad host range,their second-stage juveniles?J2?could penetrate plant roots and get inside to form root knots,which would damage the function of root system,lead to the difficulties in the absorption of water and nutrients,and seriously affect the normal growth and development of plants.Root knot nematodes parasitize more than3000 species of plant,thereby causing yield losses rate of agricultural products is10%-30%annually,or even total crop failure in serious cases,which has become one of the most important threats to agricultural production in our country.Root knot nematode disease occurs underground and is easily transmitted through soil,water and plant residues,which is difficult to eradicate and easily forms complex infection with other bacteria,fungi and viruses,leading to great difficulties in treatment.There are limited varieties of nematocides and most of them have some disadvantages such as high toxicity,serious harm to non-target organisms and environments.Therefore,it is urgent to develop new environmentally friendly nematocides with high efficiency and low toxicity.China is rich in marine biological resources.There are many active substances from marine organisms with special functions that are not found in terrestrial organisms.The development of new green pesticides with marine active substances has a very broad application prospect.In this study,marine active substance chitooligosaccharide?COS?was used as a raw material,and different active groups were grafted onto COS backbones,respectively,through substructural splicing methods,thus,the aminourea chitooligosaccharide derivatives?AUCOS?,guanidinylated chitooligosaccharide derivatives and maleated chitooligosaccharide derivatives were designed and synthesized.The structures of these derivatives were characterized by infrared spectrum?FTIR?,¹H nuclear magnetic resonance?¹H NMR?,¹³C nuclear magnetic resonance(¹³C NMR)and elemental analysis.Meloidogyne incognita?M.incognita?was used to test the nematocidal activities of abovementioned COS derivatives in vitro.The main results are as follows:1.COS reacted with 1,2-dibromoethane and hydrazine hydrate successively to form the hydrazino-ethyl chitooligosaccharide?HECOS?,and then HECOS was used as the substrate to combine with three diamines by two ammonolysis reactions with dimethyl carbonate to prepare three AUCOSs.The results of nematocidal activities of the AUCOSs against the second-stage juveniles?J2?of M.incognita in vitro showed that the AUCOSs had higher nematicidal activities in vitro compared with chitooligosaccharide.The corrected lethality rate of the o-aminophenyl urea aminoethyl chitooligosaccharide derivative?AUCOS3?against the J2s was 27.13%at the concentration of 4 mg/mL,and its lethal concentration of 50%(LC₅₀)at 72 h was6.888 mg/mL,while the LC₅₀?72 h?of COS was 13.821 mg/mL.2.Methylated urea was prepared by the reaction of urea and dimethyl sulfate,and three guanidinylated COS derivatives were prepared by the reactions of methylated urea with COS and two kinds of multi-amino COS derivatives,respectively.The nematicidal activities of the guanidinylated COS derivatives against the J2s in vitro were also better in comparasion with the original chitooligosaccharide.Thecorrectedlethalityrateoftheguanidinylatedhydrazino-ethyl chitooligosaccharide derivatives?GHECOS?in 72 h at the concentration of 4 mg/mL against the second-stage juveniles was 58.34%,and its LC₅₀?72 h?was calculated as3.421 mg/mL.3.COS reacted directly with maleic anhydride to obtain the maleated products of chitooligosaccharide,and two kinds of multi-maleyl COS derivatives were further obtained after introduing more amino graft sites onto COS backbones and reacting with maleic anhydride.The results of nematicidal activities tests showed that the maleated COS derivatives showed significantly improvement compared with COS on nematocidal activities.The corrected lethality rate of the maleated polyaminoethyl chitooligosaccharide derivative?MPACOS?against the second-stage juveniles of M.incognita in 72 h at the concentration of 1 mg/mL reached 100%,its LC₅₀?72 h?was0.072 mg/mL,this value was significantly lower than the LC₅₀?72 h?of COS,and close to the positive control lythidathion's.In addition,the maleated COS derivatives also had strong inhibitory effects on the incubation of M.incognita eggs and the maleated polyaminoethyl chitooligosaccharide could completely inhibit the incubation of M.incognita eggs at the concentration of 0.2 mg/mL.In this paper,three new types of chitooligosaccharide derivatives were prepared through different grafting methods,and the obtained derivatives showed different degrees of improvement on lethal activities against M.incognita compared with COS,and the maleated COS derivatives had better utilization potentiality which had the highest nematocidal activities.The preparation of active nematocidal derivatives by modifying the raw COS not only broadens the application fields of COS,but also has certain reference significance for the development of new green nematocides.