The Chemical Constituents Form Flue-cured Tobacco Cultivar KRK26 Nematocidal Activity Against Meloidogyne Incognita

Tobacco root knot nematode disease is one of the most important diseases in tobacco production,which seriously restricts the development of tobacco economy.In recent years,with the continuous expansion of the scope of tobacco root knot nematode disease,there has been rampant abuse of pesticides,resulting in the enhancement of tobacco drug resistance,soil pollution,Tobacco yield quality and other problems.Therefore,with the demand of healthy ecology and sustainable development,green,safe and environmentally friendly plant pesticides for the control of root knot nematodes have become a new research hotspot,in which plant active molecules are the key substances,which is of great significance for the development of plant source pesticides.In this study,Meloidogyne incognita,the dominant root-knot nematode population in tobacco-growing areas of Yunnan Province,was selected as the target.Crude extract of KRK26,different solvent extracts and monomethyl compounds were selected as the screening objects.Laboratory Nematocidal activity tests,egg incubation tests and chemotaxis tests were carried out on Meloidogyne Incognita,the dominant root-knot nematode population in tobacco-growing areas of Yunnan Province.The monomeric compounds were isolated and purified,and the nematocidal activity was evaluated.In addition,pot experiments were conducted to verify the control effect of extracts on southern root-node nematode and the effect of extracts on the growth and development of tobacco（Nicotiana tabacum L.‘HD’）.（1）The extraction test showed that the active components of KRK26 were concentrated in the ethyl acetate extraction layer.When the concentration of KRK26 was 100.0mg/m L for 72h,the corrected death rate of C.elegans was 74.64%,LC₅₀ was 32.51mg/m L,and the inhibition rate of egg hatchability was 77%.At 2h,4h,6h and 12h,the nematodes were slightly attracted to the nematodes,and the chemotactic index decreased gradually after reaching the maximum at 6h.（2）Pot experiment showed that within a certain concentration range,KRK26 ethyl acetate extract had no significant effect on the growth and development of tobacco plants,chlorophyll and root activity,but with the increase of ethyl acetate extract concentration,the control effect was gradually enhanced.When the concentration was treated at T1,the control effect was 76.92%.（3）21 compounds were isolated and identified by modern chromatographic and spectroscopic techniques.For dibutyl phthalate（1）、butyl isobutyl phthalate（2）、met hyl 4-hydroxybenzoate（3）、bis（2-ethyloctyl）phthalate（4）、1,1′-oxybis（2,4-di-tert-butylbe nzene）（5）、2-O-butyl-1-O-（2’-ethylhexyl）benzene-1,8-dicarboxylate（6）、2,2’-oxybis（1,4）-di-tert-butylbenzene（7）、2-（3-hydroxy-4-methoxyphenyl）ethyl palmitate（8）、stigmas terol（9）、2-methyl-7,9-heptyl undecylate（10）、3,4,18β-cyclopropa-12β-hydroxy-ent-abi et-7-en-16,14-olide（11）、n-hexyl laurate（12）、1-octacosanol（13）、6-hept-2-enyl-5,6-dih ydropyran-2-one（14）、1-（4-Methoxyphenyl）-2-（naphthalen-2-yl）ethane-1,2-dione（15）、5β-acetoxy-1β,10α-epoxy-2-oxo-8β-tigloyloxygermacra-4（15）,11（13）-diene-12,6α-olide（16）、linalool（17）、stigmasterol stearate（18）、bis（2-ethylhexyl）benzene-1,2-dicarboxylat e（19）、（1S,2E,4R,6E,8S,11E）-2,6,11-cembratrien-4,8-diols（20）、N-phenethyl-2-formyl-5-hydroxymethylpyrrole（21）,21 compounds were isolated from this plant for the first t ime.（4）Compound activity screening test showed that,Three compounds were dibut yl phthalate（1）、2-O-butyl-1-O-（2’-ethylhexyl）benzene-1,8-dicarboxylate（6）、1-（4-Met hoxyphenyl）-2-（naphthalen-2-yl）ethane-1,2-dione（15）,strong nematocidal activity after72h when concentration was 100.0μg/m L,phenyl The corrected mortality rates wer e 52.22%,52.07%,61.18%,LC₅₀ were 84.07μg/m L,78.58μg/m L,69.01μg/m L,respe ctively.The five moderately active compounds are bis（2-ethyloctyl）phthalate（4）、2-（3-hydroxy-4-methoxyphenyl）ethyl palmitate（8）、stigmasterol（9）、5β-acetoxy-1β,10α-ep oxy-2-oxo-8β-tigloyloxygermacra-4（15）,11（13）-diene-12,6α-olide（16）、N-phenethyl-2-for myl-5-hydroxymethylpyrrole（21）showed moderate nematocidal activity at 100.0μg/m L after 72 h,with corrected mortality rates of 33.86%,44.36%,33.04%,46.84%an d 40.61%,respectively.LC₅₀ were 138.07μg/m L,105.19μg/m L,147.35μg/m L,104.99μg/m L and 130.19μg/m L,respectively.In summary,this study systematically studied the chemical composition of KRK26 and its effects on Meloidogyne incognita,screened out the ethyl acetate component with good activity and conducted pot experiments to verify its control effect and its effects on the growth and development of tobacco.At the same time,chemical components of the ethyl acetate component were separated and screened,and a screening system of plant-derived pesticides was established.To provide a theoretical basis for the development and utilization of KRK26 and other plant-derived pesticides.