The Mechanism Constitutive Resistance Of 4 Camellia Species To Camellia Weevils(Curculio Chinensis)

Camellia spp.are important germplasm-resources for the development and utilization of economic forest crops in China.And they are mainly commended to planted for poverty alleviation in Southwest China.Domestic scholars have done a lot of work in the breeding and promotion of improed varieties of Camellia spp.for a long time.A series of high-yielding and high-quality varieties have been continuously selected and widely planted,which has broght considerable economic benefits to farmers.Recently,the pests represented by camellia weevil,Curculio chinensis Chevrolat occur frequently and seriously,and cause huge economic loss of Camellia spp.in some planting areas.The weak resistance to diseases and insects of some high-quality varieties has become an important obstacle to improve the economic benefits of C.spp.,especially C.oleifolia.The camellia weevil finishes its cryptic life cycle inside the camellia seeds and soil,which makes it is difficult to control C.chinensis with pesticides.It is an important path to improve the resistant abilty to camellia weevil,reduce the damage and ehance the stability of camellia industry with resistance breeding.It is an urgent research work to investigate the mechanism of C.spp.plants to C.chinensis,uncover the resistant traits and build the resistance model to evaluate the resistance of C.spp.to C.chinensis.In present study,according to the previous filed investigation,four important economic species C.chekiangoleosa,C.reticulate,C.sinensis and C.oleifera were selected as high-resistant,resistant,intermediate and susceptible hosts to camellia weevil,C.Chinensis for exploring the dominant factor infuluencing damage rate differently.Aim to find out the important physical resistance traits of C.spp.plants against C.Chinensis,the characteristics of adaptive evolution between C.Chinensis with hosts and the resistance to insect were analyzed.Meanwhile,based on the growth,development and intestinal microbial diversity of C.chinensis larvae,the chemical resistance characteristics(resistant active substances)of C.spp.plants to C.chinensis larvae were screened.Based on the screening of the constitutive resistance indexes of C.spp.plants against C.chinensis larvae,the resistance model were constructed with the concerned multiple resistance indexes.The results of the present study will provide a theoretical basis for revealing the resistance traits of C.spp.plants and screening of resistant varieties,and provide a new theoretical basis for resistance breeding of C.spp.plants in future.The main results are as follows:(1)The C.spp.plants had no significant effect on host adaptability differentiation of C.chinensis.Concerning the long-term coevolutionary relationship between C.spp.plants and C.chinensis in the main distribution regions in China,there was no obvious host adaptation due to host isolation.In this study,two mitochondrial genes(COI and ATP synthase)and one nuclear gene(EF1-?)were used to analyze the population diversity and population dynamics of C.chinensis.The diversity index of C.chinensis population in south China was low.The genetic differentiation index of geographical population was higher than that of plant host group.There was obvious haplotype sharing in each geographic population,haplotype diversity was low,and the isolated haplotype had nothing to do with host isolation.There was an obvious positive correlation between genetic distance and geographical distance between populations,and an obvious adaptive differentiation of high and low altitude was appeared under the pressure of terrain selection.The population dynamics analysis showed that the population of camellia weevil was unobviously in a stable expansion.(2)The constitutive resistance index,peel thickness of C.spp.plants obviously affected the damage rate of C.chinensis.According to the feeding preference experiments of C.chinensis adults to C.spp.plant species,there was no significant difference in the feeding preference of C.chinensis during the oviposition period.The thickness of the pericarp of the C.chekiangoleosa was larger significantly than the other three camellia species and the "snout" of the C.chinensis.The correlation analysis between the damage rate of four camellia species and the thickness of pericarp showed that the damage rate decreased exponentially with the increase of pericarp thickness.It indicated that pericarp thickness was a key constitutive resistance index affecting the damage rate of camellia weevil.(3)Chemical composition(content of tea saponin)of C.spp.plants significantly affected the isolated gut microbiota of C.chinensis and then affected the development of C.chinensis larvae.In the retrieval experiments,the development of C.chinensis larvae reared by different Camellia plants was obviously inconsistent.The analysis of the gut microbiota of the re-covllected mature larvae showed that the gut microbiota was obviously shaped by the host plants,and the flora structure was significantly different.The diversity index and relative abundance were significantly different.There were also significant differences in the dominant flora of the gut microbiota of the three host-derived larvae,and the gut microbiota of the three host-derived larvae had unique flora.Serratia,Erwinia,Pantoea and Serratia occupied a high proportion in the intestinal microbiota of larvae received from C.oleifera.Lactobacillus,Serratia and Rickettsia were predominant in the intestinal microbiota of larvae received from C.sinensis.However,Acinetobacter,Bacteroides and Blautia in the gut microbiota of larvae received from C.reticulate with high content of tea saponin occupied higher weight,and Serratia,Erwinia,Pantoea,Lactobacillus and Rickettsia are less.The results indicated that there were key secondary substances in the fruits of host plants that affected the gut microbiota of camellia weevil,and then affected the development of C.chinensis larvae through influencing the beneficial flora of camellia weevel larvae participating in nutrient metabolism.(4)Five compounds,including caffeine,tannic acid,catechin,tea saponin and theanine,had significantly different effects on the structure of gut microbiota in vitro culture,and tea saponin was the main factor affecting the structure of gut microbiota in vitro culture.In this study,five plant resistant components that have been widely reported to have toxic and injurious effects were selected for in vitro culture of gut microbiota.Four alpha diversity index test,the random forest microorganism abundance test and the similarity analysis between groups in the tea saponin treatment group were significantly different from other treatment groups,and tea saponin concentration was negatively correlated with the diversity of bacteria.The accumulation of tea saponin was negatively correlated with the development of larvae.In this study,the abundance of Micrococcus,Bacillus,Lactococcus and Cupriavidus increased with the increase of tea saponin concentration,and the abundance of six bacteria genera(Erwinia,Serratia,Enterobacter,Proteus,Citrobacter)decreased.It was found that the increase of tea saponin concentration significantly up-regulated exogenous biodegradation metabolism,nucleotide metabolism,terpene and polyketone metabolism.Many other pathways were inhibited including amino acid metabolism,lipid metabolism,carbohydrate metabolism,biosynthesis of other secondary metabolites,amino acid metabolism,cofactors and vitamins,and biosynthesis and metabolism of sugars.Tea saponin was the main chemical resistant component of C.spp.plants that affected the development of C.chinensis larvae.(5)The contribution of pericarp thickness and tea saponin concentration to the resistance evaluation model was dominant.In the present study,a multivariate linear regression model of C.oleifera against C.chinensis was constructed based on the samples of C.oleracea with the highest economic benefits to obtain the component resistance indexes of C.oleifera.Based on the determination of constitutive resistance traits of common C.oleracea clones,the relationship between resistance indexes of C.oleifera and damage rate of C.chinensis was firstly comprehensively analyzed by using multiple linear regression model in four critical harm periods,and the evaluation model of C.oleifera resistance to C.chinensis was initially constructed.The thickness of C.oleifera and the concentration of tea saponin in the development stage of camellia weevil larvae played key roles in the model,and the contribution of fruit shape index in the model was not significant.This model could provide evaluation basis for the resistance of new C.oleifera varieties to C.chinensis,and provide new ideas for the breeding of resistant oil tea varieties to insect pests in China.