Plant Immunity Inducers Induced Rice Resistance To Rice Seedling Blight And Its Mechanism

Rice seedling blight is a soil-borne disease mainly caused by fungi such as Fusarium oxysporum,and it is also the main disease of dry rice seedlings.After the onset of disease,the root of rice seedling will rot,resulting in obstruction of nutrient absorption and yellowing of the heart leaves,causing the seedlings to dry up and die,bringing g reat harm to rice production.At present,fungicide is mainly used to control rice seedling blight in production,but there are many problems such as short duration of drug effect,easy to develop drug resistance and environmental pollution.Another important way of plant diseases control is to induce plant disease resistance by plant immune inducers.It has been widely used in the prevention and control of plant diseases in recent years due to its many advantages such as long duration,broad-spectrum effect,no drug resistance,low concentration,no harm to human body,and no pollution to the environment.It has become a hot topic in plant disease control research.However,systematic studies on the use of inducers to control rice seedling blight have been seldom reported,and the physiological and molecular mechanisms of inducing resistance to rice seedling blight are still unknown.Therefore,a comprehensive and systematic study on rice resistance to seedling blight induced by immune inducers can provide technical support and theoretical basis for the large-scale application of immune inducers to control rice seedling blight and enriching the physiological and molecular basis of resistance to rice seedling blight.It is of great significance to establ ish the technical system of green control and pesticide reduction of rice disease.In this study,364 rice varieties were evaluated for resistance to rice seedling blight,and 6 varieties with different resistance types were selected to determine the patho genicity differentiation of 129 F.oxysporum strains which were collected and isolated in Heilongjiang Province.The disease resistance types of 364 varieties and the pathogenicity differences among F.oxysporum strains were identified in our study.The high-sensitivity seedling blight variety Qijing 2 and the highly pathogenic strain QA09 were used as experimental materials,the three-factor orthogonal design was adopted to optimize the induction scheme and evaluates the induction control effect of 12 kinds of inducers on rice seedling blight.The effects of fluoro-substituted benzothiadiazole derivatives(FBT)and chitosan oligosaccharide(COS)on dry matter accumulation,root morphology,membrane permeability,key enzyme activity of antioxidant system and d efense system in rice seedlings under F.oxysporum stress were analyzed.The induced resistance to rice seedling blight were elucidated from morphological and physiological perspectives.Transcriptome and proteomic analyses were used to reveal the possible molecular mechanisms of inducing disease resistance at the transcriptional and translational levels respectively.The main research results were as follows:(1)There were significant differences in the resistance of the tested varieties to rice seedling blight(P<0.05),and the two-year disease index was between 4.2?78.8 and 5.6?81.3 respectively.Among the 364 tested varieties,there were 220 varieties with the same type of disease resistance in 2 years,among which only 7 varieties were high resistant varieties,26 varieties were moderate resistant varieties,59 varieties were moderate susceptible varieties,and there are 101 susceptible varieties and 27 high susceptible varieties.The high and moderate resistant varieties accounted for 9.06%,while the susceptible and high susceptible varieties 35.17%,indicating that the susceptible varieties were significantly more than the resistant varieties.(2)A total of 312 seedling blight strains were isolated from disease samples collected from 13 rice producing areas in Heilongjiang Province.According to the morphological characteristics of F.oxysporum and EF-1? gene sequence analysis,a total of 129 F.oxysporum strains were isolated and identified.The pathogenicity of F.oxysporum strains was determined by selecting 6 varieties of high-resistance,medium-sensitivity and high-sensitivity varieties.The results showed that there were significant differences in pathogenicity between the strains(P<0.05),and the difference of disease index ranged from 13.4 to 43.1.Cluster analysis was used to divide 129 strains into 4 pathogenic type groups,among which type ? F.oxysporum group was a strong pathogenic type group with an average disease index of 41.5,accounting for 9.3% of the total strains.Type ? F.oxysporum group was a pathogenic type group with an average disease index of 33.5,accounting for 28.7% of the total strains.Type ? F.oxysporum group was a weak pathogenic type group,with an average disease index of 17.8,accounting for 27.9% of the total str ains.Type ? F.oxysporum group was a medium pathogenic type group with an average disease index of 25.3,accounting for 34.1% of the total strains,which was the group with the largest number of strains.(3)There was no significant bactericidal effect of 12 inducers on F.oxysporum at different concentrations.The induction scheme was optimized by orthogonal experiment of three factors: different induction concentration,induction frequency and induction mode.Under this scheme,there was a significant difference in the control effect of 12 inducers against rice seedling blight(P<0.05),FBT and COS had the highest control effect(82.2% and 80.3%),which was significantly higher than the other 10 inducers.(4)After inoculation with F.oxysporum,rice plants without FBT and COS treatment showed obvious inhibition of seedling root growth,slow growth of overground and root dry matter,and decreased root-shoot ratio.For rice seedlings,FBT and COS alleviated the inhibition of root growth,significantly increased root length,root surface area and root volume,and promoted the accumulation of dry matter in overground and root.At the same time,the root-shoot ratio was improved,and the accumulation and distribution of matter in overground and underground parts were balanced to promote the healthy growth of seedlings.(5)FBT and COS treatments significantly reduced MDA content and relative conductivity of seedling roots under F.oxysporum stress,and alleviated the damage of cell membrane.FBT and COS treatments could significantly improve the activity of POD,SOD,CAT,PPO and PAL in seedling roots under F.oxysporum stress,enhance the antioxidant ability and defense ability of rice roots,and improve the resistance of rice to seedling blight.(6)Transcriptome analysis showed that 6,988 differentially expressed rice genes were induced by FBT and 6,599 differentially expressed rice genes were induced by COS.KEGG pathway enrichment analysis showed that the differential genes treated by FBT and COS participated in 125 and 122 pathways,respectively.Real-time quantitative PCR verification results showed that transcriptome sequencing data were true and reliable.In this study,it was found that a number of pathways with the same function of FBT and COS were involved in inducing resistance to rice seedling blight resistance.Both FBT and COS treatments could improve the expression of multiple PR-1 genes in the salicylic acid(SA)pathway,activate the SA signal transduction pathway,induce the production of system acquire resistance(SAR)in rice to resist the infection of F.oxysporum.The AUX1,SAUR,GH3 and BRI1 genes were up-regulated in FBT and COS treatment groups,so as to activate auxins and brassinolide(BR)signal transduction pathway to play the role of disease resistance.In addition,both FBT and COS treatments could increase the expression level of genes encoding CYP86A4,fatty acid omega-hydroxy dehydrogenase and alcohol-forming fatty acyl-Co A reductase,thereby promoting the biosynthesis of cutin,suberine and wax to enhance the resistance of rice to seedling blight.(7)Proteomic analysis showed that 922 differentially expressed proteins were identified by FBT treatment,among which 150 differentially expressed proteins were enriched into 9 KEGG pathways.And 1323 differentially expressed proteins were identified by C OS treatment,among which 187 differentially expressed proteins were enriched into 14 KEGG pathways.The real-time quantitative PCR verification results showed that the proteome sequencing data were true and reliable.In this study,it was found that a number of proteins common to FBT and COS were involved in inducing resistance to rice seedling blight.In the FBT and COS treatment groups,two ent-copalyl diphosphate(CPSent)synthase(Os CPS1 ent and Os CPS2ent)were significantly up-regulated,which promoted synthesis of ent-copalyl diphosphate in rice to synthesize plant antibiotics against F.oxysporum infection.At the same time,both FBT and COS could improve the expression level of momilactone synthase,promote the biosynthesis of momilactone,and enhanc e the resistance of rice to seedling blight by accumulating a large amount of momilactone.