| Quinoa(Chenopodium quinoa)is a traditional ancient grain-forage crop originated from Andes Mountains of South America,which is favored by people because of its rich and balanced nutrition and excellent resistance.In recent years,quinoa industry of China has developed vigorously.Quinoa downy mildew(DM),caused by pathogens Peronospora variabilis G?um.,is one of the most serious global diseases that damage quinoa.It often causes 33%～100% of the yield loss of quinoa and severely limits the production of quinoa.Therefore,it is of great significance to carry out the evaluation of quinoa germplasm resistance and research on its disease resistance mechanism to promote the control ability of quinoa DM and the healthy development of quinoa industry in China.This study systematically investigated the occurrence,damage and pathogenicity differentiation of quinoa DM in Gansu,and identified and determined the species of pathogens.Meanwhile,49 quinoa germplasms and 1 ‘Taiwan red quinoa’(Chenopodium formosanum)were identified and evaluated for resistance to DM in the local environment.Based on this,quinoa germplasms with different resistance to DM were selected as experimental materials,the effects of P.variabilis infection on leaf physiological indicators of resistant and susceptible quinoa materials were compared and analyzed,and the molecular mechanism of its response to P.variabilis infection was studied from the level of transcriptome and hormone metabolism.The disease resistance mechanism was explored from the physiological and biochemical,hormone metabolism and molecular levels,and the main results are as follows:(1)The systematic investigation showed that quinoa DM occurred severely in Gansu province,the disease broke out in some areas;the average incidence rate in different ecological areas of Gansu was 19.26%～83.7%,and the disease index was 16.67～80.44.The order of severity from high to low was: Linxia eryin climate area>Gannan alpine cold and wet area>Tianzhu alpine cold area>Lanzhou semi-arid area>Baiyin arid area.The degree of damage was closely related to the environmental humidity;the pathogen of DM in Gansu was identified as P.variabilis,and the size of sporangia and oospore in different ecological areas were significantly different(P<0.05);phylogenetic analysis showed that there were geographic genetic differentiation among DM strains in different ecological regions of Gansu;the pathogenicity of different strains was significantly different,and the order from large to small was:strain GSKL>strain GSLT>strain GSBY>strain GSLZ>strain GSTZ.(2)The resistance to DM of 49 quinoa germplasms and 1 ‘Taiwan red quinoa’ were evaluated and screened by the methods of field natural infection and indoor inoculation of the detached leaves.The results showed that there existed great variations in the infection degree of P.variabilis(Disease incidence 13.30%～100.00%;disease index1.00～100.00)and significant differences in the resistance degree of DM among quinoa germplasms.We respectively screened one highly resistant material ‘Taiwan red quinoa’,accounted for2.00% of the tested materials;one resistant material ‘QA064’,accounted for 2.00%;two moderately resistant materials ‘Long li No.2’ and ‘HL-Q5’,accounted for 4.00%;three susceptible materials ‘QA045’,‘QA050-2’and ‘Qinghai-02’,accounted for 6.00%;the remaining 43 materials showed highly susceptible,accounted for 86.00%.This study found for the first time that ‘Taiwan red quinoa’ could be infected by P.variabilis,and the resistance was evaluated as high resistance.(3)The activities of antioxidant enzymes(SOD,POD,CAT and APX),resistance related enzymes(PPO,PAL and β-1,3-glucanase)and the content of proline(Pro)in leaves of quinoa ‘QA064’(resistance)and ‘QH-01’(susceptibility)were determined after infection by P.variabilis.Results showed that the activities of leaf antioxidant enzymes,disease resistance related enzymes activity and Pro content increased in varying degrees after inoculation,and the overall changes were first increased and then decreased.The resistant cultivar ‘QA064’ could quickly improve the activities of its leaf antioxidant enzymes and disease resistance related enzymes to resist invasion.(4)The study on transcriptome of quinoa ‘QA064’ and ‘QH-01’ carried out after leaf inoculation by P.variabilis.3919 differentially expressed genes(DEGs)were identified in the resistant variety ‘QA064’,1800 and 2119 genes were up-regulated and down regulated,respectively;1660 DEGs were identified in the susceptible variety ‘QH-01’,826 and 833 genes were up-regulated and down regulated,respectively;there are 546 DEGs shared by two varieties,3373 of which are unique to ‘QA064’ and 1114 of which are unique to‘QH-01’.These genes are mainly involved in metabolic pathway,synthesis of secondary metabolite,plant pathogen interaction,plant hormone signal transduction,carbon metabolism,photosynthesis,phenylpropane biosynthesis,MAPK signal pathway plant and starch and sucrose metabolism pathway.Only the up-regulated DEGs in disease resistant variety ‘QA064’ were significantly enriched in phenylpropane biosynthesis and flavonoid biosynthesis pathways,and the genes encoding phenylalanine ammonia lyase(PAL),4-coumarinic acid Co A ligase(4CL),caffeioyl shikimate esterase(CSE),chalcone synthase(CHS)and other key enzymes were up-regulated,while in susceptible variety ‘QH-01’,they were down regulated or had no significant changes.It is speculated that these pathways play a key role in the disease resistance of quinoa ‘QA064’.In addition,the study found that2920 DEGs were annotated as transcription factors(TF),distributed in 92 transcription factor families,and a large number of TF were distributed in MYB,WRKY,b ZIP families related to disease resistance.These transcription factors may play a key and important role in disease resistance regulation.(5)Hormone metabolites of ‘QA064’ and ‘QH-01’ after inoculation by P.variabilis were studied by LC-MS/MS technology.The results showed that the content of 3 JA metabolites in the resistant variety ‘QA064’ after inoculation increased(2.64,6.12 and 6.11 times respectively)compared with the control treatment;the content of 9 hormone metabolites in the susceptible variety ‘QH-01’ after inoculation changed significantly compared with the control treatment,including 1 kind of ABA(0.32 times),5 kinds of JA(0.27、0.23、0.26 and 0.32 times respectively)and 1 kind of SL hormone(0.30 times)decreased significantly,while the contents of 1 kind of JA and 1 kind of SA hormone increased significantly(2.25 and 2.87 times respectively).The results showed that JA defense system of resistant cultivar ‘QA064’ was activated after DM infection,while multiple hormone signal transduction pathways were activated in susceptible cultivar‘QH-01’,especially SA hormone signal transduction pathways.KEGG enrichment analysis found that both of them were enriched in plant hormone signal transduction pathway,metabolic pathway,secondary metabolite biosynthesis and α-Linolenic acid metabolic pathway.Conjoint analysis found that P.variabilis infection were mainly involved in plant hormone signal transduction pathway and α-linolenic acid metabolic pathway.During the interaction between quinoa and P.variabilis,JAR1 and MYC2 related genes play a key regulatory role in JA synthesis and signal transduction,and transcription factors TGA and PR1 play an important role in SA synthesis and signal transduction.In summary,this study clarified the disease occurrence and harmfulness of quinoa DM in Gansu province,identified pathogen as p.variabilis,screened a amount of quinoa resistant germplasms.we clarified the resistant cultivar ‘QA064’ after inoculation by P.variabilis possessed good osmotic adjustment ability,high activity of related defense enzyme;the defense system was activated after DM infection by JA signal transduction;the quinoa resistance to DM was improved by phenylpropane biosynthesis and flavonoid biosynthesis pathways. |
PDF Full Text Request