Evaluation Of Disease Resistance To Meloidogyne Enterolobii And Study On The Resistance Mechanism In Capsicum Pepper

In recent years,Meloidogyne enterolobii develops into the one of the major diseases of chili pepper in Hainan province.Cultivating resistant cultivars is the most efficient and economic method to control this disease.In our studies,42 Capsicum annuum and 53 Capsicum chinense were evaluated for the resistance to Meloidogyne enterolobii.The nematode development and physiological indexes between resistant and susceptible germplasms were detected,combined with transcriptome sequences analysis.The metabolic pathways and genes closely related to Meloidogyne enterolobii were identified to explore the mechanism of nematode resistance in chili pepper.It will lay a solid foundation for breeding nematode resistant varieties in the future.The main research results are as follows:1.Amone the 42 Capsicum annuum and 53 Capsicum chinense germplasms,eight were highly resistant(included two Capsicum annuum and six Capsicum chinense).32 germplasms were resistant(included six Capsicum annuum and 26 Capsicum chinense).37 germplasms were susceptible(included 18 Capsicum annuum and 19 Capsicum chinense).18 germplasms were highly susceptible(include 16 Capsicum annuum and two Capsicum chinense).2.The number of juveniles and nematode development speed in susceptible germplasms were much higher than in resistant ones.The second-stage juveniles were developed into third-stage after inoculation for seven days in susceptible germplasms and for ten days in resistant germplasms.Secondary infection was happened in susceptible germplasms within 30 days.Whereas in resistant germplasms,the juvenils could not developed into adult to lay eggs within 30 days.3.The activities of polyphenol oxidase(PPO),phenylalanine ammonia lyase(PAL),peroxidase(POD)and lignin content in Capsicum annuum and Capsicum chinense resistant and susceptible germplasms after inoculation at 0,3,6,9,12,15,20,25 and 30 days were measured.It was found that the PPO activity of the four pepper germplasms had similar trends.But the PPO activity of the resistant germplasms were higher than that of the susceptible germplasms,and the peaks in resistant germplasms appeared earlier.There was no significant difference in PAL activity between resistant and susceptible Capsicum annuum except for the peak value.The PAL activity of susceptible germplasms was generally higher than that of resistant pepper varieties in Capsicum chinense.The POD activity of the susceptible cultivars was higher than that of the resistant cultivars after inoculation in Capsicum annuum.The POD activity of the resistant cultivars were higher than that of the susceptible cultivars within 12 days after inoculation,and that of the susceptible cultivars was higher than that of the resistant cultivars after 12 days after inoculation in Capsicum chinense.The change of lignin content showed an increasing trend,and the increasing trend of the inoculation group was much higher than that of the control group,and the resistant germplasm was greater than the susceptible germplasm.These results indicated that the different physiological and biochemical indexes were changed by the infection of Meloidogyne enterolobii,and these indexes also affected the infection of Meloidogyne enterolobii.4.The transcriptome data of susceptible and resistance Capsicum chinense germplasms inoculated for 0,3,6,9 days were analysed.156.8 G high quality sequences were obtained with the Q20 above 97%,Q30 above 92%.80% of the sequences could aligned to the reference genome successfully.The Unigene sequences were aligned to the Pfam,GO,KEGG databases for annotation.77352 Unigenes were commented.The differentially expressed genes of each combination were screened by differential gene expression.GO functional enrichment analysis of DEGS indicated that transcription factor activity,hydrolase activity,oxidoreductase and other gene loci were associated with resistance to root-node nematode disease.Through the KEGG pathway enrichment analysis of DEGS,it was found that the main differentially expressed genes were enriched in phenylpropanol biosynthesis,plant hormone signal transduction,plant pathogen interaction,flavonoid biosynthesis and other metabolic pathways,and some gene loci with significant differences were screened out from the differentially expressed genes.