Screening Of Rootstock Resources Resistant To Foot Rot Of Citrus&Fungicides And Prediction For RXLR Effectors From Phytophthora Parasitica

Foot rot of Citrus, also known as foot rot and rotten stump scar, is a kind of disease that via ground to spread and harms the bottom of citrus stem and has occurred in all citrus production areas of China. The primeval symptom of foot rot is that the rind appears anomalous appearance of wet and rot, then brown and always outflow brown liquid with smell of draff. When the disease extends to the xylem, it will discolor and decay the xylem and the border of disease and health tissue becomes clear. In the later stage, the rind will dry and exfoliate and the xylem becomes exposed. The majority of studies argue that foot rot is caused by the Phytophthora, such as Phytophthora parasitic, Phytophthora citrophthora, Phytophthora capsici and so on, While, a few studies believe it is caused by Fusarium. The most economical and effective measures of preventing foot rot are to choose resistant rootstock, such as Poncirus trifoliata, Citrus junos, Citrus limonia Osbeck and Goutou cheng, which always be the rootstocks in production. The common methods to prevent foot rot include inarching and changing rootstock, selecting disease-resistant resources for stocks, enhancing the field management of cultivation and drug prevention and control, etc.In the screening test of resistant rootstock, separated pathogens of foot rot at first.Separated pathogens of foot rot according to the normal tissue separation method, and extracted pathogen DNA by the way of CTAB extraction, using the universal primers ITS1and ITS4of ribosomal DNA. Then compared the sequencing homology on NCBI sites after sequencing amplification products. According to the comparison results, the kind of pathogenic bacteria was determined and isolated. We inoculated Phytophthora parasitic’s hypha on the uncompleted mature leaves and screened the103kinds of citrus resources that could be used as rootstock. After7days, judging by the square of diameter size of the disease spot of leaves infected with pathogen, the rootstock resources were divided into six classes, such as high resistance(HR), resistance(R), medium resistance(MR), medium susceptible(MS), susceptible(S), high susceptible(HS). The result indicated that, Luohan cheng, Early flowing trifoliate orange, Citrus limonia Osbeck, Citrus junos Sied.ex Tanaka were HR resources, in addition to the traditional resistant rootstock resources such as Poncirus trifoliate Raf, Citrange, Citrus aurantium L.; Gulaoqian Shatian pummelo, Wanbai pummelo, Wubuhongxin pummelo were identified as S resources, and the same to most of Citrus limon, Citrus bergamia Risso, Citrus sinensis, Cirtrus Medica.In the chemical control test, the way of hypha growth rate was adopted to conduct indoor toxicity screening of21kinds of fungicides for Phytophthora parasitica. It was found that every medicament under different concentration gradient restrained the growth of Phytophthora parasitica hypha, and the rate was positive correlated with medicament concentration. Using DPS software for statistical processing of data, we got the virulence regression equation, medium inhibition concentration (EC50) and correlation coefficient (R) of every medicament to Phytophthora parasitica, and the data showed that Dimethomorph was the best, the next was Pyraclostrobin-metiram, Kasumin, Iprovalicarb and Polyoxins. These agents can be tried to prevent and treat foot rot in production.Using bioinformatics analysis in the experiment, we found that there were about248candidate effect molecules, containing signal peptide and having RXLR-dEER conservative function domain on the downstream. Prediction for RXLR Effectors laid the foundation for research of interaction between avirulence genes and resistance gene.