The Studies On Citrus Root Rot Resistance Identification And Initial Gene Mapping Of Trifoliata Orange(Poncirus Trifoliata[L.] Raf) And Red Tangerine(Citrus Reticulata Blanco.) Hybrids

Citrus root rot(so called Phytophthora root rot)is an important soil-borne disease except Huanglong disease and Citrus canker disease in the citrus industry.Since the discovery of the last century,citrus root rot has spread to the major citrus-producing areas around the world.Pathogen infection usually causes root rot and cortex decay,has the potential to cause economically important crop losses.It is estimated that China has become one of the most largest country of citrus production which total cultivated area of 26,666km~2.Citrus root rot was founded in citrus nursery and orange groves and became a industry problem should not be ignored.Citrus cultivars are mostly susceptible to phytophthora root rot to some extent.There are no effective chemicals to control the disease at present.Therefore,it is important to breed disease resistant rootstocks and explain the molecular mechanism of citrus root rot.In this study,the susceptible material tangerine and resistant material trifoliata orange were used as parents for hybridization and the F1 hybrid population was obtained by embro rescue technique.The F1 generation disease resistance isolation was identified by inoculation.The multi-embryonic rate and germination rate of the seeds were evaluated.And the progenies with excellent resistance were screened by pathogen inoculation.The high-density linkage genetic map of SLAF was combined to genetically locate the root rot resistance of the hybrid population.The main findings are as follows:First,the in vitro inoculation experiments of root rot pathogens were carried out on the parents and the F1 generation of red orange×trifoliata orange hybrid population.According to the disease grading standards,38 of the 89 individual plants in the hybrid population were identified as susceptible plants,and 51 were susceptible plants.R:S=1.62:1(by the chi-square test).The results of in vitro leaf inoculation were verified by root inoculation test.Second,a QTL locus associated with the phenotype was found on the No.3 linkage group using a high-density linkage genetic map quantitative trait loci analysis,and the1.88M was locked on chromosome 3 with reference to the Kleinmann orange genome.Twenty-four candidate genes was selected as candidate gene relating to antibiotic and abiotic stress and verified by real-time PCR.Third,the phenological period,seed multiembryo rate and germination rate of red tangerine×trifoliata orange progenies were statisted in 2017.In the progenies,7 trees was selected with high germination rate,high root rot resistance and polyembryonic.This provides a alternative rootstocks material for further breeding new resistance citrus varieties.