Histopathological And Transcriptomic Studyof The Early Interactions Between Peach Rootstock Roots And Meloidogyne Incognita

Root-knot nematodes(Meloidogyne spp.) are obligate, sedentary endoparasites of many plant species of the world. Their potential host range encompasses more than 3000 plant species. Meloidogyne spp. are responsible for huge economiclosses every year.Meloidogyne incognita is one of the most serious damage species. Root-knot nematodes are finding in all temperate and tropical region.Prunus kansuensis has wide adaptation and strong resistance, including ‘Bai Gen Gan Su Tao 1’which is highly resistance to M. incognita and‘Hong Gen Gan Su Tao 1’ is immune to M. incognita. ’Bailey’(P.persica) is highly susceptible to M. incognita. All of them are the elite peach germplasm to research the root-knot nematode resistance. The periods of root morphology changes induced by the early interaction between peach roots and M.incognita were precisely identifiedby comparing the changes in phenotype and tissue structures of the resistant ‘Bai Gen Gan Su Tao 1’ and susceptible ‘Bailey’in this study.This will provide basis for further resistance gene mining and resistance regulatory mechanisms research at the molecular level by transcriptomics. Based onperiod of root morphology changes identified above, seedlings of the immune ‘Hong Gen Gan Su Tao 1’ and the susceptible ‘Bailey’ were inoculated with M. incognita. Transcriptomic sequencing and analysis were conducted at each period which revealed a preliminary understanding of peach knot nematodes resistant and susceptible mechanism, and explanation resistance regulatory mechanisms. According to this study,the in-depth study of root-knot nematode resistance and marker assisted selection of peachwill be achieved in the future.The results are as follows:1. Established a in vitro rapid peach root-knot nematodes resistance identification method.Thismethod can identify root knot nematode resistance by countingthe amount of nematodes through dyeing after inoculation.It is less timeconsuming andcanbe inoculatedin a specific culture mediumindoor.2. The changes in root morphology after infection were precisely identified, and a preliminary description ofits resistance mechanismwas produced in this study. To study the changes in tissue structures and resistance mechanisms that occur due to the interaction between peach roots and root knot nematodes, seedlings of the resistant ‘Bai Gen Gan Su Tao 1’ and the susceptible ‘Bailey’ were inoculated with M. incognita using artificial indoor inoculation. Root tips were observed by staining at 6, 12, 18, 24, 30, 36, 42 and 48 h after inoculation, and the tissue structure of the root tips were observed by paraffin section at 0, 6, 12, 36, 60 and 84 h after inoculation. Staining results showed that the infection regular pattern of ‘Bai Gen Gan Su Tao 1’ and ‘Bailey’ were roughly similar: root knot nematodes invaded at 12 h after inoculation, and the number of root knot nematodes increased gradually during 12-30 h after inoculation. The number of root knot nematodes present in the roots subsequently decreased as the organisms began their upward movement along the plants’ vascular bundles. Compared with ‘Bailey’, at 30 h after inoculation ‘Bai Gen Gan Su Tao 1’ were infected with root knot nematodes at a significantly lower rate which only 28% of that of ‘Bailey’. Paraffin section results showed that the structural damage to inoculated ‘Bai Gen Gan Su Tao 1’ was much less severe than in inoculated‘Bailey’. Nematodes gathered in certain areas, which led to cells necrosis at the gathering sites at 84 h after inoculation.3. Resistance regulatory mechanismswere explained at the molecular level by transcriptome analysis. We identified 7081 differential expression genes through compared the transcriptome of the immune accession ‘Hong Gen Gan Su Tao 1’ and the susceptible accession ‘Bailey’ at 0,6,12,36,60 and 84 h after inoculation. 3380 genes were up-regulated and 3701 genes were down-regulated, respectively. The 12 h after inoculation may be a critical period because the number of differentially expressed genesbetween resistant and susceptible reached the maximum. A large number of genes involved in cellular processes, hormone synthesisand stress resistance were identified. Some genes had opposite or significant expression pattern between the resistant and susceptible accessions.These genes may play important roles in the formation of feeding sites, regulation of hormone and defense after inoculation.