Screening Of Accession Resistant To Pear Valsa Canker And Studying Of Their Physiological Characters In Pyrus Germplasm Resources

Pears are the third fruit in China. Its area and yield follows behind apples and oranges. The yield of pears in China is the largest in the world. Valsa canker of pear, caused by Valsa mali var. pyri, is one of the major diseases of pear tree. The pathogen main infect the pear tree trunks, main branchs and lateral branchs, making the pear trees weak and branches dead, severely reducing the pear output and quality, causing serious economic loss to pear industry.This research wants to find out which kinds of Pyrus germplasm accessions can resist to Valsa canker of pear, establishing pear anti-Valsa canker’s evaluation system.46 Pyrus germplasm accessions were inoculated with the fungal block (Valsa mali var. pyri) on the excised twigs for two years, and the relative POD, SOD activity, total phenolic content and tissue looseness were measured. The content of SA and JA were determined by using ELISA. According to SA and JA synthesis related genes (PAL, ICS, AOS and AOC) fragment sequence, which were obtained from RNA-Seq, the relative expression levels were analyzed by real-time quantitative PCR (qRT-PCR) technology.And the results are as followed:(1) Differences in disease incidence and severity were found among Pyrus germplasm accessions. Among, the results showed that 12 Pyrus germplasm accessions are canker-resistant, and 12 Pyrus germplasm accessions are canker-susceptive. In general, P. ussuriensis Maxim, type resources are strong canker-resistant, following with P. bretschneideri Rehd., P. pyrifolia Nakai. and P. sinkiangensis Yu. P. communis L type resources are canker-susceptive.(2) There was no significant correlation between POD and SOD activity, epidermal thickness and epidermis layer with Valsa canker disease degree; related positive correlation between total phenolic content in phloem of twigs with Valsa canker disease degree.(3) In canker-resistant germplasm P.breschneideri Redh. cv. Qiubai, the endogenous SA and JA levels were increased after applied with V. mali var. pyri. The expression level of AOS and PAL also increased under the treatment of the pathogen. However, the content of SA and JA levels were no significant changed to the pathogen in ’Chili’, which is canker-susceptive P.breschneideri Redh. Consistent results were found in the expression of PAL, AOS, AOC and ICS genes. Analysis showed that SA and JA participate in the response of pear to the pathogen of V. mali var. pyri.