| Valsa canker is an important stem disease of pear. The disease frequently retarded trees growth, decreases fruit quality, and destroys the garden in popular year. Owing to the lack of effective preventive measures, the disease is not controlled well and the pear industry still faces serious threat. Our research mainly analyzes the virulence differentiation for the pathogen of pear Valsa canker, sequences transcriptome data of two different virulence strains, and evaluates the resistance of Pyrus germplasm accession to Valsa canker. The datas could provide potential controls of the exacerbated disease and guarantee the safety in pear production. The results were as follows:1. The plates with pathogen of pear Valsa canker were inoculated on excised twigs, shoots, leaves, and fruits of pear (Pyrus pyrifolia cv. Hohsui), respectively, which were wounded by different methods. Two pear cultivars (P. pyrifolia cv. Hohsui and P. communis cv. Le Counte) were employed to determine the reliablest methods through inoculating with virulence known strains of the pathogen. The results showed that the incidence rate of inoculated shoots, including wounded by around ahearing, holing, ten times pricking and scalding hole were100%. However, others wounds by scaring bud, scalding, and three times pricking were15%,40%, and55%, respectively. The lesion lengths of the shoots wounded by the former four treatments were significantly bigger than that of the latter three. The lesion sizes on the leaves wounded by different methods, including pricking one time, three times, six times were siginificant differences. In inoculated twigs and fruits, there were no significant differences between the lesion sizes of the same materials wounded by all treatments. The results of the tests on determining the reliablest method showed that it was consistent with the differences of actual virulences of the strains that of strains inoculated on excised shoots pearused holing method. It was suggested that the method could employ to determine the virulence of the strains causing pear Valsa canker in laboratory because of obtained rapid and stable datas.2. To analyze the relationship between the source and virulence differentiation of the strains, all strains isolated from5kinds of pear systems and14provinces were inoculated on shoots of pear (Pyrus communis L. cv. Abate Fetel, P. pyrifolia Burm.f. Nakai cv. Hohsui, P.bretschneideri Rehd. cv. Yuluxiang, P. ussuriensis Maxim, cv. Nanguoli and P. sinkiangensis Yii. cv. Kuerlexiangli) using holing. The result showed that there was a significant difference among the lesion lengths caused by the strains obtained from cankers on different systems pear trees and provinces on different varieties. There was a difference on lesion lengths on pears were caused by the same strain. According to the strength of comprehensive pathogenicity of strains on different pear varieties, the strains could be divided into three types including16strains with strong pathogenicity (17.6%),70strains with middle pathogenicity (76.9%) and5strains with weak pathogenicity (5.5%). There were significant differences in the proportions of the pathogenic types of the strains from different areas and hosts.3. Using the second generation sequencing technology, we conducted transcriptome assembly analysis of the total RNA, which was extracted from strong virulent strain F-HN-6and weak virulent strain F-HN-2a-1.The results showed that there were6323differentially expressed genes including2816up-regulated genes and3507down-regulated genes of strong virulent strain F-HN-6relatively weak virulent strain F-HN-2a-1. GO function analysis showed that genes associated withoxidation-reduction process, catalytic activity and carbohydrate catabolic process had higher proportions. KEGG pathway enrichment analysis of differentially expressed genes showed that the genes associated with metabolic pathways, biosynthesis of secondary metabolites and starch and sucrose metabolism were significantly enriched.4. The resistance of a total of211samples of Pyrus germplasm to Valsa canker was evaluated by inoculating detached shoots in the lab with conidial suspension and mycelia plugs of Valsa mali var. pyri. The results indicated that the difference between the disease auti-invasion (17.5%) and auti-expansion (35.1%) was significant among the examined germplasm accessions. The disease auti-invasion and auti-expansion of the same germplasm accession in response to the pathogen was significantly different, and the consistent resistance accounted for30.3%while the inconsistent69.7%. For all of the germplasm accessions, highly resistant (HR/HR), resistant (R/R), Moderately (M/M), Susceptible (S/S), and highly susceptible (HS/HS) of the disease auti-invasion and auti-extension to the pathogen was1.4%,4.7%,12.3%(M/M),10.9%(S/S) and0.9%, respectively. According to comprehensive evaluation for the resistance, a total of ten resistance materials(R/R), three highly resistance materials (HR/HR) and two highly susceptible materials (HR/HR) were obtained in this experiment. |
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