| Powdery mildew (PM), caused by Podosphaera xanthii (formerly known as Sphaerotheca fuliginea Schlech ex Fr.Poll.) or Golovinomyces cichoracearum (formerly known as Erysiphe cichoracearum DC ex M/erat.), limits the production of cucumber (Cucumis sativus L.) throughout the world. In China, Podosphaera xanthii has been identified as the primary cause of PM in both the greenhouse and field cucumber cultivation. The PM pathogens have a wide host range and are readily detached and borne by air currents. According to the investigation, the severe PM infection occurred before the flowering stage could reduce the output of the fresh cucumber fruits by 30% to 50%. Developing resistant cultivars would provide an economic and evironment-friendly control strategy. Although former studies have showed that the resistance or susceptibility to PM infection varies among the cucumber cultivars, up to now, there have been few evidences for the existence of the single gene-controlled high resistance to PM in the surveyed cucumber varieties. Thus, it would be a hard task to breed high resistance cucumber lines to PM by traditional breeding method. To research the principle of PM resistance and locate the resistance gene, which is very important for actualizing molecular-marker assisted selection breeding and cloning resistance gene in the future.1.By means of leaf-inoculation by two repetition test, the resistance of 120 germplasm of cucumber to cucumber powdery mildew were identified and evaluated with resistance index. The results indicated that among the tested 120 materials, high-resistant, mid-resistant and mid-susceptive, susceptive materials were 17, 82 and 21 strains, respectively. High-resistant materials come from ten of China cucumber materials, in addition, including each two from China Taiwan and Japan, each one contribute by America, Holland and Philippine. The important resistance disease informations about cultivating elicit cucumber variety were offered through the experiment.2.We constructed F6∶7 population from resistant line S06 as male parent cross with sensitive line S94(Northern China open-field type) as female parent. The linkage map used in this study using molecular marker technique constructed, includes 257 molecular markers [206sequence-related amplified polymorphisms (SRAP), 22 simple sequence repeats (SSR), 25sequence characterized amplification regions (SCAR), 1 sequence-tagged site (STS) and 3 morphologic traits ] with the total map length of 1005.9 cM and a mean marker interval of 3.9 cM, which is suitable for QTL analysis.3. PM is an economically important disease of cucumber caused by the obligate biotrophic pathogen, Podosphaera xanthii, in greenhouse and field. In this study, a resistant breeding line S06 and a susceptible cucumber inbred line S94 and their F2:3 populations were used to investigate PM resistance under seedling spray inoculation in two growing seasons and leaf disk infection in one season. QTL analysis was undertaken based on a constructed molecular linkage map of the corresponding F2 population using composite interval mapping. Five QTLs (pm1.1,pm1.2, pm2.1, pm2.2 and pm5.1) for PM resistance were identified and located on linkage groups (LG) 1, 2 and 5, explaining 3.4～45% of the phenotypic variation. Three consistent QTLs (pm1.1, pm2.1 and pm5.1) were detected under the three test conditions.4. S06 and S94 and their F6:7 populations were also used to investigate PM resistance under seedling spray inoculation in 2005/Autumn and 2006/Spring. QTL analysis was undertaken based on a constructed molecular linkage map of the corresponding F6 population using composite interval mapping. A total of four QTLs (rpm1.1, rpm2.1,rpm4.1 and rpm6.1) for PM resistance were identified and located on LG 1, 2, 4 and 6, explaining 5.2%～21.0% of the phenotypic variation. Three consistent QTLs (rpm1.1, rpm2.1 and rpm4.1) were also detected under the two test conditions.The rpm6.1 was only identified in 2005/Autumn. The total phenotypic variation explained by the QTLs was 52.0% and 42.0% in 2005/Autumn and 2006/Spring,respectively.According to the data from the two different generations collectively, only two QTLs were consistent on LG1 and LG2, respectively. The position of additive alleles and phenotypic variation of these QTLs were variance between F2:3 and F6:7.Disease control relies mainly on the extensive use of fungicides, with the risk of development of resistant pathogen strains. To obtain green food, the replacement of fungicides by effective and environmentally friendly methods is the major way forward. Vitamin B1 was also reported to have medicinal uses in Arabidopsis and rice. In the present experiment, we invest -igated the efficacy of Vitamin B1 which protected cucumber seedling against the cucumber powdery mildew fungus and the resistance disease mechanism for Vitamin B1 operation.1.Pre-treatment of the first leave of cucumber seedlings with Vitamin B1, four hours prior to inoculation with powdery mildew, reduced the disease index by over 38% at 50 mmol/L ,which was confirm prime treatment concentration.2.Using 50 mmol/L Vitamin B1 and powdery mildew(Podosphaera xanthii ) to dispose cucumber first true leaf and take hearts leaf RNA according to time level, pathogensis-related defense marker gene[pathogenesis-related protein-1a, (PR-1a) acidic peroxidase(POX), , phenylalanine ammol/Lonia -lyase (PAL) ]expression with contrast control(water treatment,0h) were checkout through real time's fluorescence PCR. Results showed that in inocul -ated plants that measured increases in POX, PR-1a and PAL expression appeared highest at 12h,48h and12h post treatment,respectively (an approxi -mate 3.1-fold increase in PR-1a expression, 4.9-fold increase in POX expre -ssion and 2.5-fold increase in PAL expression). The results showed that pre -treatment of cucumber seedlings with Vitamin B1 can gain resistance to powdery mildew through systemic acquired resistance (SAR) track. |
