Identification Of Molecular Markers Linked To Powdery Mildew Resistant Gene In Cucumber

Cucumber (Cucumis sativus L.) is globally and widely cultivated vegetable. In China, it helps to provide a year-round vegetable supply. Consequently, cucumber breeding is an important and international active work. Powdery mildew disease is one of the most serious disease in cucumber, but the identification of disease resistant gene is complicated. With the help of molecular markers, it is possible to perform indirect selection in cucumber breeding, which helps to improve the accuracy and efficiency in genetic analysis. It is important to establish the marker assisted breeding in cucumber disease resistance.A F₂ population from the cross of 'WIS2757' and '19032' is used as experiment material, 'WIS2757' ( resistant to powdery mildew ) is an American open field ecotype, '19032' ( susceptible to powdery mildew ) is an European greenhouse ecotype. These parents and their F₁, F₂ individuals were screened in powdery mildew resistance during the seedling stage. Firstly, we analysed the inheritance of powdery mildew resistance, secondly we identified AFLP molecular marker tightly linked to powdery mildew resistant gene in cucumber, at the end, we convert AFLP marker into SCAR marker.The following are the results I gained in this experiment.1. After screending the resistance to powdery mildew, we diveded 592 F₂ individuals in three parts, 35 inviduals are resistant, 106 inviduals are middle resistant, 456 inviduals are susceptible, the x² is 0.57, this ratio is accord with the ratio 1:3:12. The result showed that cucumber powdery mildew resistant genes were controlled by three genes (RRssII), a major recessive gene s, a dominant gene R and an recessive gene I. The gene s was the major gene, it decided the hybical resistance, R was basis of leaf resistance, it was expressed when s was homozygous. When recessive gene I was working, plants only expressed some parts of resistance, but I didn't influenced the expression of 5. The result is in line with the result of Shanmugasundarum et.al(1971) 2. In our study, 512 pairs (32 Pst I primers x 16 Mse I primers) of AFLP primers was used to screen the polymorphic between parents( 'WIS2757' and '19032' ) and their F₂ individuals. We got 255 pairs of primers that have polymorphic between 'WIS2757' and '19032', the ratio is 49.8%. In these primers, there are 93 pairs of primers screen polymorphic in parents, their F₂ resistance gene pool and susceptible gene pool (each pool has 10 F₂ individuals), the ratio is 18.2%. The primer pair 'p63-m51' can product one specific band 'p63-m51-384', it is tightly linked to main powdery mildew susceptible gene in cucumber, the genetic distance is 7cM.3. After sequenced the band, we found that no fragment is isogeny with it in NCBI date base. It shows that the DNA fragment was a new cucumber DNA sequence. According to the result of the DNA sequence, we designed several SCAR primers and successfully transferred it into SCAR marker, and this SCAR marker is also tightly linked to main powdery mildew susceptible gene in cucumber, the genetic distance is 7cM.