Screening Of Molecular Markers For Downy Mildew Resistance Introgression Line Of Cucumis Hystrix-C. Sativus And Analysis Of Programmed Cell Death

In recent years, the new cucumber varieties of downy mildew resistance only involves a few elite parent materials, because of its narrow genetic basis and the lack of resistant sources in cultivars. The limited interspecific variation has constrained cucumber resistance breeding of downy mildew. Recent appearance of new physiological races resulted in the new downy mildew resistant genes urgently needed to ensure cucumber production. It is an effective way to transfer the resistance gene from Wild species which can get a breakthrough of cucumber breeding.Cucumis hystrix Chakr. is an rare wild species native to China which discovered by professor Chen Jinfeng at 1989. It is rich source of useful genes for the improvement of cultivated cucumber. Following by the successful interspecific hybridization and chromosome doubling, the allotetraploid (2n=38) was further backcrossed to cucumber to get allotriploid, monosomic alien addition line, alien translocation line, and introgression line, etc. Among the introgression lines 5211S with high resistance to downy mildew was identified, showing great potential for cucumber downy mildew breeding.To facility 5211S with great potential, the Self-pollination purification, inheritance and markers linked to downy mildew resistance gene in 5211S were studied. Furthermore, some preliminary explorations on the programmed cell death involved in downy mildew resistance were also carried out.1. Purification of downy mildew resistant introgression line 5211S of Cucumis hystrix-C. SativusIn this study, downy mildew resistant introgression line 5211S of Cucumis hystrix-C. Sativus were evaluated by natural inoculum during the growing season in the filed.12 introgression individuals were selected which resistance is stable, named it ILDM10-1 to ILDM10-12 (BC1F8). ILDM10 is high resistance to downy mildew, also with little or no sporangia. This is important to cucumber downy mildew resistance breeding. Identification results also show that the cucumber virus disease has a strong antagonistic effect on downy mildew. This is a new direction of biological control of cucumber downy mildew.2. SSR markers for downy mildew resistant introgression line ILDM10-4 of Cucumis hystrix-C. SativusAn F2 segregating population derived from the cross between'Changchun Mici'(high susceptible)×ILDM10-4 (high resistance) was used to study the inheritance of the downy mildew resistance. The result confirmed a single recessive gene conferring resistance in ILDM10-4. With screening of polymorphism of 534 SSR markers by Bulked Segregant Analysis (BSA), three polymorphic co-dominant markers SSR00772, SSR03529, SSR15321 were found to be linking to the downy mildew resistance gene(ILdm), with a distance of 3.8cM,6.0cM,16.7cM, respectively.3.Expression of programmed cell death genes in cucumber downy mildew resistant introgression line ILDM10-4Downy mildew resistant introgression line ILDM10-4 of Cucumis hystrix-C. Sativas was selected as materials. According to the reported Arabidopsis EDR1, EDR2 gene, the highest homology genes (Csa001463 and Csa015689) were screened in the cucumber genome. Two pairs of specific primers designed according to the FASTA sequences were used to analysis the expression of EDR1 and EDR2 in different organs, and under abiotic stress by Semi-qRT-PCR. In addition, the Expression patterns of EDR1 and EDR2 in response to P. cubensis, exogenous application of hormones and H2O2 were studied. The results showed that expression of EDR1 and EDR2 was respectively lowest in leaves and roots; High-temperature, low temperature, drought significantly inhibited the expression of EDR1, and only low-temperature inhibited the expression of EDR2; The expression of EDR1 was inhibited after infected by downy mildew. After 72h, the expression level recovered. The expression of EDR2 was very low before inoculation, and then progressive increased. The expression patterns of EDR1 in response to SA and H2O2 were similar. MeJA and ABA also had the similar impact models. The EDR2 expression patterns in response to four hormones were independent in each other.