| Brassica napus is the main source of edible vegetable oil in China. In the terms of rape cultivation area and yield of rapeseed, our country ranks high in the world. Downy mildew caused by Hyaloperonospora parasitica is one of serious disease of rape, it had been found in all rapeseed-planting areas in the world. Under suitable conditions, about 10%~50% plants could be infected. In some severe cases the infection ratio may reach up to 100%. This rape disease used to cause 10 to 50 percents yield losses on every single plant. The serious impact of downy mildew on rape product and ecology can not be ignored. Now, chemical control was the main methods to control downy mildew, however, it did not work well, and it could bring environmental pollution. Breeding resistant varieties as the ideal method of prevention was on going, marker-assisted selection breeding can greatly shorten the breeding process, improve the efficiency of disease resistance breeding.This study ascertained the optimum conditions by studying the biological characteristics of the pathogen of downy mildew on B. napus. Then, after natural inducement in field, we selected disease-resistant varieties “35710” as resistance-parent.And a F2 population though the self-fertilize on F1 that crosses between resistance-parent 35710 and susceptible-parent 33463 was built. Next, we studied the resistance heredity rule of downy mildew. Furthermore, some SNPs of the resistance to downy mildew on rape were developed based on SLAF-seq and BSA. In order to facilitate the breeding for disease resistance, we designed some differential primers and transverted SNPs to SNAP markers. Finally, the functional annotation and enrichment analysis of disease resistance related genes are carried out, and the resistance genetic metabolic pathways were predicted. These will pave the way for the following function verification and gene clone analysis.The main research result is as follows: 1. The pathogen of downy mildew on rape is Hyaloperonospora parasitica. The relative humidity(RH) for spore germination is higher than 80%. The higher RH is, the bigger of germination rate is. The germination rate of spore is largest in the distilled water. The optimum germination temperature of the sporangium ranges from 15℃ to 18℃ and the optimum pH of the sporangium ranges from 6 to 7. The less quantity of Tween-20 in spore suspension is, the less inhibition effection to spore germination was. 2. After identification, the material “35710” was found to be highly resistant to downy mildew, the uniformity of disease resistance of F1 population indicated that this resistance was control by nuclear genes; The disease degrees from 0 to1 level was considered to be resistant, the level from 3 to 9 was considered to be susceptible. The statistical of the disease incidence of plants was used to study the inheritance of resistance, and through the fit test, and the results showed that the resistance was controlled by a single gene, and was completely dominant. 3. Molecular markers were developed by SLAF-seq technology and BSA method. Through association analysis, two non-synonymous SNPs associated with resistance of rape to downy mildew were obtained. According to these two SNPs, SNAP molecular marker was developed. After optimizing PCR system, primers 1LR1 and 2LR1 for resistance related markers BDsnp01-A and BDsnp02-G, and primers 1RR1 and 2RR3 for susceptible markers BDsnp02-C and BDsnp02-a were obtained. |
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