| Sclerotinia stem rot, a fungal pathogen disease, is also known as white mould. It is a worldwide soybean disease caused by the fungus Sclerotinia sclerotiorum(Lib.) de Bary infecting the host plants. 44 of soybean cultivars have been inoculated by 4 isolates of S. Sclerotiorum from different geographical regions and host plants for two consecutive years in the field in our research. A rapid and effective method for evaluation of resistance to Sclerotinia stem rot in soybean in the field has been established, and the anti-/ resistance of soybean cultivars to Sclerotinia stem rot was screened by the method. At the same time, it provides excellent germplasm for soybean breeding resistance to S. sclerotiorum. Moreover, genetic diversity among 32 isolates of S. sclerotiorum from different geographical regions and host plants was also studied by the method of SSR markers. The results were summarized as follows:1. Establishing a rapid and effective evaluation method for soybean resistance to Sclerotinia stem rot in the field. Four isolates of S. sclerotiorum from different geographical regions and host plants were cultured in the PDA culture medium. Mycelium from the culture was used for preparation of wheat seed inocula. The evaluation method for resistance to soybean white mould in the field was established by minimally invasive silver paper trussing inoculum on the soybean plants. This method has involved the inoculation of soybean in greenhouse and rape in the field. 44 of soybean cultivars were inoculated and screened for two consecutive years in the field. The results of statistical analysis showed that there was a significant difference both in the DSI and lesion length among the various soybean cultivars, and among the isolates of S. sclerotiorum, however no significant difference among the replicates. There was a significantly positive correlation between the DSI and lesion length (r = 0.8301, P<0.0001). It concluded that this method, inoculation and identification of the anti-Sclerotinia stem rot in soybean in the field, can effectively identify the pathogenicity of S. sclerotiorum and screen the resistance to S. sclerotiorum and provide excellent cultivars.2. Identificating and screening for resistance to Sclerotinia stem rot among soybean cultivars from mini-core collection. 44 of soybean cultivars were inoculated by four isolates of S. Sclerotiorum from different geographical regions and host plants in the field by the method above. After 2 years identification, we found that different soybean exist different resistance to S. sclerotiorum. There were 6 moderate resistant cultivars, accounting for 13.64%; 27 moderate susceptibility cultivars, up to 61.36%; 9 susceptibility cultivars, 20.45%; 2 high susceptibility I, 4.55%. Thus, soybean cultivar with resistance to S. sclerotiorum is rare. Six soybean cultivars show moderate resistance to S. sclerotiorum, such as HeFeng 24, Big Swan Egg, Ni Ding Hua Mei Bean, Niu Mao Huang, Big Soybean and May Soybean, in which DSI of cultivar HeFeng 24 is 22.38, and lesion length is 1.61 mm, showing a lowest value. These six cultivars could be used for soybean anti-S. sclerotiorum breeding. Consequently, we should screen soybean cultivar intensified in order to find the high resistance to S. sclerotiorum for its rarity.3. Different pathogenicity of S. sclerotiorum isolates from different geographical regions and host plants. The pathogenicity analysis of 4 isolates of S. sclerotiorum from different geographical regions and host plants shows that, isolate Heixi5 has the strongest pathogenicity with 49.32 in DSI and 5.93 mm in lesion length from the soybean field of Wudaoqiao village of Xifeng town, Heilongjiang province. Isolate Heirao24 from the 24th team of Raohe farm also in Heilongjiang province and isolate Qin24 from the oilseed rape field of Qinghai province are second in pathogenicity. Isolate Hef50 from the oilseed rape field of Anhui province is the weakest, whose DSI was 39.02 and the lesion length was 3.65 mm. In conclusion, isolate Heixi5 is the most effective to screen the resistance to S. sclerotiorum in soybean.4. Analysis of genetic diversity among different isolates of S. sclerotiorum. A total of 69 alleles were detected using 17 SSR markers, with an average of 4.06. The primers AF377908 and AF377922 had the largest allele high as 8. While primers AF377903 and AF377925 had the least number as 2. The mean of polymorphism information content(PIC)was 0.56. The highest is primer AF377922 in 0.78. In cluster analysis, 32 isolates were divided into five populations. Most isolates from the same region were grouped in the same or a close population, which indicated that Sclerotinia genetic loci within populations are relatively consistent, but among populations vary significantly.
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