大豆是人类油脂和优质蛋白的重要来源，是我国重要的粮油及饲料作物。近年来我国大豆的需求量不断攀升，但国内大豆产能不足，对外进口的依存度高达80%。我国大豆平均亩产水平在130公斤，尚有很大的提升空间。大豆疫霉引起的大豆疫霉根腐病是限制大豆产能的一个重要病害，尤其是2020年以来在我国大豆种植面积最大的东北主产区（约占国内总面积的64%）再次呈现暴发的趋势，而筛选使用抗病品种是防控大豆疫霉根腐病最为经济有效的防治措施。本研究依托国家大豆良种攻关项目，鉴定了2022-2023年收集的353份大豆新品种(系)对大豆疫霉的抗病性，筛选出一批综合抗性较好的大豆种质。同时，为监测国内大豆疫霉菌的毒力组成，本研究于2022-2023年对全国发病田块收集土壤或病株进行大豆疫霉的分离与致病型测定，以期为抗病资源的筛选提供参考依据与菌株资源。

主要研究内容如下：

2022-2023年国家良种攻关大豆新品种(系)对大豆疫霉的抗性鉴定：为鉴定2022-2023年国家良种攻关项目提供的353份大豆新育品种(系)对大豆疫霉根腐病的抗性，利用5个不同毒力型的代表性大豆疫霉菌株，采用大豆黄化苗下胚轴创伤接种法进行室内接种，根据制定的评价标准判定供试大豆品种(系)对单菌株的抗感类型和对多菌株的综合抗性等级。353份大豆品种(系)对5个大豆疫霉菌株共表现出20种反应型，对不同菌株表现为中抗以上的比例为33.1%~97.7%，其中抗强毒力菌株PsJS2的品种(系)数量最少，仅67份。与2022年相比，2023年中感及以下（0~2级）的品种(系)占比从37.7%下降至33.1%，抗病及以上（4~5级）的品种(系)占比从39.7%上升至51.6%。结合实验室2015-2021年的数据进行综合分析，2015-2023年间1406份品种(系)的综合抗性等级平均值从2015年的1.9（中感以下）逐步上升到2023年的3.2（中抗以上），综合抗性为3~5级（中抗及以上）的品种(系)占比从32.6%上升至66.8%，供试大豆品种(系)对大豆疫霉的抗性水平呈现逐年升高的趋势。2022-2023年综合抗性4~5级（抗病或高抗）的品种(系)共141份，冀豆、中作、中黄、周豆、漯豆、科豆、皖豆等7个系列的品种(系)各有5份以上，综合抗性5级（高抗）的品种(系)有52份，其中，冀豆、中黄、周豆、中作等4个系列的品种(系)各有4份以上，表明我国具有丰富的抗大豆疫霉根腐病资源。

大豆疫霉菌的分离及毒力与药剂敏感性测定：为明确我国大田环境中大豆疫霉菌的毒性组成，本研究于2022-2023年从黑龙江、江苏等地采集发病地块的病株61份、土壤样本64份，分别利用病组织分离和土壤叶碟诱捕的方法成功分离出68株大豆疫霉菌。利用下胚轴创伤接种的方式在13个鉴别寄主上进行收集菌株的毒力型鉴定，共得到51个不同的毒力型。68个菌株对Rps3c和Rps2两个抗病基因的毒性频率超过70%，提示含有此基因的大豆品种逐渐失去防效，含Rps1a、Rps1c、Rps3b和Rps7的品种对供试菌株的抗病频率较高。从黑龙江地区菌株的不同分离方式来看，分离自病株的大豆疫霉群体相较于土壤强毒力菌株分布更多，毒力多样性更丰富，分离自病株的大豆疫霉中13.5%的菌株可克服10个及以上的抗病基因，分离自土壤的大豆疫霉中96.8%的菌株克服基因数在5个及以下。选用5 μg/mL的精甲霜灵药剂进行抗药性测定，68个大豆疫霉菌株在含药平板上的生长量与对照（不含药平板）平均比值约为7%，均表现为敏感。从田间分离的68株大豆疫霉菌株中，选择10个不同来源和毒力的菌株对筛选到的10个高抗品种和3个高感品种的抗病性进行验证，发现其中9个高抗品种依旧具有高抗病力，初步表明实验室前期构建的大豆疫霉鉴别菌株系仍然可用于大豆品种对疫霉根腐病的抗性鉴定。

综上所述，本研究通过鉴定大豆新品种(系)对大豆疫霉的抗性，以及大豆产区田间大豆疫霉的分离、毒力测定及精甲霜灵抗药性分析，为大豆抗疫霉根腐病的品种选育与布局利用提供了参考。

Soybean is an important source of human fats and high-quality protein and is an important grain, oil and feed crop in China. In recent years, China's soybean demand has been rising, but the domestic soybean production capacity is insufficient, and the dependence on imports is up to 80%. China's average soybean yield level is 130 kilograms per mu, but there is still a lot of room for improvement. Soybean root rot caused by Phytophthora sojae is an important disease limiting soybean production capacity, especially since 2020 , China's largest soybean planting area in the northeast of the main production area (about 64% of the total area of the country) again showed an outbreak of trend, and the screening and use of disease-resistant varieties is the most cost-effective prevention and control of soybean root rot control measures. Relying on the National Soybean Variety Research Project, this study identified 353 new soybean varieties (lines) collected in 2022-2023 for their resistance to Phytophthora sojae , and screened out soybean germplasm with better overall resistance. At the same time, to monitor the virulence composition of Phytophthora sojae in China, this study collected soil or diseased strains from diseased fields across the country for isolation of Phytophthora sojae and determination of pathogenicity phenotypes in 2022-2023, to provide a reference basis and strain resources for the screening of disease-resistant resources.

The main research contents are as follows:

Identification of new soybean varieties (lines) with resistance to Phytophthora sojae in the National Soybean Variety Research Project, 2022-2023: In order to identify the resistance to the soybean Phytophthora root rot in 353 new soybean varieties (lines), five representative strains of Phytophthora sojae of different virulence types were used for inoculation indoors by using the modified etiolated hypocotyl-slit inoculation method, and resistance grades to single strains and multiple strains of the fungus were determined according to the evaluation criteria developed. According to the evaluation criteria, the resistance types of soybean varieties (lines) to single strains and the combined resistance grades to multiple strains were determined. 353 soybean varieties (lines) showed a total of 20 reaction types to five strains of Phytophthora sojae, and the proportion of those that showed more than moderate resistance to different strains ranged from 33.1% to 97.7%, with the lowest number of varieties (lines) resistant to the highly virulent strain PsJS2 at only 67 copies. Compared with 2022, the proportion of varieties (lines) with moderate susceptibility and below (grade 0-2) decreased from 37.7% to 33.1% in 2023, and the proportion of varieties (lines) with resistance and above (grade 4-5) increased from 39.7% to 51.6%. The average of the comprehensive resistance grade of the 1,406 varieties (lines) during the period of 2015-2023 increased from 1.9 (moderate susceptibility and below) in 2015 to 3.2 (above medium resistance) in 2023, and the proportion of varieties (lines) with a comprehensive resistance grade of 3-5 (medium resistance and above) increased from 32.6% to 66.8%, with the resistance level of the soybean varieties (lines) to soybean blight for testing each year showing a gradual trend of increasing. In 2022-2023, there were 141 varieties (lines) with comprehensive resistance level 4 to 5 (disease resistance or high resistance), with more than 5 varieties (lines) from each of the 7 series of Jidou, Zhongzuo, Zhonghuang, Zhoudou, Luodou, Kedou, and Wandiy, and 52 varieties (lines) with comprehensive resistance level 5 (high resistance), indicating that China has abundant resources of resistance to soybean Phytophthora root rot.

Isolation, virulence proportion and agent sensitivity of Phytophthora sojae: In order to clarify the virulence composition of Phytophthora sojae in China's field environments, 61 diseased plants and 64 soil samples were collected from the diseased plots in Heilongjiang and Jiangsu in 2022-2023, and 68 strains of Phytophthora sojae were successfully isolated by using the methods of disease tissue isolation and soil leaf disk trapping, respectively. The virulence phenotypes of the collected strains were identified on 13 identified hosts using hypocotyl trauma inoculation, and a total of 51 different virulence phenotypes were obtained. The virulence frequency of 68 strains against the two resistance genes, Rps3c and Rps2, was more than 70%, suggesting that soybean varieties containing this gene gradually lost their effectiveness against the disease, and varieties containing Rps1a, Rps1c, Rps3b, and Rps7 had a higher frequency of resistance to the strains for testing. From the different isolation methods of strains in Heilongjiang, the isolates from diseased plants had a greater distribution and richer virulence diversity compared with soil strongly virulent strains, and 13.5% of isolates from diseased plants could overcome 10 or more resistance genes, while 96.8% of the isolates from soil overcame 5 or less genes. When 5 μg/mL mefenoam was selected for resistance determination, the average ratio of the growth of 68 soybean blight strains on the drug-containing plate to the control (non-drug-containing plate) was about 7%, and all of them were susceptible strains. From the 68 strains of Phytophthora sojae isolated in the field, 10 strains with different sources and virulence were selected to verify the resistance of 10 highly resistant varieties and 3 highly susceptible varieties screened, and it was found that 9 of these highly resistant varieties were still highly resistant to the disease, which indicated that the Phytophthora sojae discriminatory strains constructed by the laboratory in the previous period could still be used for the identification of soybean varieties resistant to soybean Phytophthora root rot.

In summary, this study provides a reference for the selection and layout utilization of soybean varieties resistant to Phytophthora root rot by identifying new soybean varieties (lines) resistant to Phytophthora sojae, as well as the isolation of Phytophthora sojae in the field of soybean production areas, determination of virulence, and analysis of mefenoam resistance.