Evaluation Of Clubroot-Resistance Of Rapeseed Varieties And Detection Of Soil-Born Plasmodiophora Brassicae In Hunan

Oilseed rape is an important oil crop and economic crop in China,rape clubroot is a root disease caused by Plasmodiophora brassicae Woron.In recent years,the occurrence areas of clubroot in Hunan is increasing,which has become a serious threat to the development of oilseed rape industry.Since the existence of many different physiological races of P.brassicae,there are significant differences in the resistance of rape germplasm and existing rape varieties to different physiological races,and long-term planting of single resistant varieties caused the loss of resistance.Therefore,this study was mainly focused on evaluation of the clubroot-resistance for rapeseed varieties and monitoring of soil-born P.brassicae in Hunan.The main results are as follows.The resistance of 100 cultivated rapeseed varieties in Hunan was evaluated by artificial inoculation in greenhouse and natural induction identification in Yuanling and Hengyang disease nursery.Results showed that 57 cultivars were resistant to P.brassicae,and 8 cultivars showed immunity were Changxiangyou 3,Liangjing 811,Jinyouza 605,Jujiayouwang,Qingyou 3,Deaiyou 558,Zheyou 50 and De Zayou 903,etc.In the field natural induced resistance identification experiment of the above 100varieties,the proportion of varieties with strong resistance in Yuanling and Hengyang have 45 cultivars and 8 cultivars,respectively.Based on the results of greenhouse and natural induction resistance identification,seven resistant rapeseed varieties including Liangjing 811,Zhongyanyou 1,Huaxin 402,Fengyou 737,Baoyou 150,Youyan 9and Jiayou 1427 were screened,which could be widely planted in Hunan province.Based on a set of real-time fluorescence quantitative PCR detection system was established to accurately quantify the amount of dormant spores in soil,two hundred and fifty-nine soil samples collected from 36 clubroot areas were detected by real-time fluorescent quantitative PCR using specific primers GZ10/GZ11,and the risk level of the occurrence of clubroot was assessed according to the content of P.brassicae in the soil.Result showed that the content of P.brassicae in the field soil were between10~4to 10~5spores/g soil sample.The risk grades of different regions were evaluated.Among these,4 regions were in extremely high risk areas,most of which were in Huitong County of Huaihua city.There were 8 regions in high risk areas,17regions in medium risk areas,and 7 regions in low risk areas.The p H value,available potassium content,alkali-hydrolyzable nitrogen content,organic matter content and exchangeable calcium content of 45 soil samples from different areas were measured,and their relationship to the disease index of rape clubroot was explored.Results showed that the p H value,available potassium content,alkali-hydrolyzable nitrogen content,organic matter content and exchangeable calcium content were significantly different in different regions.Soil p H value,alkali-hydrolytic content,available potassium content and organic matter content were positively correlated with the disease index,while exchangeable calcium ion and bacteria content were negatively correlated with the disease index.The p H value of soil and exchangeable calcium content might affect the occurrence of clubroot cooperatively.