The Research Of Rapeseed Clubroot Control By Integrating Seedling Transplantation,Chemical Precision Employing And Resistant Cultivar Utilization

Rapeseed is the largest oil crop in our country.The rapeseed oil production tops in the vegetable oil and is of great significance to guarantee the yield and quality of rapeseed oil.Clubroot caused by Plasmodiophora brassicae Woronin.has become one of the most important diseases on rapeseed.Application of resistant cultivars is supposed to be the most economic and effective way to control the disease,but disease-resistant breeding progress is tardy and few resistant cultivars can be used in production.It is necessary to develop an integrated approach to manage clubroot.In this study,through the study on different transplanting date,seedling age and accurately employ of chemicals which may greatly influence the disease incidence,index and yield of rapeseed.Together with the study of disease investigation and resistant gene loci detection of 28 Chinese cabbage to different strains of P.brassicae,a comprehensive technology to control the clubroot disease and raise yield is explored.Results of the study are as follows:1.In greenhouse experiments,0,5,10 and 15-day-old rapeseed seedlings were inoculated with P.brassicae resting spores respectively.The clubroot disease was investigated at 30 days after inoculation.The results indicated that the disease incidence and index increased with the seedling growth both in greenhouse and the field.2.In field experiments,16~44-day-old rapeseed seedlings were transplanted weekly from October 7th to November 4th.Clubroot disease and rapeseed yield were investigated at harvest.The results showed that the clubroot disease incidence and index of early(October 7th to October 21st)transplanting rapeseeds was higher than the late transplanting rapeseeds.Considering the temperature of the day transplanted,lower average temperature leads to the lower disease incidence and index.Moreover,the yield of rapeseed was the highest when the seedlings were cultured at late September or early October and were transplanted at the end of October.Early seedling and transplanting made large yield losses because of the serious disease.On the other hand,late seedling and transplanting made a small quantity of yield losses,but delayed seedling and transplanting resuleted in less yield because of the short growth period.3.In field,transplanted seedlings were treated with fungicide cyazofamid,calcium cyanamide or combination of them.Clubroot disease was investigated at havest.The results showed that both application of calcium cyanamide(5g/plant)and cyazofamid(10 mg/plant)can efficively prevent from the disease,and the disease incidence of control was 33.3%.This resultssuggested that co-application of calcium cyanamide and cyazofamid can be as a new strategy for seedling transplantation,which will provide guidance for disease control and yield increase of rapeseed.4.The disease investigation and resistant gene loci detection of 28 Chinese cabbage to different strains of P.brassicae indicated that 27 cultivars showed resistance to some strains,while the Genwang F1 was susceptible to all strains.The best 10 cultivars including CR Chunfu showed resistance to all strains.12 cultivars such as CR-Liangchun showed susceptibility to only one strain,9 of which was susceptible to the strain(mixed race of 4,7 and 10)from Enshi.Molecular markers detection results indicated five CR loci including Crr2?Crr3?CRa?CRb?CRk.CRk were detected in 27 cultivars,among which CRk was common in resistant cultivars.Crr3 hybrid resistant locus was detected only in CR Chunfu.No CR loci were detected in the susceptible cultivar Genwang F1.