| Plasmodiophora brassicae is the pathogen who cause clubroot fungus.clubroot is one one of the most serious diseases on cruciferous plant.and is also a worldwide disease.The practice proved that planting blast resistance cultivars is an economical and effective way to control the disease.But there exists differentiation of physiological races in P.brassicae,the identification of physiological races is directly related to the eddective breeding for clubroot-resitant crops.So it makes great sense to undertake the studies of pathogenic races of china,the result is important to breeding and rational distribution of disease-resistant varieties.At present,the general international disease identification systems(e.g.Williams hosts system)have their limitations on their application in our country:first,it is difficult to obtain massive seeds for the total hosts in China;second,the general disease identification systems can not make cleaely distinction for the physiological races of china.Therefore,it is necessary to develop a set of differential hosts for China's P.brassicae.This study is committed to establish a new differential hosts system,which is suitable to China's situation,two identification systems have been built "Black and white" differential hosts system and "threshold"hosts system.On the selection scope of hosts,the requirements for the new differential hosts are less hosts,simple,sensitive and highly accurate.The results of the study are as follows:1.Preliminary screening of hostsAccording to the literatures,compatible Brassica plants and 9 regions of the clubroot materials in this country have been Collected.the resistance response of the hosts was obtained through the natural inoculation and the laboratory inoculation test.After preliminary screening,several potential host plants were obtained:B-CFH,B-HT,B-YQ,B-CL,B-QG,B-FC,B-QQ,B-HC,B-CF,B-CC,B-XY,G-11,B-60,B-DX,G-ZX.2.Building"black and white" differential hosts system"Black and white" is the difference on the "quality",according to whether symptoms showed on the hosts after inoculation.Four varieties B-CFH,B-HT,B-CL,B-QG were selected from the primary screening hosts,who have difference in"quality".These varieties form the"Black and white" differential hosts.This differential hosts can separate and classify 9 regions of the clubroot materials.This differential hosts can also separate 3 different physiological races,which were identified with Williams system.And cmpared with Williams host system,"Black and white" system's standard is clearer,the error is smaller.3.Building" threshold"differential hosts system"Threshold"That is using a disease index as a threshold,namely the difference on the"amount".This system using DI = 30 as threshold,?30 is susceptible,<30 for disease resistance.Four varieties G-ZX?G-11?B-CC?B-XY were selected from the primary screening hosts,who have difference in "amount"?These varieties form the" threshold " differential hosts.This differential hosts can separate and classify 9 regions of the clubroot materials.But this differential hosts can only separate three different physiological races into two races,which were identified with Williams system.4.Histopathological observation of the host system.Histopathological were observed in"Black and white" differential hosts,The results show that the hosts can clearly show the organizational structure differences,these differences can show the resistance.We can see the severity of the damage of the root vascular bundles and cortex tissue.This means that the four varieties have specific reaction of resistance with different strains of P.brassicae.The study show the rationality of "black and white" in two aspects of disease index and histopathological. |
PDF Full Text Request