Effect Of Different Inoculation Methods Of Plasmodiophora Brassicae Resting Spores On Disease Severity

Brassica clubroot is a soil-borne diseases around the word, any of the susceptible cruciferous plants can be infested.The disease was first discovered in the Mediterranean Sea in the West Bank and southern Europe,and nowdays, the disease has been found in Europe,Asia,Japan and Taiwan for a long time and generally serious. The disease has spreaded quickly after introduced to china. In this study,Clubroot pathogen collect from Kangding Sichuan Province was used for the study of root hair infections of China cabbage.Observed the infected root hairs by microscope to understand the morphological changes root hair infection.Compare the difference of disease indexs according to the three different standards of disease grading. Studied the concentration and inoculation methods on the effect of the incidence and disease index.And the impact of inoculated at different growth stages on morbidity and disease index.Main results were as follows:1. Screening of dispersants on resting sporeIt is hard to count resting spores and observe their morphological characteristics because of the agglutination of resting spores. Screening 5 dispersants and 0.1% Sodium lignosulphonate was selected as the best one.2. The phease of root hair infectionsThe pathogen of Plasmodiophora brassica is an obligate parasite,and its life cycle consists of two phases.The development of primary plasmodia occur in all hosts. Observed the infected root hairs by microscope and found the development of pathogen was classified into five categories:plasmodia, young zoosporangia, mature zoosporangia,zoosporangia releasing secondary zoospores,and death or cessation.3. Effect of different inoculating concentration on root hair infectionObserving under the microscope and find that in root infection the numbers of infected root hair were rise with the increase of inoculation concentration. Inoculating resting spores for 24h,hair infections was been observed first time.When the inoculation concentration was low,root hair infection almost can not been observed. The highest rate of root hair infection occurred when the inoculation concentration was 1×105～109·mL-1.4. Impact of different inoculating concentrations and methodsCompared with 3 inoculation methods:mixture of resting spores and soil, infusion spore suspension in the rhizosphere surface,and dipping the root of seedlings with spore suspension. Inoculating resting spore of Plasmodiophora brassica with different concentrations,the result showed that:inoculating with different methods,the best inoculation were not the same,they were 1×106 spores·mL-1,1×107 spore-s·mL-1,and 1×107 spores·mL-1.5. Impact of different standards of disease gradingAccording to the 3 different standards of disease grading to calculate disease indexs and found that there is a big difference among them. The disease indexs were:4 grades>9 grades>6 grades.6. Inoculating and investigating in different growth periodsThis study found that inoculating 10 days-old seedlings,there would be high mobidity and disease index.Comparison of disease incidence in different growth periods,the result showed that the morbidity at the 30th days was much higher and more stable,at the 50th was the highest.At the 60th days,some of the seedlings had rotten root. Therefore,the best investigating time was 30～50 days after inoculating.