| Cucumber brown spot disease caused by Coiynespora cassiicola is seriously occurring in the cucumber production,and has a significant impact on the cucumber yield and quality.Research had been performed systematically on isolates collected form Liaoning,Hebei and Shandong provinces in such aspects as culture traits,pathogenicity differentiation,genetic diversity and sensitivity to fungicides.The research results were as follows:1.In total 106 isolates of Corynespora cassiicola from cucumber leaves collected from Liaoning,Heibei and Shandong provinces had been isolated and purified.It had also been systematically implemented to study the culture traits for the 106 isolates.Under the uniform culture condition(at 28? on the PDA without light)for all the 106 isolates,hypha growth rate could be divided into fast type,moderate type and slow type,with the isolate number of 65(61.32%),37(34.91%)and 4(3.77%),respectively;the aerial hyphae were divided into thickset type and scanty type,with respective isolate number of 88(83.02%)and 18(16.98%);these fungal colony colors consisted of dark blackish green,dark brown,grey,light grey and white,with grey and light grey in the majority;the pigment secretion comprised earthy yellow,light red and claret-red and no pigment,in which there were 65(61.32%)isolates secreting no pigment.There exhibited higher sporulation capacity among the 106 isolates,and the average sporulaiton capacity was situated in the scope of(2.45±0.20)×105 spores per square centimeter,and this capacity was evidently related to the type of aerial hyphae.2.The optimal culture conditions had been studied for 4 isolates inclusive of LJP-2,SJN-3,SQD-land HHJ-1 which respectively displayed distinct characteristics and geographically different origins.In terms of culture medium,PDA was the most suitable for SJN-3,SQD-1 and HHJ-1,while LJP-2 grew best in the PSA.On the whole,4 isolates all grew normally and harmoniously at 28? but relatively slower in much higher or lower temperature in which their colonies would turn transparent or white and pigment secreted abnormally.The completely lasting light promoted colony enlargement and hyphae extension for LJP-2,SJN-3 and SQD-1,whereas HHJ-1 grew faster and better in complete darkness but it got suppressed by light.LJP-2 grew best in lactose and worst in maltose,SJN-3 grew best in mannitol and worst in starch,while both SQD-1 and HHJ-1 grew best in mannitol and worst in maltose.Peptone and yeast extract powder contributed the 4 isolates to grow fast and vigorously,while(NH4)2SO4 imposed restrictions on the 4 isolates.3.The pathogenicity differentiation had been studied for 106 isolates collected from Liaoning,Hebei and Shandong provinces by using a set of identifying cucumber cultivars with steadily evident resistance and susceptibility including Jinyou 38,Xinlianyan 4,Deruite 10 and Shandongmici.The pathogenicity for all tested isolates could be divided into 3 types including pathogenically strong,moderate and weak properties,with the corresponding isolate number of 29(27.36%),70(66.04%)and 7(6.60%)respectively.Isolates from Liaoning displayed strong or moderate pathogenicity,however,all the 3 pathogenicity types appeared in the isolates from Heibei or Shandong,and most of isolates from Heibei belonged to moderate or weak pathogenicity type,nearly all of those from Shandong belonged to strong or moderate pathogenicity type.4.By means of making comparison for the ITS and analyzing dendrogram based on ISSR data,it had been fulfilled to perform research on genetic diversity for 92 isolates representative of geographic origin and pathogenicity types.There was no less than 98%identity between all the supplied isolates and the model isolate(KP211426).and they all were clustered into one clade.In the results of ISSR marking,in total 74 polymorphic bands had been amplified by 6 ISSR primers with the polymorphic frequency of 90.54%.The genetic coefficient of similarity for the 92 isolates was ranging from 0.76 to 0.97,showing that there were some differences in genetic relationship among the isolates.92 isolates were divided into 4 ISSR Groups(IG)at a coefficient of 0.82.It had been confirmed that the genetic diversity for the isolates was not significantly related to geographic origin but was close to the pathogenicity.Isolates from IG I belonged to strong or moderate pathogenicity type.Isolates of 3 pathogenicity types could exist in IG III with most isolates belonging to strong and moderate pathogenicity type.Isolates from IG IV belonged to moderate and weak pathogenicity type.5.It was administered to study the virulence of 3 sorts of fungicides to 30 typical isolates and the efficiency of such fungicides in controlling cucumber brown spot disease in the field trial.There were some differences in the sensitivity among 30 isolates to each fungicide.By and large,isolates were most sensitive to Thiram Zitox,more sensitive to Pyraclostrobin,and sensitive to Kasugamycin in distinctly different extent.The EC50 of Thiram Zitox,Pyraclostrobin and Kasugamycin was respecitively during 0.017?0.309?g/mL,0.022?0.759?g/mL and 1.167?g/mL?181.948?g/mL.The sensitivity to fungicides for the isolates was not close to geographic origin,pathogenicity and genetic groups but quite close to hyphae growth type and aerial hyphae type.On the whole,isolates with scanty hyphae were more sensitive to fungicides than those with thickset hyphae.The results of control efficiency in the field trial showed that Thiram Zitox was more effective in controlling cucumber brown spot disease than Pyraclostrobin.The controlling rate for Thiram Zitox at dilution concentration of both 1000-fold and 1500-fold was respectively significantly more than that of Pyraclostrobin in the two replicated trials. |
PDF Full Text Request