| In this study, we isolated 12 strains of Fusarium oxysporum f. sp. fragariae, which were isolated from strawberry greenhouse in Zhaoyuan City, Tengzhou City, Tai'an City and Linyi City, Shangdong Proeince. The resistances of 12 strains to six trizole fungicides and to four other fungicides were determined by using mycelium growth rate method, and compared the resistance level of these fungicides. The triadimefon-resistant strains of wild-type (ZY001) of F. o. f. sp. fragariae were selected on medium with the triadimefon, and we elected a high triadimefon-resistant strain as the field strain. The resistance developing of F. o. f. sp. fragariae to triadimefon and also the cross-resistance of each resistant strain were carried out. The physiological difference and biochemical difference between the triadimefon-resistant strains and the sensitive strain were compared.The results showed as follows:1. The EC50 values of propiconazole, difenoconazole, myclobutanil, diniconazole, tebuconazole, triadimefon, thiram hymexazol, thiophanate-methyl and carbendaizm to the 12 strains of F. o. f. sp. fragariae ranged from 0.8831 to 162.81, from 0.1623 to 9.5898, from 0.1307 to 9.0317, from 1.1969 to 60.927, from 0.1446 to 2.2586, from 0.1107 to 1.1670, from 1.3335 to 4.1616, from 10.026 to 99.777μg/mL and from 9.3728 to 76.517μg/mL, respectively. Resistance ratios of 66.7 % strains to riadimefon and 41.7% strains to propiconazole were more than 10, and they had higher resistant level. Meanwhile, the resistance ratios of some strains to difenoconazole, myclobutanil, tebuconazole and diniconazole were more than 10, respectively. There was some resistance risk in F. o. f. sp. fragariae to trizoles fungicides. The toxicity of tebuconazole and diniconazole to F. o. f. sp. Fragariae were high, they can be used instead of carbendaizm to control the disease.2. The triadimefon-resistant strains ZYK of wild-type (ZY001) were generated in the laboratory. The EC50 values of ZYK was 14.662μg/mL.The resistance ratio was 16.60 fold. The EC50 values of the wild-resistance TA002 was 162.81μg/mL. The resistance factor was 184.36. After 8 successive incubated on the medium without fungicide, the resistant strains ZYK could maintain their resistance. The EC50 value of wild resistant strains (TA002) had been decreased.3. The cross-resistance of induced resistant strain (ZYK) between triadimefon and other fungicides showed that: The resistant strains in F. o. f. sp. fragariae had cross-resistance to tebuconazole, diniconazole , difenoconazole, propiconazole and myclobutanil; and had no cross-resistance to carbendaizm, thiophanate-methyl and hymexazol, while ad negative cross-resistance to thiram.4. Triadimefon might damage the membrane of F. o. f. sp.fragariae. The membrane permeability of the sensitive strain ZY001 increased after treatment with triadimefon. The duced resistant strain ZYK and field resistant strain TA002 had stronger ability to adapt to triadimefon resulting in smaller membrane damage after triadimefon treatment, which decreased when triadimefon concentration increased, than the sensitive strain ZY001 had.5. The activity of phenylalanine ammonia lyase (PAL) and peroxidase (POD) on resistant strains and sensitive strain were studied after treated with triadimefon. The result showed that the activity of two enzymes was correlated with the sensitivity of F. o. f. sp. fragariae to triadimefon. After treated with triadimefon the activity of PAL isoenzymes firstly increased, at 3h, the activity of PAL isoenzymes of TA002 was highest after treated with 25μg/mL of triadimefon, the activity of TA002, ZYK and ZY001 was 613, 593 and 409 U/g·h, respectively. After treated with triadimefon in 24 h, the activity of POD isoenzymes of all strains was rose continuously, but the activity of POD isoenzymes of triadimefon-resistant strains were higher clearly than that of the sensitive strain, and the activity of POD isoenzymes of TA002 was highest. After 24h treated with 25μg/mL of triadimefon, the activity of POD isoenzymes of TA002, ZYK and ZY001 was 32.05, 22.54, 29.98 and 18.86 U/g·min, respectively.6. In order to study the changes of physiological fitness between the triadimefon-resistant strains and sensitive strain of F. o. f. sp. fragariae, the effect of different carbon source, nitrogen source, pH values, temperature values and lights were measured. The results showed that, the sensitive strain had higher growth rate than resistant strains.The sensitive strain ZY001 had higher pathogenicity than ZYK.The difference of growth speed was no evidence among these three strains in different carbon source. In the different nitrogen source, all the strains could utilize nitrites more effectively, but could not utilize (NH4)2SO4 and (NH4)2Cl. All the strains grew faster at 25 and 28℃, grew slower at 5 and 35℃. In the same temperature, the diameter of the mycelial colonies for ZYK was relatively bigger than that for ZY001.All the strains grew faster in 6, 7, 8, 9 of pH values, but when pH≥9 the colonies of three strains were thin, while there were no difference between three strains in acid and neutral conditions. The sensitive and resistant strains showed little differences in inhibition of light. |
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