Study On The Resistance Risk Of Phytophthora Parasitica Var.nicotianae To Dimethomorph

The purpose of this paper is to evaluate the risk of resistance about Phytophthora parasitica var. nicotianae to dimethomorph. The inhibitory effect of dimethomorph on 40 strains of Phytophthora parasitica var. nicotianae, which isolated from Shandong, Yunnan and Guizhou province, were determined by using mycelium growth rate method. The dimethomorph-resistant strains of wild-type(ZC001) of Phytophthora parasitica var. nicotianae were selected on medium with the dimethomorph and generated by ultra-violet. The resistance developing of Phytophthora parasitica var. nicotianae to dimethomorph and also the cross-resistance of each resistant strain were carried out.Then the difference on some biological characters such as the growth rate,dry weight of the myceliuma and pathogenicity were studied.The effect of pH,temperature and irradiate on sensitive and resistant strains were also studied.At last the resistance mechanism was studied.And the risk of resistance about Phytophthora parasitica var. nicotianae to dimethomorph was evaluate. The results could be summaried as follows:1 EC₅₀ values of 40 strains were ranged from 0.3376 to 9.5594μg/mL, the inhibitory factors were ranged from 1.05 to 29.73,compared with the sensitive strain EC₅₀ value. There were 27 dimethomorph-sensitive strains and 7 middling dimethomorph-resistant strains and 6 hignt dimethomorph-resistant strains. The EC₅₀ value of wild resistant strains had been fallen after successive incubation on the free-fungicide medium. Dimethomorph could evidently inhibit the formation of sporangia.The inhibitory rates against the sporangia formation of Phytophthora parasitica var. nicotianae was 100% by 8.0μg/mL dimethomorph.The resistance risk of Phytophthora parasitica var. nicotianae to dimethomorph was proved by testing on inhibitory activity of mycelial growth of the sub-culture fungus.2 The dimethomorph-resistant strains KX1 and KX2 of wild-type(ZC001) were generated in the laboratory. The EC₅₀ values of KX1 was 8.7024μg/mL.The resistance factors was 25.78 fold. The EC₅₀ values of KX2 was 3.9923μg/mL.The resistance factors was11.8 fold. The EC₅₀ values of the wild-resistance FX001 was 9.5594μg/mL. The resistance factors was 29.73.After 8 successive incubation on the free-fungicide medium, the resistant strains KX1 and KX2 could maintain their resistance. The EC₅₀ value of wild resistant strains (FX001)had been decreased.3 The cross-resistance of resistant strain between dimethomorph and other fungcids shew that: The cross-resistance was not in existence between dimethomorph and metalaxyl, mancozeb,chlorothalonil, cymoxanil, fosetyl-al, propamocarb.The EC₅₀ values of metalaxyl,mancozeb,chlorothalonil, cymoxanil,and fosetyl-al for ZC001 were 0.3376μg/mL, 0.1877μg/mL, 1.988μg/mL,7.6061μg/mL,18.108μg/mL and 91.733μg/mL. The inhibitory effects of metalaxyl and dimethomorph were better than other fungicides. The inhibition of propamocarb against mycelium of P. parasitica var. nicotianae was not well.The result is that propamocarb coulde be used after imbibing by the plant. The EC₅₀ value of wild resistant strains (FX001) had been decreased from 9.5594μg/mL to 6.0246μg/mL.4 In order to study the changes of physiological fitness between the dimethomorph-resistant strains and dimethomorph-sensitive strain of P. parasitica var. nicotianae, the effect of different pH values, temperature values and irradiate values was mensurated. The results showed that, the sensitive strain had higher growth rate and dry weight than resistant strains.The resistant strains FX001 had higher pathogenicity than other strains. All the strains grew faste in 6, 7, 8, 9of pH values, but grew slowe in 4 and 11 of pH values, didn't grow in12of pH values . All the strains grew faste at 28 and 32℃, grew slowe at 16 and 36℃. In the same temperature, the diameter of the mycelial colonies for ZC001and FX001 were relatively bigger than that for KX1, KX2, but there were no difference among KX1, KX2 for the diameter of the mycelial colonies. The sensitive and resistant strains shew little differences in inhibition of irradiate.5 The activity of phenylalanine ammonia lyase (PAL) and peroxidase (POD) on resitant strains and sensitive strain were studied after treated with dimethomorph. The result showed that the activity of two enzymes was correlated with the sensitive of P. parasitica var. nicotianae to dimethomorph. After treated with dimethomorph the activity of PAL isoenzymes firstly increased, at 6h, the activity of PAL isoenzymes of FX001 was highest after treated with 25μg/mL of dimethomorph, the activity of FX001, KX1, KX2 and ZC001 was604, 598,564and 504U/g·h, respectively.After treated with dimethomorph in 24 h, the activity of POD isoenzymes of all strains was rose continuously, but the activity of POD isoenzymes of dimethomorph-resistant strains was higher clearly than that of sensitive strain, the activity of POD isoenzymes of KX1 was highest. At 24 h, the activity of POD isoenzymes of KX1, KX2, FX001 and ZC001 was 42.98,23.61,29.98 and19.64U/g·min, respectively after treated with 25μg/mL of dimethomorph.The result of electrophoretic patterns of soluble proteins and esterases isoenzymes showed that the number and quantity of patterns have clear difference between the resistant strains and sensitive strain.