Screening And Safety Evaluation Of Fungicides For Controlling Main Diseases Of Crisp Plum(Prunus Salicina)

Cultivation and adaptability of Plum were extremely wide,and has become one of the main fruit industries to help poverty-alleviation in Guizhou.Because the fruit is green,crisp,sweet and popular with the masses,crisp plum has been the main cultivated varieties of Guizhou local plum.With the continuous expansion of the planting area,the widespread occurrence and serious damage of plum diseases have restricted the sustainable development of the plum industry.However,there were few systematic studies on plum diseases at present.In this paper,in order to provide a certain reference for the green prevention and control of crisp plum diseases,the occurrence of plum tree diseases were investigated.And the pathogen identification,biological characteristics analysis and fungicides virulence determination of three diseases of crisp plum,brown rot,new fruit spot and leaf spot were carried out.In addition,field trials for controlling leaf spot and brown rot and fruit safety evaluation were tested.The main research results were as follows:1.The occurrence of plum tree disease was investigated There are 9 common fungal diseases of plum trees in Guizhou,among which brown rot is the most serious disease affecting plum fruit,and it occurs in all varieties in rainy season.Red spot disease occurred more seriously on‘crisp red’plum and‘rose’plum,but occurred locally in other varieties.Leaf spot mainly occurred on‘April’plum and‘honey sweet’plum leaves,sporadically occurred on crisp red plum.Fruit spot is harmful to fruits of‘April’plum and‘honey sweet’plum,which showing deformities,wilting,concave lesions,and then blackening and rotting.Bacterial perforation disease mainly occurred on branches and leaves and was serious in some planting areas.In addition,gummosis,bag fruit disease,virus disease and septobasidium pedicellatum are equally harmful,which occur locally in the field and are less harmful.2.Pathogen identification and biological characteristics analysis of three kinds of diseases in crisp plum were carried out.Three fungal diseases were collected for isolation and purification,pathogenicity determination,morphological identification,molecular biological identification and phylogenetic analysis.It was confirmed that the pathogen of American-Australian type brown rot was the Monilinia fructicola,and the pathogen of the new fruit spot disease was Fusarium fujikuroi,and the pathogen of new leaf spot disease was Alternaria alternata.First of all,the optimum temperature for growth of American-Australian type brown rot fungus（M.fructicola HF1）was 25℃,the optimum PH was 7,and the utilization rate was the highest when glucose was the carbon source and peptone was the nitrogen source.The most suitable light condition for the growth of the strain was light-dark alternation（12:12）.Second,the new fruit spot disease（F.fujikuroi HJGF1）grows at an optimum temperature of25℃and an optimum PH of 7,with the highest utilization rate when glucose and sodium nitrate were used as carbon and nitrogen sources,respectively,the most suitable light condition for the growth of the hypha was all black（24 h）.In the end,the optimum temperature for growth of Alternaria alternata（A.alternata HJHB1022）was 25℃,the optimum pH was 7,and when maltose was used as carbon source,peptone was the utilization rate of nitrogen source was the highest,and the effect of different light treatments on the growth of the pathogenic fungus hyphae was not significant.3.The virulence of fungicides to the three pathogens was determined by the mycelial growth rate method.The fungicides that had strong inhibitory effect on the mycelium growth of F.fujikuroi HJGF1 were eugenol,penthiopyrad,prothioconazole,azoxystrobin and cyprodinil,which the EC₅₀ values were 2.1821 mg/L and 4.1074 mg/L,4.8704 mg/L,5.2313 mg/L and 6.2818 mg/L,respectively.eugenol and penthiopyrad had strong inhibitory effects on the mycelium growth of A.alternata HJHB1022,with EC₅₀ of 0.8642 mg/L and 4.4939 mg/L,respectively.In addition,Eugenol,prothioconazole,penthiopyrad,berberine,cyprodinil,fenethanil and azoxystrobin all had strong inhibitory effects on the hyphae growth of M.fructicola HF1,and their EC₅₀ values were 0.1295 mg/L,0.3015 mg/L,1.0395 mg/L,1.8581mg/L,2.2315 mg/L,4.4026 mg/L and 5.0843 mg/L,respectively.At the same time,two kinds of formula combinations with synergism on the bacteria were screened out,namely,prothiazole and pyrimethanil,pyrimethanil and pyrimethanil,respectively.The formulas ratio were 1:1,and the EC₅₀ values were 0.1140 mg/L and 1.1347 mg/L,respectively.4.According to the virulence of the fungicides,field trials of different fungicides against leaf spot and brown rot were tested.The results showed that the spray treatment with 20%pyrazinamide suspension 2000 diluted multiples liquid and 50%cyclopyrimidine water dispersive granule 800 times had better control effect on‘honey sweet’plum leaf spot,which the control effect was 75.11%and 73.67%and were significantly different from that of other three fungicides.The second was the treatment with 2000 diluted multiples solution of 25%azoxystrobin suspension.The spray treatment with the synergistic combination of prothioconazole and azoxystrobin（1:1）suspending agent 2000 diluted multiple liquid,penthiopyrad and azoxystrobin（1:1）suspending agent 2000 times had better control effect on the brown rot of‘Crispy red’plum,which the control effect reached 81.01%,79.33%and were significantly higher than that of single fungicide treatment.In single fungicide treatments,the treatment with 30%propanthiazole dispersible oil suspension 2000diluted multiples liquid and 20%pyrazolamide suspension solution 2000 times had better control effect,which could be used in rotation in production.Four kinds of fungicides with better control effect were selected for further determination of fruit quality.Compared with the control group,the appearance and internal quality of the fruit were significantly improved by application of fungicides.In particular,the effect was better treated with prothiazole-azoxystrobin（1:1）suspension.5.A HPLC-MS/MS analytical method was established for the determination of azoxystrobin residues in plum fruit and soil.In the range of 0.05-2.00μg/mL,a good linear relationship was found between the concentration of azoxystrobin and the peak area.The standard curve was y=38621x+874.85,the correlation coefficient was0.9969,and the retention time of pyrimethanil was 0.842 min.When the standard sample supplemental level was 0.1-5 mg/kg,the recovery rate of azoxystrobin in plum fruit and soil were 83.41%-97.22%and 85.89%-92.64%in plum fruit and soil,and the relative standard deviations were 2.35-3.02 and 2.01-5.62,respectively.In the field experiment,the residue of azoxystrobin in plum fruit and soil was 0.0601 mg/kg and0.0989 mg/kg,which did not exceed the maximum residue limit of 2 mg/kg on plum in China.