Etiology Of Leaf Mold Of Paeonia Veitchii And The Disease Control

Paeonia veitchii Lynch is a perennial herb of ranunculaceae,which is distributed in northwest,northeast and North China.It is used as root and has high medicinal value and economic value.With the development and utilization of Paeonia veitchii,the demand for it is increasing,and the resources are gradually decreasing,which is diffi cult to meet the market demand.In order to protect wild resources and maintain the stable development of ecological balance,artificial nursery cultivation was carried out in Shenyang,Qingyuan,Benxi and Changtu of Liaoning Province.In the process of cultivation of Paeonia veitchii,the disease of Paeonia veitchii has become increasingly prominent,in which leaf mold is the most serious disease of the crop,which harms leaves and wilts it and inhibits plant growth.so far,there are few reports on this disease at home and abroad.In this paper,the occurrence and damage,pathogen identification,biological characteristics,activity of cell wall degrading enzymes and indoor chemical screening of the disease were studied systematically,which provided a theoretical basis for field identification and control of leaf mildew of Paeonia veitchii.1.Field investigation and pathogen Identification of Paeonia veitchii in Liaoning Province.In order to clarify the types and occurrence of main diseases of Paeonia veitchii in Liaoning Province,a systematic investigation was carried out in seven main planting areas of Paeonia veitchii,including Shenyang,Qingyuan and Changtu,from 2018 to 2020.There are five main diseases that harm the production of Paeonia veitchii in Liaoning Province.Through symptom observation,culture characteristics,morphological identification,molecular identification,specific primer detection and pathogenicity determination.The pathogens of the five diseases were identified as Cladosporium paeoniae,Cercospora brunkii,Erysiphe paeoniae,Colletotrichum coccodes and Fusarium oxysporum.Leaf mildew of Paeonia veitchii mostly occurred in early June and the peak period from mid-late August to September.The disease is widely distributed and seriously harmed,and is distributed in all the investigated planting areas.Among them,the disease is more serious in Qingyuan area,the disease index can reach more than 50%,the rate of diseased plants is about 74.5%to 100%,and the rate of diseased leaves is about 43.2%to 95.1%.The harm is extremely serious and spreads quickly,which can lead to the death of plants in batches.Erysiphe paeoniae powdery mildew is mainly distributed in Qingyuan,Shenyang,Kuandian and Xifeng,where the disease is relatively serious in Shenyang,with a diseased plant rate of about 34.5%to 56.1%and a diseased leaf rate of about 51.1%to 71.5%.Colletotrichum coccodes only occurred in Fushun Qingyuan and Shenyang,and the disease was more serious in Qingyuan.The rate of diseased plants was about 64.9%,and the rate of diseased leaves was about 53.2%and 75.1%.The anthracnose of Paeonia lactiflora is mainly distributed in Benxi,Shenyang and Faku,in which the disease is relatively serious in Benxi area,with a diseased plant rate of 32.9%and a diseased leaf rate of 55.1%.Root rot is mainly distributed in Shenyang and Faku,and the rate of diseased plants is relatively low,among which the incidence of diseased plants in Faku area is relatively serious,and the rate of diseased plants is about 12.7%～23.5%.The morbidity in Shenyang area is less than 5%,but the mortality rate of diseased plants is high,all reaching more than 90%.2.Studies on the Biological characteristics of leaf mildew of Paeonia veitchii.The study on the biological characteristics showed that the leaf mold could grow at 10～30℃,the optimum temperature was 25℃,the mycelium growth rate was 1.03 mm/d,the p H value was3～10,the optimum p H was 7,the mycelium growth rate was 1.73 mm/d,the optimum light condition was 24 hours light,the mycelium growth rate was 1.03 mm/d,and the optimum medium for mycelium growth was V8 medium,the average growth rate was 2.90mm/d.Galactose and glycine are the most suitable carbon and nitrogen sources for mycelial growth,and the mycelial growth rates are 2.00 mm/d and 1.84mm/d,respectively.Conidia can be produced at 10～35℃,the optimum temperature for spore production is 25℃,and the conidia production is 9.7×10⁶/plate.The conidia can be produced in p H was 4～10,and the maximum spore production is 6.5×10⁷/plate in p H7.The light condition of 24 hours is favorable for the production of conidia,which is 5.7×10⁷/plate.V8 medium is the most suitable medium for spore production,and the spore yield is 8.5×10⁷/plate.The conidia began to germinate at 6 h,and the germination rate reached 94.64%at 24 h.Conidia can germinate at 5～35℃,the optimum germination temperature is 25℃,and the germination rate is 72.32%.The most suitable carbon and nitrogen sources for germination are peptone and maltose,and the germination rates are 74.11%and 86.67%,respectively.Conidia can germinate under the condition of continuous darkness,and the germination rate is 91.67%.The optimum p H is 7and the germination rate is 79.11%.The temperature leading to the death of mycelium was57℃,and that of conidia was 59℃.3.Study on Cell Wall degrading enzyme and its activity of leaf mildew of Paeonia veitchii.Cell wall degrading enzyme is an important virulence factor of plant pathogenic fungi and plays an important role in the process of plaque expansion.Leaf mold of Paeonia lactiflora can produce PG,PMG,PGTE,PGTE,Cx and Ex enzymes,but the occurrence conditions are significantly different.The activity of PMG in Pectinase was determined at the spot after inoculation for different days.The results showed that the activity of Pectinase in Pectinase was the highest on the 16th day of inoculation,which was about 43.52 U/mg,while the activity of cellulase EG and Cx was relatively low.The enzyme production conditions of leaf mold were studied.The results showed that the optimum temperature for enzyme production was 25℃,in which the activity of PMG was the highest,about 2166.02 U/m L;the optimum culture time was 20 days,and the activity was about 1079.91 U/m L;24 hours of continuous concussion was beneficial to the production of CWDEs;24 hours of darkness contributed to the production of CWDEs,and the activities of PMG enzyme and PG enzyme were higher,and the activity of PMG enzyme was the highest in the condition of continuous darkness,which was about 1827.78 U/m L.The optimum enzyme production of PMG is p H 7,the activity is about 3793.638 U/m L,the most suitable nitrogen source is peptone,and the enzyme activity is about 6777.01 U/m L.The most suitable carbon source for enzyme production is sucrose and its activity is about 3028.18U/m L.By inoculating healthy leaves with Pectinase and cellulase,brown spots could be formed in the leaves of Paeonia veitchii.With the expansion of the disease spots,the disease spots of the leaves treated with Pectinase were larger than those treated with cellulase.4.Iscreening of insecticides for leaf mildew of Paeonia veitchii.The results of virulence test showed that 8 kinds of fungicides had different inhibitory effects on mycelial growth and conidia germination of Paeonia veitchii.Two kinds of fungicides with good control effect were selected,which were 400 g/L flusilazole and 50%carbendazim.Among them,400 g/L flusilazole had the strongest inhibitory effect on mycelium,the EC₅₀ value was1.801 mg/L,and the second 50%carbendazim,EC₅₀ value was 2.76 mg/L.The better inhibitory effect on spore germination was 80%mancozeb,400 g/L flusilazole,25%pyrazolyl and 50%carbendazim,and the best inhibitory effect was 25%pyrazolyl.The bacteriostatic rate of other fungicides can reach more than 80%.Combined with the epidemic law of the disease,the rational application method was planned,which laid a theoretical basis for the effective control of red leaf mildew.