Infection Mechanism And Green Control Of Peach Shoot Blight

Peach shoot blight is a major fungal disease of peach in the main peach growing areas of southern China,which seriously threatened the development of peach industry.In order to control the disease effectively,this paper studied the infection mechanism of the pathogen Phomopsis amygdali on peach trees,including the infection process,infection conditions and pathogenic factors,and identified another two isolates of peach shoot blight.Furthermore,the green control of the disease was studied in the field.The germination process of conidia of P.amygdali was studied.The results showed that all conidia germinated at 9 h post inoculation(hpi),produced germ tubes at 9—12 hpi.Then,new hyphae were observed at 12—24 hpi and septum appeared at 30 hpi.The results on infection process of P.amygdali by scanning electron microscope indicated that the pathogen has no effect on the phloem and pith of twigs of peach,but mainly damaged the xylem vessel that delivered water and nutrients for peach trees by leading them gradually decayed and changing their arrangement though accumulating a mass of hyphae.Therefore,it might be one of the reason of canker spots and the death of the upper twigs caused by P.amygdali.The pathogenicity of P.amygdali under different environmental conditions(temperature,light,relative humidity)were studied.The results showed that the pathogenicity of amygdali was the strongest at 30?,followed at 25?.Too high or too low temperature would inhibit the pathogenicity of P.amygdali,and the inhibition effect of low temperature was greater.Then,the treatments of different lighting time were studied after inoculation of 24 hours:all light,12 h light/12 h dark,all dark,followed by a 12 h light/12 h dark cycle for 7 days.The results showed that different light treatments in the first 24 h after inoculation had no significantly difference on the pathogenicity of P.amygdali.Experiments with different relative humidity conditions indicated that high relative humidity(RH 98%)was necessary for the pathogenicity of P.amygdali,and pathogen with too low relative humidities were less pathogenic or even non-pathogenic.Whatsmore,the cell wall degrading enzymes were induced by modified Marcus medium,the polygalacturonase(PG),pectin methylgalacturonase(PMG),pectin methyl trans-eliminase(PMTE),polygalacturonic acid trans-eliminase(PGTE)and cellulase(Cx)were both found in extracellular and intracellular proteins of P.amygdali.Among them,the enzyme activities of PG and PGTE were the highest,while the enzyme activity of PMTE was relatively low.Results showed that those cell wall degrading enzymes could be secreted by P.amygdali which might decompose the cell wall of peach twig cells.Moreover,the crude toxin was extracted through induced by related medium.The results indicated that the crude toxin could cause damage to peach twigs at a certain concentration,and the symptoms of damage were consistent with those of peach shoot blight,indicating that the toxin might be one of the pathogenic factors of P.amygdali.In addition,in this study,except Phomopsis amygdali,there were two other species of Phomopsis that could also cause peach shoot blight,which were preliminarily identified as P.liquidambari and P.eres.The biological characteristics of the two pathogens were studied,it was found that their mycelial growth speed and pathogenicity were significantly higher than that of P.amygdali.The results updated and improved the pathogens of peach shoot blight,and laid a theoretical foundation for the effective control of peach shoot blight.In this paper,a field trial of green control for peach shoot blight was carried out in Yangshan,Wuxi,Jiangsu Province,which formed a green control technology model of peach shoot blight composed of agricultural control,biopesticides(zhongshengmycin and shenqinmycin)and chemical fungicides(prochloraz,carbendazim and diniconazole)mixtures control.There was no significant difference between green control and conventional chemical control in the same period and in the quality of peach fruit.However,the use of chemical fungicieds and the residues of chemical fungicides such as carbendazim in peach fruit were both significantly reduced.The economic evaluation showed that green control had obvious economic benefits with the output value increased by 8.15%compared with conventional chemical control.These measures laid a foundation for efficient and green control of peach shoot blight and sustainable development of peach industry,and also provided ideas and technical models for green control of other diseases and insect pests in peachorchards.