| Tobacco black shank was the most common devastating soil borne fungal diseases and caused great losses to the farmers and tobacco industry.How to effectively prevent tobacco black shank has always been the hotspot and focus of research in tobacco production.It was great significance to understand the characteristics of adsorption and migration of zoospores in soil,build appropriate mathematical models to predict its migration behavior,and investigate the main influencing factors affecting the infection of zoospores for improving the prevention system of tobacco black shank and achieving“green plant protection”and“green planting”of tobacco.Therefore,this study used tobacco black shank labeled with GFP as test organism,through indoor equilibrium adsorption experiments and soil column migration experiments to investigate the effects of soils with different utilization patterns?red soil paddy soil and red soil dry soil?and soil added woody peat on zoospores'adsorption and migration behavior,and through laboratory experiments to study the effects of root injury,drought stress and nitrogen form on the zoospore-infected tobacco.The results are as follows:?1?The adsorption and migration of P.nicotianae zoospores in soil were affected by soil utilization patterns.The adsorption isotherm line of P.nicotianae zoospores both in reddish paddy soil and in red soil upland agreed with the Freundich adsorption equilibrium model.Zoospores'isothermal equilibrium adsorption constants of K was 1.0836 mL?g-1 in the red paddy soil,and one's of K was 1.5125 mL?g-1 in red soil upland.The adsorption of zoospores in reddish paddy soil achieved a state of equilibrium in 40 min,and the reversible adsorption constant(Katt)and reversible desorption constant(Kdet)were 1.7147×10-11 s-1 and5.3639×10-22 s-1,respectively;in red soil upland achieved a state of equilibrium in 50 min,and the reversible adsorption constant(Katt)and reversible desorption constant(Kdet)were6.7439×10-2s-11 and 2.0211×10-22 s-1,respectively.The vertical migration of P.nicotianae zoospores was hindered by both reddish paddy soil and red soil upland,which makes that the zoospores mainly stayed in the soil column that ranged from 05 cm.In addition,the redistribution of the zoospores appeared in the unsaturated soil increased the downward migration of the zoospores.?2?The adsorption capacity of soil to P.nicotianae zoospores was enhanced after added woody peat.When the reddish paddy soil and red soil upland were applied to woody peat,in both of them the Zoospores'equilibrium adsorption constants of K was increased,as well as the Zoospores'downward migration in the soil column breakthrough experiment was increased.In red paddy added with woody peat,zoospores'isothermal equilibrium adsorption constants of K was 1.6058 mL?g-1;the adsorption of zoospores basically achieved a state of equilibrium in 40 min,and the reversible adsorption constant(Katt)and reversible desorption constant(Kdet)were 1.1851×10-1s-1 and 2.5015×10-22 s-1,respectively.In red soil upland added with woody peat,zoospores'isothermal equilibrium adsorption constants of K was 2.2156mL?g-1;the adsorption of zoospores basically achieved a state of equilibrium in40 min,and the reversible adsorption constant(Katt)and reversible desorption constant(Kdet)were 8.011×10-22 s-1 and 1.580×10-22 s-1,respectively.?3?The incidence,the disease index and the protective enzyme of tobacco seedlings were remarkably affected by injured root degree and P.nicotianae zoospores'concentration.The activity of SOD?POD?CAT?PAL and the content of MDA in leaves,as well as the incidence and the disease index of xiaohuangjin 1025?susceptible variety?and K326?medium resistant variety?were all increased with the increase of injured root degree and P.nicotianae zoospores'concentration.Under the same condition,both the SOD?POD?CAT and PAL activity and their increasing speed in K326 leaves were higher than that in xiaohuangjin 1025,while the incidence and disease index were just the opposite.In the same concentration of zoospores solution,the antioxidant enzyme activity of leaves treated with injured root increased faster than ones treated with non-injured root on the whole.?4?Moderate drought stress was conducive to enhance the resistance of tobacco seedlings.With the aggravation of drought stress,in all treated tobacco seedlings the disease index and the incidence were decreased on the whole,and the activity of SOD?CAT?POD?PAL and the content of proline and lignin were all increased,while the growth rate decreased gradually.Under mild and moderate drought stress,both the disease index and the incidence of tobacco seedlings were the highest in treatment which was inoculated by P.nicotianae zoospores before and after drought stress?T3 treatment?,and ones were the lowest in treatment which was inoculated by P.nicotianae zoospores after drought stress?T2treatment?.Under severe drought stress,both the disease index and the incidence of tobacco seedlings were the lowest in treatment which was inoculated by P.nicotianae zoospores before drought stress?T1 treatment?,and ones were the highest T3 treatment.Normal cultivation to moderate drought stress,the disease index and the incidence of tobacco black shank of T2 treatment were lower than ones of T1 treatment,and the gaps of the disease index and the incidence between the two treatment was gradually increased,further more the disease index increased more significantly.?5?Black shank zoospores'germination and infection was affected by nitrogen forms.The appropriate proportion of nitrate nitrogen?NO-N?and ammonium nitrogen?NH-N?helps to improve the disease resistance of tobacco seedlings,to reduce the disease index and the incidence of tobacco black shank.However,the high concentration of NH-N presents a toxic effect on the growth and development of the tobacco seedling root.The germination of P.nicotianae zoospore was accelerated by nitrate,ammonium and their mixed solution,while there was no significant difference in the final germination rate of zoospores between all treatments.With the increase of NH-N concentration in the solution,the root morphology was changed,and the root biomass was reduced,as well as the root growth and development were inhibited,while both the incidence and the disease index of tobacco seedlings were decreased significantly,the content of lignin,cellulose and MDA,as well as the activity of antioxidant protective enzyme were increased significantly in tobacco seedlings roots.Proteomics research showed that 40 protein in roots treated respective by NO-N to NH-N of 10:0,5:5 and 0:10 were differentially expressed,and 36 of 40 were successfully identified,which were involved in energy production,signal transduction,cell defense related pathways.Based on the results of this study,it is suggested that 05 cm soil layer is used as a key point in the prevention of tobacco black shank and the application of biochar in soil to reduce the spread of zoospores in tobacco fields.In addition,it is also recommended to improve the resistance of tobacco seedlings through appropriate drought stress and application of nitrogen fertilizers with NO-N to NH-N of 7:35:5,avoid damage to the roots during the nursery and transplanting farming operations,and try to develop a new type of nursery method in some tobacco fields. |
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