Infection Process Of Broomcorn Millet Smut Fungus And Host Cell Ultrastructure Obervation

Broomcorn millet(Panicum miliaceum L.)is one of the most important grain and cash crops in arid and semi-arid areas,with the characteristics of short growth period,high efficiency of water using,easy cultivate.Smut is one of the important diseases in the broomcorn millet industry,which seriously affects the yield and quality of broomcorn millet.Broomcorn millet smut is a system infection disease,pathogen in invasive broomcorn millet plant in early stage,but obvious symptoms perform in the mature period.It is impossible to identify whether the host was infected by S.destruens though physiological or appearance characteristics,in the early stage.It is of great significance for the early diagnosis,prediction and prevention of this disease that established a molecular detection system for broomcorn millet smut disease.Sporisorium destruens is abbreviated as S.destruens.It is of great significance to study the pathogenic mechanism of S.destruens,the interaction between pathogen and host,and the disease resistance mechanism of broomcorn millet plants in the future to study the colonization and infection process of Sporisorium destruen,analyze the differentiation process of healthy and diseased strains of broomcorn millet and observe the ultrastructural of infected plants.In this study,the specific primers of S.destruens were designed,and the conventional PCR detection system of S.destruens was established to provide technical support for the early detection of broomcorn millet smut.The colonization and infection of S.destruens in broomcorn millet were studied by PCR.Four typical symptoms of broomcorn millet smut were observed,and the differences of young ear differentiation process between healthy plants and disease plants were compared and analyzed,and the formation process of blackfly was clarified.The ultrastructure of the ear part of the disease broomcorn millet plant was observed.The study reached the following conclusions:(1)No positive bands were amplified from Sds-F/Sds-R except for S.destruens,indicating that the primer set was specificity for S.destruens.The amplification size of the primer sets was 465 bp.The minimum detection was 100 ng from disease plants and 10 pg from S.destruens.Observing 5 days after inoculation,we found that S.destruens infected the host by forming a formation of appressorium,the pathogen colonized bacon,hypocoel and germ sheath of the host.The colonization site of the pathogen was no limited.Among the colonized tissue sites,the number of young tissue sites was higher than that of old tissue sites.S.destruens invaded the host and grew up with the growth point,finally invaded the ear of the host,only a small amount of hyphae left in the older tissues,and it multiplied rapidly in the ear,formed teliospores and became the infection source in the next year.The smut of broomcorn millet is a systemic infection disease,the colonization site and infection site of the pathogen have no limitations.(2)There are four typical symptoms of broomcorn millet smut: blackfly,cluster leaves hedgehog head,incomplete fruiting.The characteristics of the reproductive organs of the cluster-like and hedgehog-like plants disappeared,the reproductive organs were transformed into vegetative organs--leaves.The difference of the different symptoms of broomcorn millet smut may be caused by the different developmental state of the inflorescence when S.destruens invaded.Healthy plants undergo normal ear differentiation process.In disease plants,the pathogen invaded the host ear tissue at the early stage of panicle differentiation.The ear differentiation of disease plants remained at the stage of stem system differentiation,after which the ear differentiation was no longer carried out and only the maturation of teliospores.(3)S.destruens was not observed in healthy broomcorn millet plants,and the root,stem,leaf and leaf sheath were not damaged by pathogens.In diseased plants,S.destruens in the root,stem,leaf and leaf sheath of the host,symbiosis with the host,existing as a form of biotrophic pathogens,without causing the death of the tissues in these parts.The pathogen only forms teliospores in the ear of the broomcorn millet and exists in the ear in the form of necrotic pathogen.The pathogen interacts with the broomcorn millet after invading the host,a series of changes take place in the host,the disorder host cytoplasm,cellular organelle arose,vacuolization of cells,the cell wall was degraded and finally completely dissolved.The cells degrade gradually and extensively ultimately,causing total necrosis of host ear tissue.