Effects Of Tea Blister Blight On Leaf Morphology,Physiological Indices And Quality Components Of Tea Plant

Tea plant [Camellia sinensis(L.)O.Kuntze] is a perennial economic crop.Its young leaves are processed into “tea”,which contains many substances beneficial to human health,such as tea polyphenols,free amino acids,caffeine,sugars.However,the quality and yield of tea are affected by a variety of tea diseases,which restricts the normal development of tea industry.Blister blight,also known as leaf swelling,is an obligate fungal disease caused by Exobasidium vexans Massee.The disease mainly damages the young succulent leaves and stems of tea plants,often causes browning,curling and leaf tissue necrosis of tea leaves,and seriously affects the economic value of tea.This study takes the tea area in southern Shaanxi as the main research object to investigate and analyze the prevalence of blister blight.To study the effects of Exobasidium vexans invasion on the changes of tea leaf morphology,physiological and biochemical indexes and tea quality components in the year,and on the quality components of tea new shoots in the next year,in order to provide a scientific basis for prevention and control of blister blight.The interaction between tea plant and pathogens and lay a foundation for the prevention and control of tea blister blight diseases.The main results as follows:1.In this study,the blister blight is the main leaf disease of most tea gardens in this area,which seriously affects the economic value of local tea.Among them,the incidence of blister blight in Xiakou Town,Luojiaba town and Sidu town of Xixiang County in southern Shaanxi is extremely serious,with an average incidence rate of more than 95%.The incidence rate of Hanyuan town and Gaozhaizi Town,Chenggu mountain tea garden and Yanbin town of Yanba town in Ningqiang County is 72.4%-92.6%.In Fuchuan Town,Mian County in the central part of Southern Shaanxi,the disease is more serious,and sporadic findings have been found in other tea gardens;There is no prevalence of blister blight in most areas of southern and Northern Shaanxi.The onset period of blister blight in southern Shaanxi tea area was early May,and the outbreak period was from June to July and September to October.Tea plantations with large-scale planting groups and elderly tea plants(> 40 years)in this tea area are more vulnerable to Exobasidium vexans.Blister blight is mostly prevalent in tea plantations at an altitude of 510 m-1000 m,especially in tea plantations with extensive management.2.The infection of blister blight seriously affects the morphology and internal structure of tea leaves,reduces the availability and photosynthetic efficiency of fresh leaves,and reduces the yield of tea.Evans blue and trypan blue staining were used to observe the cellviability and allergic necrosis reaction of tea leaves.It was found that the allergic necrosis of tea cells in the diseased area decreased the cell viability,which reduced the availability of fresh tea leaves and the utilization rate of light energy.Shiff iodate and toluidine blue staining were used to observe the invasion mode of Exobasidium vexans and the changes of cell structure of tea leaves in different stages of disease.It was found that Exobasidium vexans invaded tea plants from the joint of lower epidermal cells of tea leaves,occupied sponge tissue cells and cell gaps,absorbed sponge tissue cell nutrients and destroyed cell structure.The effects of Exobasidium vexans on the vitality and structure of sponge tissue cells were further observed by transmission electron microscope.The results showed that Exobasidium vexans could overflow cell fluid,reduce organelles such as chloroplast and mitochondria,and reduce the photosynthesis of tea plants by destroying the vacuolar membrane of sponge tissue cells.The mature basidiophores cluster and break through the lower epidermal cells of leaves to form sporophore for the next round of transmission and infection.3.Tea plants improve their resistance to blister blight by regulating the changes of defense enzyme activity and stress resistant substances in vivo.It was found that in the early stage of Exobasidium vexans invasion,the activities of superoxide dismutase and peroxidase increased,the activities of phenylalanine ammonia lyase and catalase decreased,the content of malondialdehyde and proline increased,and the activities of four defense enzymes and the contents of malondialdehyde and proline decreased in the later stage of infection.4.The invasion of Exobasidium vexans changes the content of quality components in fresh tea leaves,which seriously affects the quality of tea.The results showed that the total amount of tea polyphenols decreased,the contents of catechin EGCG,ECG,C and GC decreased,the content of CG increased,the total amount of free amino acids decreased,the content of soluble protein increased,and the contents of bacteriostatic caffeine and volatile substances closely related to defense(E)-2-hexenal,linalool,methyl salicylate and neophytadiene increased.5.In order to further explore the effect of blister blight stress on the formation of tea quality,the quality components of healthy and diseased tea shoots in the second year were determined.It was found that the contents of tea polyphenols,catechins and free amino acids that formed astringency,bitterness and fresh sweetness decreased,and the content of caffeine that formed bitterness increased;The precursors of(Z)-3-hexenal and(E)-2-hexenal that produce bad aroma green leaf alcohol increased,while the contents of volatile substances such as linalool,linalool oxide and neophydiene that produce flower fragrance decreased.In conclusion,this study takes the blister blight in southern Shaanxi as the starting point,studies the invasion mode of Exobasidium vexans,the changes of tea leaf morphology,physiological and biochemical indexes and tea quality components under the stress of blister blight,and the differences of main components of tea taste and aroma formation in the new shoots of the next year,so as to reveal the influence of blister blight on the growth and development of tea plants and the formation of tea quality from the outside to the inside,In order to lay a theoretical foundation for tea plants to resist blister blight.