Effects Of Exogenous 6-BA And Melatonin On The Physiological Characteristics Of Bluberry Under Drought Stress

The blueberry is an emerging small berry species with high economic value and great potential for exploitation.The blueberry fruit is blue or red in colour and the blue fruit type is commonly known as Blueberry.Drought has now become the most significant factor affecting crop yield reduction.In this study,we investigated the effects of exogenous 6-BA and melatonin on the mitigation of drought stress in blueberry"Northland"to provide a scientific basis for the use of blueberry and other fruit trees in drought-resistant cultivation.In this experiment,the two-year old semi-highbush blueberry’Northland’was used as the test material,with four treatments:normal irrigation（CK）,mild stress（D1）,moderate stress（D2）and severe stress（D3）.The study applied exogenous sprays of 6-BA at 50、100、150 and 200mg/L and melatonin at 100、200、300 and 400μmol/L to D1（10 d water cut-off,55-60%of maximum field water content）,D2（15 d water cut-off,35%-40%of maximum field water content）and D3（20 d water cut-off,20%-25%of maximum field water content）respectively.and 100,200,300 and 400μmol/L of melatonin.The growth indexes,physiological indexes and leaf anatomy of blueberry leaves were measured,and the effects of drought treatment and exogenous 6-BA and exogenous melatonin on the drought resistance of blueberry were investigated by correlation analysis and principal component analysis,respectively.The results of this study were as follows:1.With the increase of drought stress,the growth index,relative leaf water content and chlorophyll content of blueberry showed a decreasing trend,the relative conductivity,Pro and MDA content showed an increasing trend,the SS and SP content and SOD an d CAT activities showed an increasing trend and then a decreasing trend.With increasin g drought stress,leaf thickness,upper epidermal thickness,lower epidermal thickness,fe nestrated thin-walled tissue thickness and spongy thin-walled tissue thickness showed a d ecreasing trend.With the increase of drought stress,Pn,Tr,Gs,Fv/F₀ and Fv/Fm of blu eberry leaves showed a decreasing trend and Ci showed an increasing trend,with signifi cant differences（P<0.05）starting from the D2 period.2.Under drought treatment,blueberry plants were able to cope with the drought envi ronment by increasing antioxidant enzyme activity and osmoregulatory substances on thei r own.A principal component analysis was conducted on 23 indicators of blueberry afte r drought treatment,and sponge thin-walled tissue thickness,Fv/Fm,Pro content,Ci,lea f thickness,Tr,Chla content,SOD activity,SS content and CAT activity were selected a s indicators to evaluate the ability of blueberry to resist drought stress.3.Exogenous 6-BA and melatonin at appropriate concentrations effectively reduced th e decrease in relative water content and degradation of chlorophyll content of blueberry leaves under drought stress.In terms of physiological indexes,exogenous 6-BA and mel atonin at appropriate concentrations reduced the MDA content and relative conductivity o f blueberry leaves under drought stress,while increasing Pro,SS,SP content and SOD and CAT activities.Exogenous 6-BA and melatonin increased the thickness of blueberry leaves,upper epidermal thickness,lower epidermal thickness,fenestrated thin-walled tissu e thickness and spongy thin-walled tissue thickness under drought stress.For photosynthe tic characteristics and chlorophyll fluorescence,the exogenous 6-BA and melatonin at ap propriate concentrations increased Pn,Tr,Gs,Fv/F₀ and Fv/Fm of blueberry leaves and decreased Ci value of blueberry leaves.The combined scores by principal component an alysis showed that 6-BA3>MT3>MT2>6-BA4>MT4>MT1>6-BA1>D1 und er D1 treatment,6-BA3>MT2>MT3>6-BA4>MT4>6-BA2>MT1>6-BA1>D2 under D2 treatment,MT3>6-BA4>MT4>MT2>6-BA1>D2 under D3 treat ment,and MT3>6-BA4>MT4>MT2>6-BA3>6-BA2>MT1>6-BA1>D3.4.Under drought treatment,exogenous 6-BA and melatonin can change leaf structure and photosynthetic capacity,increase antioxidant enzyme activity and osmoregulatory su bstances to enhance the drought resistance of blueberry.150 mg/L 6-BA under D1 and D2 treatment and 300μmol/L melatonin under D3 treatment are the most effective.