Freezing Injury Physiological Mechanism And Preventing Methods Of Young Loquat Fruits Under Low Temperature Stress

As a typical tropical fruit, the loquat (Eriobotrya japonica lindl) has high economic value.Because of Physiological characteristics in loquat and Climate characteristics in Southwest China,loquat fruits are easy to suffer freezing injury.Therefore,it may bring enormous economic loss.Sichuan province is one of the main planting area,however,with the increase of freezing injury in recent years,the yield of loquat reduced current annual and the fruit ranch is badly damaged. Low temperature stress is the important factor of restricting loquat yield and affecting loquat industry.Therefore,there is an important meaning in studying on physiological harmed mechanism and preventing methods.In this research,by analyzing meteorological factors,investigating freezing injury situation,determining index of freezing injury and antioxidant enzymes in young loquat fruits under low temperature stress, the effect of freezing injury in young loquat fruits by meteorological factors,the relationship between different growth degree and freezing injury in young loquat fruits and effect of physiology and biochemistry in young loquat fruits at low temperature stress had been studied on.Then the effect of covering shading nets and spraying MSOD had been studied and discussed.In order to reveal physiological and biochemical difference in different growth degree,different treatments of covering nets and different concentrations of MSOD treatments in young loquat fruits under low temperature stress and provide basis of theory and practice in cold resistance measures in young loquat fruits.The results are as follows:(1)There is great temperature difference in morning and evening,and the greatest temperature difference is 16.3℃ in winter in Shimian county.During the wintering,young loquat fruits’have weak cold resistance ability and have no cold hardening. As the consequence,the decrease and increase sharply of temperature is the main reason to cause the freezing injury.Sun day is always after frost weather,then interaction of freezing injury at night and illumination in daytime can usually induce photo inhibition phenomenon.This can aggravate the degree of freezing injury.In addition,there isn’t rainfall as long as 3 months,so dry freeze situation aggravate harm degree to young loquat fruits.(2)The seeds of young loquat fruits are more easily get freezing than the flesh,which is the main reason to cause young loquat fruits to get freezing.Different MDA content and cell membrane permeability in different development degree in young fruits under low temperature stress,however,they are decreased with the increase of development degree.The activity of SOD,CAT,APX and POD improved in different degree in the same case.Therefore,with the increase of development degree,the freezing degree of young loquat fruits are decreased. That is to say,in range of experimental treatment,the transverse diameter≥2.0cm of young loquat fruits have the lightest freezing injury.SOD,CAT,APX and POD have certain synergistic action to scavenge active oxygen during freezing injury.The rate of activity change in POD is the biggest.Therefore,POD is the key enzyme of scavenging active oxygen in young loquat fruits under low temperature stress.(3)Relative conductivity and content of MDA had significant positive correlation with index of freezing injury in young loquat fruits after covering different specifications and colors’shading nets.These treatments made different effects on inducing the activities of SOD,CAT,APX and POD, but same effects on reducing content of MDA and relative conductivity.The activity of antioxidant enzymes of CK2 have significant discrepancy with the black shading nets with shading rate of 50%,70% and 90%.The activity has the tendency of increasing at first then decreasing with the increase of shading rate of black shading nets.Moreover,the activities of SOD,CAT,APX and POD reached the maximum after covering black shading net with 70% shading rate. However, under the treatments of black and silver shading nets with shading rate of 70%,there are little discrepancy of physiological indexes in young loquat fruits,but black shading nets of 70% shading rate have better slightly effect of cold resistance than silvers’. In range of experimental treatment,black shading net of 70% shading rate has the best effect of decreasing indexes of freezing injury,cell membrane permeability,content of MAD and increasing activities of antioxidant enzymes.(4)MSOD with different concentrations (5.0mg/L、12.5mg/L、20.0mg/L) made different effects on inducing the activities of SOD,CAT,APX and POD,but they can reduce cell membrane permeability and content of MDA indicating that by activating activities of antioxidant enzymes young loquat fruits’ cold resistance will be enhanced.The activities had the tendency of increasing at first then decreasing with the concentrations of MSOD.In the three concentrations of 5.0mg/L、12.5mg/L、 20.0mg/L, the concentration of 12.5mg/L had the best effect.