Early Identification And Monitoring Of Strawberry Powdery Mildew Based On Attenuation Total Reflection Fourier Transform Infrared Spectroscopy

Strawberry is an important economic crop of Rosaceae species.Chinese strawberry industry has developed rapidly in recent years,is the largest country in the world in terms of production and planting area in China.However,powdery mildew has been an increasingly serious problem because of the high cultivation density,extensive management and airtight cultivation facilities.The rate of infected leaves was more than 45%,and the rate of infected fruits was more than 50%in greenhouse,which has a negative effect on strawberry’s products and quality.Furthermore,Powdery mildew is difficult to control because of the unconspicuous symptoms and high transmitting speed.Infrared spectroscopy technology is based on the detection of the loss of characteristic bands for a particular chemical bond after the absorption of different wavenumber range of infrared radiation.This kind of information directly relates to the biochemical composition of the sample,which can quickly reflect its structure and composition.It is a non-destructive and maneuverable identification technology.The application of spectrum in agriculture is mainly focused on hyperspectral remote sensing,while the application of infrared spectrum in strawberry is extremely lacking.In this study,the characteristics of the infrared spectrum were studied by Attenuated Total Reflection Fourier Transform Infrared（ATR-FTIR）analysis on the leaves inoculated with powdery mildew spores and those infected with powdery mildew in the field.By the qualitative and quantitative analyses of infrared spectrum data,it has been revealed that strawberry powdery mildew could be detected before symptoms appear.In order to explore the application of ATR-FTIR technology on the powdery mildew disease and provide a fast and accurate method,random sampling was carried out in five strawberry facilities in Hemu Expo Garden and Strawberry Square in Baitu Town,Jurong District.The main results are as follows:1.The leaves of the healthy strawberries were treated with the spores of powdery mildew,and the leaves of the strawberries were analyzed by ATR-FTIR.It was found that the band(1690 cm^-1)on the back of the leaves belonging to the stretching vibration of C=O of acetyl and carboxyl changed significantly,which could be used as the characteristic identification peak of the infection of strawberry powdery mildew.Moreover,the peak did not overlap or partially overlap with other infrared peaks,and was highly sensitive to the detection of the leaves without obvious spots at the initial stage of infection and on the surface.The peak area ratio of 1690/2920/cm on the back of strawberry leaves was further extracted,and the curve of fitting the infection process and characteristic peak ratio of strawberry leaves was established（Y=-0.0015x²-0.0014x-0.0021,R²=0.9743）.Thus,the specific infection stage of strawberry powdery mildew can be inferred according to the ratio of characteristic peak intensity of infrared spectrum.In order to perform field monitoring,the strawberry leaves in three stages（no white hyphae,visible white hyphae and visible massive white lesions）of powdery mildew in greenhouse were analyzed by ATR-FTIR.The results showed that the 1690 cm^-1characteristic peak could be detected sensitively on the back of leaves without white hyphae,and the 1690/2920/cm peak area ratio of strawberry leaves at each susceptible stage was consistent with the susceptible characteristics of strawberry leaves inoculated with corresponding infection days.2.The infection of powdery mildew was monitored by ATR-FTIR technique from February 7 to March 22.Five greenhouse facilities were set up in Hemu Farm Expo Garden and Strawberry Square in Baitu Town.The results showed that on March 8,when white mycelia were not observed on strawberry leaves,the characteristic peak of 1690 cm^-1appeared in the leaves of Shed 1 and Shed 2.One week later,it was observed that there were white spots of uneven size on the front and back of strawberry leaves in Shed 1 and Shed 2.On March 15,the characteristic peak of 1690cm^-1was detected when white hyphae were not observed on the strawberry leaves in shed 3,and white disfigured spots were observed on strawberry leaves in shed 3 on March 22.No characteristic peak of 1690 cm^-1was detected by ATR-FTIR technique in Shed 4 and 5,and no signs of powdery mildew were detected during the observation period（Feb.7 to Mar.22）.Our results indicate that ATR-FTIR technology can be used to detect strawberry powdery mildew in the field when no white hyphae are observed,which provides a new method for the early detection of strawberry powdery mildew.