Monitoring the infection of powdery mildew pathogen on strawberry leaves by ATR‐IR technique

Powdery mildew is one of the most common fungal diseases in plants. The disease mainly occurs in leaves, fruits, and petioles. As infection at an early stage cannot be observed with the naked eye, it causes severe economic losses to global agriculture. Here, we used attenuated total reflection-infrared spectroscopy (ATR-IR) to identify the stage of powdery mildew infection in strawberry leaves. For naturally diseased strawberry leaves, the ATR-IR spectra on the abaxial surface had an intense peak at 1690 cm(-1), showing gradually increased intensity from early-to-late stages of infection. This peak was attributed to the acetyl and carboxyl C=O stretching vibrations of the pathogen. However, the spectra of the abaxial surface did not demonstrate a comparable change in 1690 cm(-1) peak. When strawberry leaves were inoculated with powdery mildew, ATR-IR successfully identified the stages of this anthropogenic infection. Moreover, the peak area ratio of 1690/2920 cm(-1) on the abaxial surface of strawberry leaves was extracted to quantitatively evaluate the stages of infection, using the fitting curve equation of y = 0.0015x(2)-0.0014x-0.0021 (R-2 = .9721). This study indicated potential application of ATR-IR in monitoring fungal infections in plants. In particular, the stages of infection can be quickly and accurately monitored using the ATR-IR technique.