Non-destructive estimation of weed response to bleaching herbicides by Raman spectroscopy.

The aim of our study was to evaluate the use of Raman spectroscopy for pre-diagnostic estimation of weed response to bleaching herbicides. Model plants were Chenopodium album and Abutilon theophrasti treated with mesotrione (120 g a.i. ha^-1). Raman single-point measurements were taken 1, 2, 3, and 7 days after herbicide application from different points on the leaves. Principal component analysis (PCA) was carried out on data normalized by the highest intensity band at 1522 cm^-1 and using spectral region from 950 to 1650 cm^-1 comprising mainly contributions of carotenoids. The carotenoids by intensive band at ∼1522 cm^-1 and bands with lower intensity at ∼1155 and 1007 cm^-1 in treated plants were confirmed. According to PC1 (the first principal component) and PC2 (the second principal component), the highest intensity bands responsible for treatment differentiation in C. album could be assigned to chlorophyll, lignin, and carotenes. According to PC1 in A. theophrasti leaves the treatment differences could be observed 7 days after mesotrione treatment and PC2 gave a clear separation between all control and treated leaf samples. Raman spectroscopy may be a good complement to invasive analytical methods, in assessing the plant abiotic stress induced by bleaching herbicides.