Submitted to: Journal of Applied Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 2, 2009
Publication Date: May 1, 2009
Citation: Calderon, F.J., Acosta Martinez, V., Douds, D.D., Reeves III, J.B., Vigil, M.F. 2009. Mid-Infrared and Near Infrared Spectral Properties of Mycorrhizal and Non-Mycorrhizal Root Cultures. Journal of Applied Spectroscopy. 63(5)494-500. Interpretive Summary: Mycorrhizal fungi can be very beneficial to crops because they grow into plant roots and aid in the absorption of nutrients and water from soil, which often results in increased crop yields. This study describes a possible new technology to detect mycorrhizal fungi in roots using infrared light, which can possibly simplify and speed up the measurement of mycorrhizae in field collected root samples.
Technical Abstract: We investigated the Fourier-transformed mid-infrared (MidIR) and near infrared (NIR) spectroscopic properties of mycorrhizal (M) and non-mycorrhizal (NM) Ri T-DNA transformed carrot roots with the goal of finding infrared markers for colonization by arbuscular mycorrhizal (AM) fungi. The roots were cultured with or without the AM fungus Glomus intraradices under laboratory conditions. A total of 50 M and NM samples were produced after pooling subsamples. The roots were dried, ground, and scanned separately for the NIR and MidIR. The root samples were analyzed for fatty acid composition in order to confirm mycorrhizal infection and determine the presence of fatty acid markers. Besides the roots, fatty acid standards, pure cultures of saprophytic fungi, and chitin were also scanned in order to identify spectral bands likely to be found in M samples. Principal Components Analysis (PCA) was used to illustrate spectral differences between the M and NM root samples. The NIR achieved better resolution than the MidIR, because no pre-treatment was needed to get good resolution in the PCA analysis of the NIR data. Standard normal variate and detrending pretreatment improved the resolution between M and NM in the MidIR range. The PCA loadings and/or the spectral subtraction of selected samples shows that M roots are characterized by absorbances at or close to 400 cm-1, 1100-1170 cm-1, 1690 cm-1, 2928 cm-1, and 5032 cm-1. The NM samples had characteristic absorbances at or near 1734 cm-1, 3500 cm-1, 4000 cm-1, 4389 cm-1, and 4730 cm-1. Some of the bands that differentiate M from NM roots are prominent in the spectra of pure fungal cultures, chitin, and fatty acids. Our results show that mycorrhizal and nonmycorrhizal root tissues can be differentiated via MidIR and NIR spectra with the advantage that the same samples can then be used for other analyses.