Raman Spectroscopy for the Non-Invasive and Non-Destructive Analysis of Plants
Abstract
By the year 2050, the world’s population may exceed 9.8 billion, requiring 70% more food than we currently produce. Increased frequency of droughts and floods, spread of agricultural pests and pathogens, and application of harmful herbicides and pesticides threaten both our food supply and the health of the planet. While committing more space to agriculture may meet global food requirements, this solution would require massive agricultural development. Therefore, alternative means of increasing the food supply are essential.
Two promising methods for increasing agricultural output without committing more land are 1) protecting the crops we have, and 2) developing better crops. The first involves the development of advanced methods of crop surveillance to enable rapid response to stress, such as insufficient watering, insect infestation, or pathogen infection. The second, on the other hand, relies on selective breeding to generate stress-tolerant crops. Methods that can both detect stress in growing crops and identify plants with traits of interest as early as possible are essential for improving the global food supply.
Current methods for analyzing plants for stress and valuable traits include molecular methods, imaging methods, and spectroscopic methods. While these methods each have their own advantages, they are limited in many ways including expensive consumable reagents, inability to detect or differentiate between biotic and abiotic stress, and general inability to precisely assign what changes mean. Additionally, only one currently applied method, infrared spectroscopy, can determine molecular structures present in the sample. A non-invasive, non-destructive method that could enable rapid detection of chemical changes associated with stress or presence of valuable traits would be powerful for enhancing agricultural production.
Raman spectroscopy (RS) is a vibrational spectroscopic method with chemical structure specificity. It has been applied in many different fields, including (but not limited to) medicine, forensics, and polymer chemistry. Its ability to acquire chemical data non-invasively, non-destructively, and with a simple one-second-long scan makes it ideal for the rigors of modern commercial-scale agriculture. We describe the statistical methods that are commonly used for analyzing Raman spectra and demonstrate its use in the detection of stresses associated with insects, fungi, bacteria, viruses, and herbicides. We also show that RS can differentiate between plants of different species and between genotypes within species, and that this technology has the potential to analyze nutrient content non-invasively. With further development of the technology, Raman could drive a revolution in crop monitoring and breeding.
Citation
Farber, Charles B (2021). Raman Spectroscopy for the Non-Invasive and Non-Destructive Analysis of Plants. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /196275.