Water stress is a serious concern in the citrus industry due to its effect on citrus quality and yield. A sensor system for early detection will allow rapid implementation of control measures and management decisions to reduce any adverse effects. Laser-induced breakdown spectroscopy (LIBS) presents a potentially suitable technique for early stress detection through elemental profile analysis of the citrus leaves. It is anticipated that the physiological change in plants due to stress will induce changes in the element profile. The major goal of this study was to evaluate the performance of laser-induced breakdown spectroscopy as a method of water stress detection for potential use in the citrus industry. In this work, two levels of water stress were applied to Cleopatra (Cleo) mandarin, Carrizo citrange, and Shekwasha seedlings under the controlled conditions of a greenhouse. Leaves collected from the healthy and stressed plants were analyzed using LIBS, as well as with a spectroradiometer (visible-near infrared spectroscopy) and a thermal camera (thermal infrared). Statistical classification of healthy and stressed samples revealed that the LIBS data could be classified with an overall accuracy of 80% using a Na?ve-Bayes and bagged decision tree-based classifiers. These accuracies were lower than the classification accuracies acquired from visible-near infrared spectra. An accuracy of 93% and higher was achieved using a bagged decision tree with visible-near infrared spectral reflectance data.
References
[1]
Ballester, C.; Castel, J.; Intrigliolo, D.D.; Castel, J.R. Response of clementina de nules citrus trees to summer deficit irrigation yield components and fruit composition. Agric. Water Manag. 2011, 98, 1027–1032, doi:10.1016/j.agwat.2011.01.011.
[2]
Radziemski, L.; Cremers, D. A brief history of laser-induced breakdown spectroscopy: From the concept of atoms to LIBS 2012. Spectrochim. Acta Part B 2013, 87, 3–10, doi:10.1016/j.sab.2013.05.013.
[3]
Trevizan, L.C.; Santos, D., Jr.; Samad, R.E.; Vieira, N.D., Jr.; Nomura, C.S.; Nunes, L.C.; Rufini, I.A.; Krug, F.J. Evaluation of laser induced spectroscopy for the determination of macronutrients in plant materials. Spectrochim. Acta Part B 2008, 63, 1151–1158, doi:10.1016/j.sab.2008.08.005.
[4]
Trevizan, L.C.; Santos, D., Jr.; Samad, R.E.; Nunes, L.C.; Rufini, I.A.; Krug, F.J. Evaluation of laser induced spectroscopy for the determination of micronutrients in plant materials. Spectrochim. Acta Part B 2009, 64, 369–377, doi:10.1016/j.sab.2009.04.003.
[5]
Kim, G.; Kwak, J.; Choi, J.; Park, K. Detection of nutrient elements and contamination by pesticides in spinach and rice samples using Laser-Induced Breakdown Spectroscopy (LIBS). J. Agric. Food Chem. 2012, 60, 718–724, doi:10.1021/jf203518f.
[6]
Yao, M.; Huang, L.; Zheng, J.; Fan, S.; Liu, M. Assessment of feasibility in determining of Cr in gannan navel orange treated in controlled conditions by Laser Induced Breakdown Spectroscopy. Opt. Laser Technol. 2013, 52, 70–74, doi:10.1016/j.optlastec.2013.04.005.
[7]
Chapin, F.S., III. Integrated response of plants to stress. Bioscience 1991, 41, 29–36, doi:10.2307/1311538.
[8]
Carter, G.A. Primary and secondary effects of water content on the spectral reflectance of leaves. Am. J. Bot. 1991, 78, 916–924, doi:10.2307/2445170.
[9]
Kriston-Vizi, J.; Umeda, M.; Miyamoto, K. Assessment of water status of mandarin and peach canopies using visible multispectral imagery. Precis. Agric. 2008, 100, 338–345.
Ballester, C.; Castel, J.; Jimenez-Bello, M.A.; Castel, J.R.; Intrigliolo, D.S. Thermographic measurement of canopy temperature is a useful tool for predicting water deficit effects on fruit weight in citrus trees. Agric. Water Manag. 2013, 122, 1–6, doi:10.1016/j.agwat.2013.02.005.
[12]
Garcia-Sanchez, F.; Syvertsen, J.P.; Gimeno, V.; Botia, P.; Perez-Perez, J.G. Responses to flooding and drought stress by two citrus rootstock seedlings with different water-use efficiency. Physiol. Plant. 2007, 130, 532–542, doi:10.1111/j.1399-3054.2007.00925.x.