Contents lists available at ScienceDirect Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag In-field measurement of starch content of cassava tubers using handheld vis- near infrared spectroscopy implemented for breeding programmes Kanvisit Maraphum a , Khwantri Saengprachatanarug a,b,c , Seree Wongpichet a , Arthit Phuphaphud a , Jetsada Posom a,b,c, ⁎ a Department of Agricultural Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand b Applied Engineering for Important Crops of the North East Research Group, Khon Kaen University, Khon Kaen 40002, Thailand c Bio-Sensing and Field Robotic Laboratory, Khon Kaen University, Khon Kaen 40002, Thailand ARTICLE INFO Keywords: Cassava tubers Starch content Breeding programme Near-infrared Spectroscopic technique ABSTRACT This paper involves the prediction of cassava tuber starch content (SC) using near-infrared (NIR) spectroscopy, aiming to follow the change of SC in individual tubers utilised for a breeding programme. This study applies a portable NIR spectrometer at wavelengths of 570–1031 nm in the evaluation of SC in fresh cassava tubers. The prediction models are established using partial least squares (PLS) regression with NIR spectra obtained in the interactance mode. The effective model was developed from the wavelength region of 600–1000 nm with spectral pre-processing of the second derivative, giving the coefficient of determination of prediction set (r 2 ) and root mean square error of prediction (RMSEP) of 0.62 and 2.21%, respectively. The effect of tuber section (including head, middle and tail) on the performance of the SC model was investigated. The individual head, middle and tail models were acceptable for screening. However, the performances of the combined model (which is the model developed a mix of all individual section samples) and the individual section model were not significantly different. Therefore, the combined model was suitable in real application because of the ease of in- field scanning. The result demonstrates that the SCs of cassava tubers can be measured by a NIR spectroscopy method. Furthermore, it can be used as an alternative tool which is appropriate for breeders to use to follow the behaviour of SC during breeding. 1. Introduction Cassava (Manihot esculenta) is an important economic crop. It has been utilised as a raw material for producing food and bioenergy. Thailand is the second-largest producer of cassava in the world and has the highest export value coming from cassava products (OAE, 2018). All parts of cassava are valuable. Cassava root is used to produce food, animal feed and biofuel (ethanol). Other parts, such as leaves, stalks and rhizomes, are used as raw materials in various industries, such as power plants, pelletisation factories and so on (KURDI., 2015a; Koopmans, 2005). In the commercial market, the price of cassava root is set by its weight, moisture content (MC) and starch content (SC). The SC is an especially key index of the quality and value of cassava root (Buddhakulsomsiri et al., 2015; Mulualem and Bekeko, 2015). Cassava with higher SC is sold at a high price. Therefore, the variety that can provide the highest SC, store SC the fastest and keep SC constant as long as possible is required for breeding and farming (Buddhakulsomsiri et al., 2015; Chuasuwan, 2018). The SC and yield of cassava root can vary according to the planting conditions, such as soil moisture content, temperature, soil fertiliser and environmental surroundings. Therefore, if a good variety is planted but in a different season and different area, then it may not provide high quality and productivity (Janket et al., 2018). Even with the same variety, if the planting conditions are changed, SC and productivity can be different. To maintain and in- crease quality and productivity, it is necessary to develop a specific variety always suited to the culture. Moreover, because of climate change, a new variety has to be improved more often because the current variety will not have good quality in the future. Presently, the lead time of cassava breeding is long and has a rather low accuracy, waiting for more than 15 years before release to farmers (KURDI, 2015b). For the breeding protocol, after pollination to produce hybrids and waiting to get cloned hybrid seeds, each seed is an in- dividual variety. Each seed (each variety) is planted to select the best variety among hybrid populations. When the cassava age reaches 12 months, the breeder must compare the yield of tubers and other important agronomic traits of the cloned hybrids. In this step, each https://doi.org/10.1016/j.compag.2020.105607 Received 6 March 2020; Received in revised form 20 May 2020; Accepted 24 June 2020 ⁎ Corresponding author at: Department of Agricultural Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand. E-mail address: jetspo@kku.ac.th (J. Posom). Computers and Electronics in Agriculture 175 (2020) 105607 0168-1699/ © 2020 Elsevier B.V. All rights reserved. T