Evaluation of a Ground Penetrating Radar to Map the Root Architecture of HLB-Infected Citrus Trees

Abstract

This paper investigates the influences of several limiting factors on the performance of ground penetrating radar (GPR) in accurately detecting huanglongbing (HLB)-infected citrus roots and determining their main structural characteristics. First, single-factor experiments were conducted to evaluate GPR performance. The factors that were evaluated were (i) root diameter; (ii) root moisture level; (iii) root depth; (iv) root spacing; (v) survey angle; and, (vi) soil moisture level. Second, two multi-factor field experiments were conducted to evaluate the performance of the GPR in complex orchard environments. The GPR generated a hyperbola in the radar profile upon root detection; the diameter of the root was successfully determined according to the width of the hyperbola when the roots were larger than 6 mm in diameter. The GPR also distinguished live from dead roots, a capability that is indispensable for studying the effects of soil-borne and other diseases on the citrus tree root system. The GPR can distinguish the roots only if their horizontal distance is greater than 10 cm and their vertical distance is greater than 5 cm if two or more roots are in proximity. GPR technology can be applied to determine the efficacy of advanced crop production strategies, especially under the pressures of disease and environmental stresses.

Recent advances in methods for in situ root phenotyping

“… (A) Xray computed tomography (CT) ( Hou et al, 2022 ); (B) magnetic resonance imaging (MRI) ( Daniel et al, 2022 ); (C) ground penetrating radar (GPR) ( Zhang et al, 2019 ); (D) electrical capacitance (EC) ( Schierholt et al, 2019 ); (E) electrical impedance tomography (EIT) ( Corona et al, 2019 ) (F) neutron tomography (NT) ( Krzyzaniak et al, 2021 ). 1.…”

“…Ultimately, these reflections can be quantified and generated into a 3D field, allowing for root visualization ( Alnuaimy et al, 2000 ; Jol, 2009 ; Liu et al, 2018 ). GPR has been widely used to measure the coarse root (diameter >2 mm) of trees and shrub species, such as cassava ( Delgado et al, 2017 ), loblolly pine ( Butnor et al, 2001 ), elm ( Li et al, 2013 ), willow ( Li et al, 2015 ), and citrus ( Zhang et al, 2019 ). Liu et al (2018) scanned winter and cane roots using GPR (1,600 MHz) and found significant relations between GPR indices and root parameters, implying that GPR can be applied to phenotype crop roots.…”

Sensing Methodologies in Agriculture for Monitoring Biotic Stress in Plants Due to Pathogens and Pests

“…Two terrestrial LiDAR systems (operating at 905 nm and 1550 nm) were used to measure 29 mature Norway spruce trees that showed mild to moderate symptoms. Several intensity metrics were derived from LiDAR data as inputs and LDA-based analysis was performed yielding an average classification accuracy of about 66%; (ii) evaluation of a GPR-based system for detection HLB infection in citrus trees by mapping their root architecture [177]. A GPR (TRU™ Model, Tree Radar, Inc., Silver Spring, MA, USA) equipped with a 1600 MHz antenna was mounted on a mobile cart to generate root morphology.…”

Evaluation of the effects of elevated CO2 concentrations on the growth of cassava storage roots by destructive harvests and ground penetrating radar scanning approaches

“…However, this method collects information from just one section of the roots and is thus not well suited for large storage roots and tubers for which only a small portion of the structure can be imaged. There is no established field technique for monitoring storage root development across a full growing season (e.g., Zhang et al, 2019 ).…”