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

Derival Derival,Zhang Zhang,Albrecht Albrecht,Ampatzidis Ampatzidis

doi:10.3390/agronomy9070354

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.

Highlights

The demand for new and superior rootstocks has tremendously increased since the arrival of the devastating citrus disease huanglongbing (HLB or citrus greening) in Florida in 2005
When the soil moisture on ground-penetrating radar (GPR) and detection was evaluated, the results indicated that thearchitecture
Single-factor and multi-factor field experiments were conducted to evaluate the suitability of a GPR to analyze the citrus tree root systems in an agricultural field setting

Summary

Introduction

The demand for new and superior rootstocks has tremendously increased since the arrival of the devastating citrus disease huanglongbing (HLB or citrus greening) in Florida in 2005. HLB is a bacterial disease of the phloem and an insect vector spreads it (Asian citrus psyllid). HLB leads to tree decline several years after infection and it has decimated citrus industries worldwide [1,2,3]. In Florida, the economic impact of HLB has been estimated to have caused a loss of more than $4 billion in cumulative industry output, or an annual average of $1 million during the production seasons from 2012 to 2016 [4]. Field trials have demonstrated that the use of specific rootstocks can increase the productivity of commercially grown citrus trees in an HLB-endemic environment [6]. Root architectural differences play a major role in tolerance to wind-induced uprooting, an effect that is important in Florida, which is vulnerable to frequent tropical storms and hurricanes

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