Lateral flow immunoassay for on-site detection of <i>Xanthomonas arboricola</i> pv. <i>pruni</i> in symptomatic field samples

<div><p><i>Xanthomonas arboricola</i> pv. <i>pruni</i> is a quarantine pathogen and the causal agent of the bacterial spot disease of stone fruits and almond, a major threat to <i>Prunus</i> species. Rapid and specific detection methods are essential to improve disease management, and therefore a prototype of a lateral flow immunoassay (LFIA) was designed for the detection of <i>X</i>. <i>arboricola</i> pv. <i>pruni</i> in symptomatic field samples. It was developed by producing polyclonal antibodies which were then combined with carbon nanoparticles and assembled on nitrocellulose strips. The specificity of the LFIA was tested against 87 <i>X</i>. <i>arboricola</i> pv. <i>pruni</i> strains from different countries worldwide, 47 strains of other <i>Xanthomonas</i> species and 14 strains representing other bacterial genera. All <i>X</i>. <i>arboricola</i> pv. <i>pruni</i> strains were detected and cross-reactions were observed only with four strains of <i>X</i>. <i>arboricola</i> pv. <i>corylina</i>, a hazelnut pathogen that does not share habitat with <i>X</i>. <i>arboricola</i> pv. <i>pruni</i>. The sensitivity of the LFIA was assessed with suspensions from pure cultures of three <i>X</i>. <i>arboricola</i> pv. <i>pruni</i> strains and with spiked leaf extracts prepared from four hosts inoculated with this pathogen (almond, apricot, Japanese plum and peach). The limit of detection observed with both pure cultures and spiked samples was 10⁴ CFU ml^-1. To demonstrate the accuracy of the test, 205 samples naturally infected with <i>X</i>. <i>arboricola</i> pv. <i>pruni</i> and 113 samples collected from healthy plants of several different <i>Prunus</i> species were analyzed with the LFIA. Results were compared with those obtained by plate isolation and real time PCR and a high correlation was found among techniques. Therefore, we propose this LFIA as a screening tool that allows a rapid and reliable diagnosis of <i>X</i>. <i>arboricola</i> pv. <i>pruni</i> in symptomatic plants.</p>