Multiplex real-time PCR for detection, identification and quantification of ‘Candidatus Liberibacter solanacearum’ in potato plants with zebra chip

Abstract

The new Liberibacter species, 'Candidatus Liberibacter solanacearum' (Lso) recently associated with potato/tomato psyllid-transmitted diseases in tomato and capsicum in New Zealand, was found to be consistently associated with a newly emerging potato zebra chip (ZC) disease in Texas and other southwestern states in the USA. A species-specific primer LsoF was developed for both quantitative real-time PCR (qPCR) and conventional PCR (cPCR) to detect and quantify Lso in infected samples. In multiplex qPCR, a plant cytochrome oxidase (COX)-based probe-primer set was used as a positive internal control for host plants, which could be used to reliably access the DNA extraction quality and to normalize qPCR data for accurate quantification of the bacterial populations in environment samples. Neither the qPCR nor the cPCR using the primer and/or probe sets with LsoF reacted with other Liberibacter species infecting citrus or other potato pathogens. The low detection limit of the multiplex qPCR was about 20 copies of the target 16S rDNA templates per reaction for field samples. Lso was readily detected and quantified in various tissues of ZC-affected potato plants collected from fields in Texas. A thorough but uneven colonization of Lso was revealed in various tissues of potato plants. The highest Lso populations were about 3x10(8) genomes/g tissue in the root, which were 3-order higher than those in the above-ground tissues of potato plants. The Lso bacterial populations were normally distributed across the ZC-affected potato plants collected from fields in Texas, with 60% of ZC-affected potato plants harboring an average Lso population from 10(5) to 10(6) genomes/g tissue, 4% of plants hosting above 10(7) Lso genomes/g tissue, and 8% of plants holding below 10(3) Lso genomes/g tissue. The rapid, sensitive, specific and reliable multiplex qPCR showed its potential to become a powerful tool for early detection and quantification of the new Liberibacter species associated with potato ZC, and will be very useful for the potato quarantine programs and seed potato certification programs to ensure the availability of clean seed potato stocks and also for epidemiological studies on the disease.

First report of ‘Candidatus Liberibacter solanacearum’ in the United Kingdom in the psyllid Trioza anthrisci

“…Ten specimens of T. anthrisci were tested using the real-time PCR assay of Li et al (2009). Five of six specimens from the UK and two of four samples from Sweden tested positive (Table 1).…”

PLS-DA Infrared Spectra Model of Citrus Leaves for the Characterization of Citrus Huanglongbing

“…Therefore, rapidly identification and removal of CLas-positive trees are useful for reduce the spread of HLB in citrus orchards and economic losses. However, traditional field assessment based on characteristics symptom is difficult since they resemble other diseases (such as stubborn disease and tristeza) and nutritional deficiencies [3][4][5]. At present, laboratory techniques, such as polymerase chain reaction (PCR) provide accurate detection of HLB [6], but PCR is an expensive and time-consuming process.…”

“…In another spectroscopy study, it was shown that the reflection of dried ground leaves in the mid-infrared band can be used to determine the HLB status of a sample with >95% accuracy [5]. Perez has demonstrated that Raman spectroscopy can be discriminated between orange plants HLB-positive and healthy plants with PCA-LDA analysis.…”

Candidatus Liberibacter solanacearum: detection, characterization, new hosts and epidemiology in Spain

“…and quantitative real-time PCR (Crosslin et al, 2011;Crosslin & Munyaneza 2009;Hansen et al, 2008;Li et al, 2009;Liefting et al, 2008Liefting et al, & 2009aLin et al, 2009;Lin et al, 2011a;Munyaneza et al, 2009b;Pitman et al, 2011;Ravindran et al, 2011a & b;Wen et al, & 2011. In addition, the detection of the bacterium in psyllids using PCR is relatively straightforward (Crosslin et al, 2011;Munyaneza et al, 2009b).…”

“…The uneven distribution and variation in the 'Ca. L. solanacearum' titer in different parts of infected potato plants has been observed, making the detection of this bacterium inconsistent using conventional PCR (Buchman et al, 2011b;Crosslin & Munyaneza, 2009;Li et al, 2009;Levy et al, 2011). 'Ca.…”