Paper · 2026 · Journal of Microbiological Methods

A qPCR method for detection of ‘Candidatus Liberibacter asiaticus’: Optimization of selected assay parameters

Jonathan Phillips; Sohrab Bodaghi; José Á. Sánchez Gómez; et al.

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Open access · cc-by

Abstract

'Candidatus Liberibacter asiaticus' (CLas), the presumed causative agent of Huanglongbing (HLB, citrus greening), threatens citrus production worldwide. With no cure available, infected trees decline rapidly and entire groves can be lost. Slowing the spread of HLB depends on early, accurate detection of CLas and prompt removal of infected trees. In California, quantitative polymerase chain reaction (qPCR) remains the gold standard test. Reaching the theoretical detection limit-detecting a single CLas cell in a sample-requires tuning the full workflow, not just the primers and probe. Here, we tested four practical levers: PCR plate color (clear, black, and white); pipetting consistency; reported PCR enhancers; and the addition of a reverse transcription step to enable RT-qPCR on total nucleic acid extracts. White plates increased fluorescence signal and tightened Ct values across replicates. Improved pipetting reduced operator-dependent variability. Among the tested enhancers, 1-2% glycerol improved detection at low CLas titer levels. Adding reverse transcription lowered Ct values by at least 5 cycles, improving detection by at least ∼32-fold. Together, these low-cost changes push routine qPCR toward single-bacterium detection while reducing variability in CLas surveillance.

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Claims 6

Method / resourceobservedoriginal resultmeasured

Claim · model-written summary

White plates increased fluorescence signal.

Outcome
fluorescence signale0
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increasede0
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platese0

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e0

“White plates increased fluorescence signal and tightened Ct values across replicates”

✓ located verbatim in the source · abstract, characters 818–902 · show in text ↑
Method / resourceobservedoriginal resultmeasured

Claim · model-written summary

White plates tightened replicate Ct values.

Outcome
Ct valuese0
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tightenede0
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platese0

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e0

“White plates increased fluorescence signal and tightened Ct values across replicates”

✓ located verbatim in the source · abstract, characters 818–902 · show in text ↑
Method / resourceobservedoriginal resultmeasured

Claim · model-written summary

Improved pipetting reduced operator-dependent variability.

Outcome
operator-dependent variabilitye0
Direction
reducede0
Comparator
pipettinge0

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e0

“Improved pipetting reduced operator-dependent variability”

✓ located verbatim in the source · abstract, characters 904–961 · show in text ↑
Method / resourceobservedoriginal resultmeasured

Claim · model-written summary

One to two percent glycerol improved detection at low pathogen titer.

Outcome
detection at low CLas titer levelse0
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improvede0
Value
1-2%e0

Not reportedTaxon

Verbatim

e0

“1-2% glycerol improved detection at low CLas titer levels”

✓ located verbatim in the source · abstract, characters 991–1048 · show in text ↑
Method / resourceobservedoriginal resultmeasured

Claim · model-written summary

Reverse transcription lowered Ct by at least five cycles.

Outcome
Ct valuese0
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lowerede0
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at least 5 cyclese0

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e0

“Adding reverse transcription lowered Ct values by at least 5 cycles”

✓ located verbatim in the source · abstract, characters 1050–1117 · show in text ↑
Method / resourceobservedoriginal resultmeasured

Claim · model-written summary

Reverse transcription improved detection by at least approximately 32-fold.

Outcome
detectione0
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improvinge0
Value
at least ∼32-folde0

Not reportedTaxon

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e0

“improving detection by at least ∼32-fold”

✓ located verbatim in the source · abstract, characters 1119–1159 · show in text ↑