Challenges facing the detection of systemic pathogens in certification programs
Viruses, phytoplasmas and a few species from bacteria and fungi transmit systemically within plant tissues. As no effective control measures have been developed for systemic pathogens, the most effective way to prevent their introduction into orchards is the use of certified and pathogen-free planting materials. However, certification of planting materials demands sensitive and reliable methods for pathogen detection. Several detection methods on the basis of proteins (e.g., enzyme-linked immunosorbent assay (ELISA), dot blot immunoassay (DIBA), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), nucleic acids e.g., polymerase chain reaction (PCR) and its derivatives like reverse transcription-PCR, (RT-PCR)) and indexing of pathogens on indicator plants (biological indexing) have been developed for pathogen detection in pure and applied sciences. Each of those methods has its own advantages, but their application in biological indexing (with the exception of nuclear stocks) are limited in certification programs due to labor, costs and time. ELISA and DIBA are not sensitive enough and require specific antibodies for each virus. Specific antibodies are not commercially available for some viruses and for pathogens like viroids, ELISA and DIBA are not applicable. Assays like SDS-PAGE are not applicable for reliable detection of pathogens, specifically viruses and viroids, in young plants and saplings due to low concentration of these pathogens. In spite of higher sensitivity and reliability of PCR-based detection methods, there are several challenges including purity of RNA and DNA templates, false positive and false-negative results, presence of inhibitors and, most importantly, the necessity for designing isolate-specific primers. The present article will focus on details of the advantages and disadvantages of all three methods in detection of viruses and phytoplasmas resulting from ten years of experience in working on certification of different groups of planting materials.
Naderpour, M. (2020). Challenges facing the detection of systemic pathogens in certification programs. Acta Hortic. 1269, 89-96
pathogen detection, nucleic acid, protein, biological indexing, planting materials