engleski

Pathogenic complexes in plants and their silent players

Aim: Traditional views on plant diseases are mainly focused on a single etiological agent. Our case studies exemplify pathogenic complexes determining the host health status ; 1. oilseed rape with phyllody disease harbouring 'Candidatus Phytoplasma asteris' and Turnip mosaic virus (TuMV) and 2. Plectranthus scutellarioides (coleus) with fasciation hosting ‘Ca. P. solani’, Coleus blumei viroid 1 (CbVd-1), CbVd-3 and Coleus vein necrosis virus (CVNV). Methods: Phytoplasmas were characterized from total nucleic acids by amplification and analyses of 16S rRNA gene and multigene sequence analyses of 4-5 other genes. Viroids and viruses were identified from extracted RNAs by RT-PCR and phylogenetic analyses. Virus presence was also tested biologically. In coleus, high throughput sequencing (HTS) was performed on Illumina Nextseq 500 platform. Results: In the rape displaying phyllody disease symptoms, ‘Ca. P. asteris’ was confirmed and the phytoplasma had significant SNPs in the amp gene encoding a specific protein essential for aphid transmission. TuMV co-infecting rapes, from the World-B phylogenetic lineage, added to the disease severity. In coleus with fasciation, a pathogenic complex consisted of two viroids (CbVd-1 and -3), a phytoplasma (‘Ca. P. solani’), and a carlavirus (CVNV). The virus presence was first deduced from HTS data and later confirmed by RT-PCR and biotests. Even though CVNV was expected to cause some symptoms in coleus, it remained silent in this pathogenic complex. Conclusions: Plants may harbour diverse pathogenic complexes causing diseases or asymptomatic infections. HTS facilitates the discovery of these complexes prompting us to revisit the paradigms of plant-pathogen interactions.

coleus fasciation, oilseed rape phyllody, phytoplasmas, viruses, viroids

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