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bioRxiv · 10.1101/821553

Potential soil transmission of a novel Candidatus Liberibacter strain detected in citrus seedlings grown in soil from a huanglongbing infested citrus grove

Nunes da Rocha, U.·Shin, K.·Timilsina, S.·Jones, J. B.·Singer, B. H.·van Bruggen, A. H. C.
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Abstract

Candidatus Liberibacter spp. are Alphaproteobacteria associated with plants and psyllid vectors. Most cause plant diseases, including Ca Liberibacter asiaticus (Las) associated with citrus huanglongbing (HLB). Replacing HLB-infected by Las-free citrus trees results in fast re-infection despite psyllid control. To check if HLB could be soil-borne, we performed an insect-free greenhouse-experiment with 130 mandarin seedlings in two citrus-grove soils (A and B), non-autoclaved or autoclaved. Liberibacter-specific 16S-rDNA PCR primers to detect Las were used to search for Ca. Liberibacter spp. in mandarin leaves. Seven plants grown in non-autoclaved soil B showed HLB-like symptoms and tested positive after 2.5 and 8.5 months using three different primer systems: two based on the 16S-rDNA gene (primers HLBas/HLBr and OI2c/OI1) and one based on the rplA/rplJ gene (primers LAA2/LAJ5). DNA segments from these plants amplified by primers OI2c/OI1 were cloned and sequenced; they were 95.9 % similar to Las and 94.8% to Ca. Liberibacter africanus (Laf). The DNA product from Liberibacter-group specific PCR primers for the rplA/rplJ gene was 87.6% similar to that of Las and 78.2% of Laf. As the strain obtained originated from soil and was different from existing Ca. Liberibacter species, this strain may be a new species.

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Nunes da Rocha, U., Shin, K., Timilsina, S., Jones, J. B., Singer, B. H., van Bruggen, A. H. C.. 2019-10-29. Potential soil transmission of a novel Candidatus Liberibacter strain detected in citrus seedlings grown in soil from a huanglongbing infested citrus grove. https://doi.org/10.1101/821553

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