Journal of Citrus Pathology

Huanglongbing (HLB) is associated with the phloem-limited bacterium, Candidatus Liberibacter asiaticus (Las). Phytophthora nicotianae (P.n.) causes root rot of citrus, which reduces water and nutrient uptake by citrus fibrous roots. The discovery that Las damage to fibrous roots occurs before tree canopy symptoms develop led to the prediction that Las root infection directly damages roots and may interact with soil-borne pathogens to cause further damage. Hence, comparison of root damage by Las and P.n. alone or in combination was carried out on seedlings of Cleopatra mandarin (Citrus reticulata Blanco) rootstock to evaluate the possible interaction of Las and P.n. and their relative contribution to fibrous root loss. The results demonstrated that i) roots of seedlings have a similar level of damage when inoculated with Las or P.n., and coinoculation causes comparable damage as each pathogen alone; and ii) Las infection increases and decreases P.n. infection incidence overtime without following a clear progression.