Contrasting canopy and fibrous root damage on Swingle citrumelo caused by ‘Candidatus Liberibacter asiaticus’ and Phytophthora nicotianae

Huanglongbing (HLB), associated with the phloem-limited bacterium, ‘Candidatus Liberibacter asiaticus’ (Las), is devastating trees in Florida citrus orchards. Phytophthora nicotianae (P.n.), omnipresent in citrus soils, causes root rot that reduces water and nutrient uptake by fibrous roots. To investigate fibrous root damage and replacement and canopy size in relation to infection of fibrous roots by P.n. and Las, rootstock seedlings of Swingle citrumelo (C. paradisi Macfad. × Poncirus trifoliata [L.] Raf.) were inoculated with Las or P.n. in two greenhouse pot trials. P.n. caused root damage within 5 weeks post inoculation, which led to greater reduction of canopy size than for Las-infected seedlings by the end of the experiment. Las increased fibrous root biomass accumulation at 5 weeks post root trimming (wpt) in the 2014 trial and at 11 wpt in the 2015 trial. New root length was not consistently increased by Las. Reduced total leaf area of asymptomatic Las-infected seedlings compared to non-inoculated controls might be due to the combined effect of altered carbohydrate allocation between shoots and roots and altered leaf morphology. This article is protected by copyright. All rights reserved.