Huanglongbing (HLB) is presumptively caused by a phloem limited bacteria. In citrus there are three forms of concern, the Asian, African and American forms. The Asian form of HLB expresses symptoms in both cool and warm conditions. The African form of HLB expresses symptoms only in cool conditions (20-250 C, 68-770 F). Both isolates can be vectored by the Asian citrus psyllid Diaphorina citri (Kuwayana) and by the psyllid Trioza erytreae (Del Guercio). The American form was identified in Brazil in 2004 and is transmitted by D. citri there.
HLB can be graft transmitted but transmission rates are variable because of irregular distribution of bacteria within the host plant. Seed transmission may be possible but studies are not yet conclusive and if it occurs it is only at very low levels and the disease does not seem to persist beyond early seedling stages. The most important method of disease spread occurs by the two species of psyllids that serve as vectors. HLB can be acquired by both nymphs and adults, which can maintain and transmit the disease throughout their 3- to 4-month lifespan. HLB is systemic and has an incubation period of three months to multiple years before symptoms are visible.
Other Common Names
Greening, yellow shoot, yellow dragon
Serrano, D., Serrano, E., Dewdney, M., and Southwick, C. (2010). Citrus Diseases. USDA/APHIS/PPQ Center for Plant Health Science and Technology. [09-14]