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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Plant Pathology Research » Research » Publications at this Location » Publication #320380
Title: Transmission and propagation of ‘Candidatus Liberibacter asiaticus’ by grafting with individual citrus leaves

Author
item Hilf, Mark
item Lewis, Reid

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2016
Publication Date: 5/1/2016
Publication URL: http://handle.nal.usda.gov/10113/62836
Citation: Hilf, M.E., Lewis, R.S. 2016. Transmission and propagation of ‘Candidatus Liberibacter asiaticus’ by grafting with individual citrus leaves. Phytopathology. 106:452-458.

Interpretive Summary: Liberibacter asiaticus (Las) is the bacteria which causes the citrus disease huanglongbing (HLB), which also is known as citrus greening. We developed a method for the transmission and propagation of Las whereby single asymptomatic or symptomatic leaves from Las-infected citrus trees are grafted to non-infected receptor citrus trees, with the subsequent transfer of Las bacteria to the receptor tree and the growth of the bacterial population and development of symptoms typical of HLB. This is an improvement in the standard methods for graft transmission and propagation of Las since we can infect much smaller citrus trees, saving space in the greenhouse and allowing a greater number of replicate trees per experiment. Grafting with single leaves creates a smaller scale model system for studying the interactions of Las and the citrus host.

Technical Abstract: Huanglongbing (HLB) is a chronic, progressive decline disease in citrus associated with systemic infection by the bacterium Candidatus Liberibacter asiaticus (CLas). Transmission in the field is by the Asian citrus psyllid (ACP), Diaphorina citri, Kuwayama. Experimental propagation of CLas is done commonly by grafting pieces of budwood from an infected plant. To produce a small scale model system for investigation of CLas biology, we investigated grafting single leaves from CLas-infected citrus plants as sources of inoculum for propagation of the bacterium. One hundred and sixty-two plants ranging in age from three to eighteen months were inoculated. Intact asymptomatic and HLB-symptomatic leaves infected 61/78 (78%) and 35/41 (85%) of grafted plants respectively. Inoculum consisting of the leaf petiole only or only an inoculum tissue remnant under the bark of the receptor tree gave 6/12 (50%) and 7/31 (23%) infected trees, respectively. Real-time PCR (qPCR) assays verified the infected status of plants, a majority of which developed the foliar blotchy-mottle symptom considered diagnostic for HLB, while some plants also displayed the stunted, chlorotic, non-growing shoots for which the disease is named. The qPCR data together with the symptoms displayed demonstrated individual leaves make effective inoculum sources for propagation of CLas.