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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 #368146
Research Project: Mitigating High Consequence Domestic, Exotic, and Emerging Diseases of Fruits, Vegetables, and Ornamentals

Location: Subtropical Plant Pathology Research

Title: Inoculation period and citrus host effect establishment of new infections of ‘Candidatus Liberibacter asiaticus’ transmitted via vegetative grafting

Author
item Hilf, Mark
item LUO, WEIQU - North Carolina State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2020
Publication Date: 5/20/2020
Citation: Hilf, M.E., Luo, W. 2020. Inoculation period and citrus host effect establishment of new infections of ‘Candidatus Liberibacter asiaticus’ transmitted via vegetative grafting. Plant Disease. 104:1894-1899. https://doi.org/10.1094/PDIS-09-19-2022-RE.
DOI: https://doi.org/10.1094/PDIS-09-19-2022-RE

Interpretive Summary: Vegetative grafting is a common method of transmitting Candidatus Liberibacter asiaitucs (CLas), the bacteria that causes the citrus disease HLB. To transmit and propagate the bacteria researchers graft infected citrus tissue to a non-infected tree and leave the tissue in place for a time known as the inoculation period (IP), which can exceed 6 months, to insure infection. We wanted to know if the length of the IP and the type of citrus trees affected transmission. We found that IPs as short as 21 days can lead to an infection, but periods of 51 or 81 days led to more infection, although results for 51 and 81 days were similar. Sweet orange was significantly more susceptible to infection than five other types of citrus, regardless of the IP. Sweet orange is considered highly susceptible to development of HLB, and this may be because CLas can colonize sweet orange trees with fewer bacteria in a shorter time than for other citrus types.

Technical Abstract: Vegetative grafting is a common method of transmitting and propagating ‘Candidatus L. asiaticus’, the bacterial species accepted as the causal agent of the citrus disease huanglongbing (HLB). Generally, infected tissue is grafted to a receptor tree and left in place indefinitely to insure transmission. In this study, individual HLB-symptomatic leaves were grafted as inoculum sources to receptor trees of six citrus types and removed after inoculation periods (IP) of 21, 51 or 81 days to assess the effect of varying inoculum periods on transmission of bacteria to and their establishing a new infection in receptor trees. Analysis of data from three trials showed a significantly reduced proportion of infected trees with an IP of 21 days compared to 51 and 81 days, but that there was no significant difference between IPs of 51 and 81 days. At the end of a testing period exceeding 300 days after inoculum removal, only 20% of trees were infected after an IP of 21 days, compared to nearly 75% with an IP of 81 days within a testing period not exceeding 250 days. Infection of sweet orange trees was significantly higher than for trees of C. macrophylla, mandarin, sour orange, grapefruit and rough lemon throughout the experiment. There was no significant difference between the infection probabilities of these latter five citrus types. The data from this study indicates that successful infection by grafting is dependent upon the time of exposure to the inoculum and that sweet orange is significantly more susceptible to colonization by ‘Ca. L. asiaticus’ when the exposure to inoculum is limited.