Submitted to: American Phytopathology Society
Publication Type: Abstract Only
Publication Acceptance Date: March 13, 2008
Publication Date: N/A
Technical Abstract: Canadidatus Liberibacter asiaticus (Las) is the most widely-distributed of three species of Liberibacter that are associated with citrus Huanglongbing (HLB), a lethal disease of citrus worldwide. In addition to citrus, periwinkle (Catharanthus roseus) and dodder (Cuscuta pentagona) are two experimental hosts in which the bacteria can multiply well. Symptoms of HLB in inoculated-periwinkle were characterized by progressive vein and leaf yellowing, resulting in death of most HLB-infected periwinkles within six month after first appearance of symptoms. Dodder plants did not exhibit symptoms, even when they contain high titers of the bacterium. Las was detected in up to 53% of all seeds tested both from HLB-infected periwinkle and dodder without resorting to nested PCR. The PCR amplicons were confirmed by sequence analysis. Germination rates of these Las-positive seeds from both plant species were normal. Over 80% of the periwinkle plants germinated from the infected seeds showed initial HLB symptoms of vein yellowing and leaf yellowing only when they were stressed by nutrient deficiency. Surprisingly, the disease progressed slowly, and did not cause plant death, and all symptomatic plants became asymptomatic after the stress was removed. The Las population remained in very low titer; in most cases, detected only by nested PCR or regular PCR by increasing the concentration of the bacterial DNA. The periwinkles-infected with Las via seed transmission have been maintained for over six months. These results suggest that although Las was seed transmitted, a second, undescribed component of an HLB disease complex was not.