Cultivation of ‘Candidatus Liberibacter asiaticus’, ‘Ca. L. africanus’ and ‘Ca. L. americanus’
Huanglongbing (EPPO A1 List) is a citrus disease associated with several phloem-limited bacteria which had previously not been able to be cultured (in particular to verify Kochs’ postulates). A new growing medium (called Liber A) has been designed and used successfully to cultivate the three species of ‘Candidatus Liberibacter’ associated with huanglongbing (i.e. ‘Ca. Liberibacter asiaticus’, ‘Ca. L. africanus’ and ‘Ca. L. americanus’). Two strains of ‘Ca. L. asiaticus’ and one strain of ‘Ca. L. americanus were found to be pathogenic on citrus and were re-isolated from tissues of inoculated trees and seedlings 9 and 2 months after inoculation (by leaf infiltration), respectively. It is considered that Koch’s postulates have not been fully completed by inoculating mature trees and reproducing the entire disease etiology. However, this partial fulfilment of Kochs’ postulates showed that both ‘Ca. L. asiaticus’ and ‘Ca. L. americanus’ are pathogens of citrus, causing huanglongbing–like symptoms, and are likely to be major components of the disease (although it cannot be excluded that the disease might be a syndrome involving other factors).
Sources
Secher A, Schuenzel EL, Cooke P, Donnua S, Thaveechai N, Postnikova E, Stone AL, Schneider WL, Damsteegt VD, Schaad NW (2009) Cultivation of ‘Candidatus Liberibacter asiaticus’, ‘Ca. L. africanus’ and ‘Ca. L. americanus’ associated with huanglongbing. Phytopathology 99(5), 480-486.