Studies on the tuber transmission of ‘Candidatus Liberibacter solanacearum’
Studies have been conducted in New Zealand to evaluate the possible role of potato tubers in the transmission of ‘Candidatus Liberibacter solanacearum’ (EPPO A1 List – bacterium associated with zebra chip disease). Potato tubers infected with ‘Ca. L. solanacearum’ were planted in the absence of the psyllid vector (Bactericera cockerelli - EPPO A1 List) and the progeny obtained was tested by nested-PCR. In this experiment, 62 infected and 38 healthy potato tubers were planted (under a net to prevent psyllid infestation) and the development of symptoms was monitored between planting of the mother tubers and the resulting crop. In the resulting crop, the transmission ‘Ca. L. solanacearum’ was evaluated with the development of foliar and tuber symptoms, and positive results in nested-PCR tests. A large proportion of mother tubers (58) sprouted. During the growing season, only 2 plants (out of the 58 obtained) showed symptoms of zebra chip; they died prematurely and the presence of the pathogen could be detected in leaf samples. The remaining 56 potato plants did not show any foliage symptoms. However, when tested the pathogen could be found in foliar samples from 39 of these potato plants. At the end of the growing season, harvested progeny tubers were screened for the presence of zebra chip symptoms and tested. Mild symptoms were observed in tubers which had been produced by 1 plant only. Nested-PCR tests of tuber samples (1 representative tuber collected from each harvested plant) confirmed that ‘Ca. L. solanacearum’ was present in the daughter tubers showing mild symptoms, as well as in tubers originating from 4 asymptomatic plants. These results showed that ‘Ca. L. solanacearum’ can be transmitted from the mother tubers both to the foliage of growing plants and to progeny tubers.
Sources
Pitman AR, Drayton GM, Kraberger SJ, Genet RA, Scott IAW (2011) Tuber transmission of 'Candidatus Liberibacter solanacearum' and its association with zebra chip on potato in New Zealand. European Journal of Plant Pathology 129(3), 389-398.