Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 2011
Publication Date: February 10, 2012
Citation: Crosslin, J., Hamm, P., Rondon, S., Eggers, J., Munyaneza, J.E. 2012. First report of zebra chip disease and Candidatus Liberibacter solanacearum on potatoes in Oregon and Washington State. Plant Disease. 96:452.
Interpretive Summary: The zebra chip (ZC) disease is a serious and emerging disease of potatoes. The disease has been reported in various parts of the south-western US, Mexico, Central America, and recently in New Zealand. In September of 2011, symptoms consistent with the ZC disease were observed in potato tubers grown in northern Oregon and southern Washington State. Tissue samples were tested by the polymerase chain reaction for “Candidatus Liberibacter solanacearum”, the bacterium associated with ZC. Nearly all of these samples were positive for the bacterium. DNA sequence analysis confirmed “Ca. L. solanacearum”. These results provided the first evidence that the zebra chip disease has spread to Oregon and Washington. Oregon and Washington grow approximately 80,000 hectares of potatoes, and therefore ZC poses a significant risk to agriculture in these states.
In August of 2011, potato (Solanum tuberosum) tubers grown in the lower Columbia Basin of southern Washington State and northern Oregon were observed with internal discolorations suggestive of the zebra chip disease (ZC). Symptoms included brown spots, streaks, and stripes in and near the vascular tissue, typical of ZC (1). Symptoms were observed in cultivars Alturas, Russet Norkotah, Pike, Ranger Russet, Umatilla Russet, and Russet Burbank. Foliar symptoms on plants that produced symptomatic tubers included purple discoloration in upper leaves, leafrolling, axial bud elongation, chlorosis, leaf scorch, and wilt. Tissue was taken from two symptomatic tubers each of Alturas and Russet Norkotah, three tubers of Umatilla Russet, and one tuber of Pike. These tubers were tested by polymerase chain reaction (PCR) for “Candidatus Liberibacter solanacearum”, the bacterium associated with ZC (1, 4). Primers specific for the 16S rDNA were CLipoF (4) and OI2c (3), and primers OMB 1482f and 2086r for the outer membrane protein (2). All of these samples, except one Umatilla tuber, were positive for the bacterium. The 16S rDNA and OMB amplicons from one symptomatic tuber each of Alturas (from Washington) and Pike (from Oregon) were cloned and three clones of each were sequenced. BLAST analysis of the consensus sequences confirmed “Ca. L. solanacearum”. The 16S sequences (1,071 bp) from the two tubers were identical and showed 99-100% identity to a number of 16S rDNA sequences of “Ca. L. solanaceaum” in GenBank (e.g. HM246509 and FJ957897). The 16S rDNA sequences were deposited in GenBank as accessions JN848751 and JN848753. Consensus sequences of the two OMB clones (605 bp; deposited in GenBank as accessions JN848752 and JN848754) were identical and showed 97% identity to the two “Ca. L. solanacearum” OMB sequences in GenBank (CP002371 and FJ914617). Potato psyllids (Bactericera cockerelli Sulc), the vector of Ca. Liberibacter solanacearum, were present in ZC-affected fields in Oregon and Washington and the bacterium was confirmed in 5-10% of these insects. Based on foliar and tuber symptoms, specific PCR amplification with two primer pairs, sequence analyses, and the presence of Liberibacter-infected potato psyllids, ZC and “Ca. L. solanacearum” are present in potatoes in Oregon and Washington State. Washington and Oregon together grow ~80,000 hectares of potatoes. ZC has caused significant economic damage to potatoes in Texas, Mexico, Central America, and New Zealand (1). Therefore, ZC may pose a risk to agriculture in Oregon, Washington, and neighboring states. However, the potential for development of widespread and serious disease will depend upon the arrival time and number of infective potato psyllids entering the region.
(1) J.M. Crosslin et al. Plant Health Prog. doi: 10.1094/PHP-2010-0317-01-RV, 2010. (2) J.M. Crosslin et al. Southwest. Entomol. 36:125, 2011. (3) S. Jagoueix et al. Mol. Cell. Probes 10:43, 1996. (4) G.A. Secor, Plant Dis. 93:574, 2009.