Differences in Zebra Chip Severity between "Candidatus Liberibacter Solanacearum' Haplotypes in Texas
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2018, The Potato Association of America. Candidatus Liberibacter solanacearum (Lso) is a phloem-restricted plant pathogen that is vectored between host plants by the potato psyllid, Bactericera cockerelli. Lso infects solanaceous crops whithin North America and New Zealand and is responsible for causing zebra chip (ZC) in potato. Two Lso haplotypes (A and B) have been identified infecting potato (Solanum tuberosum). Previously, we identified differences in disease severity associated with each Lso haplotype in tomato (Solanum lycopersicum). In this study, the severity of ZC symptoms was evaluated for Lso haplotypes A and B independently or in co-infection in Atlantic variety potato tubers grown in Texas fields. Discolorations in tuber vascular tissues were measured in potato chips using a published 6-point visual scale and compared among plants submitted to five treatments: no psyllids (control), psyllids not infected with Lso (LsoFree), psyllids infected with Lso haplotype A (LsoA), psyllids infected with Lso haplotype B (LsoB), and psyllids infected with both haplotypes (LsoAB). These experiments were performed a total of three times, twice in the Lower Rio Grande Valley (Weslaco, TX) during the winters 2014 and 2018 and once during the spring 2015 in the Texas Panhandle (Springlake, TX). This study showed that significantly lower ZC symptom severity was associated with plants treated with LsoA-infected psyllids compared to plants treated with either LsoB- or LsoAB-infected psyllids; however, this difference was marginal. This difference might be relevant for the disease biology; it has no impact on the tuber suitability for the market. This study also showed that average tuber mass was significantly lower in plants infected with Lso compared with uninfected plants and that this reduction in mass was similar among Lso haplotype treatments. Overall, this study demonstrates that Lso haplotypes A and B cause slightly different ZC symptom severity and that ZC symptom severity in plants treated with psyllids co-infected with both haplotypes is similar to the symptoms associated with Lso haplotype B.
