Effects of ‘Candidatus Liberibacter Solanacearum’ Haplotype on Atlantic Potato Tuber Emergence Rate in South Texas

The bacterium ‘Candidatus Liberibacter solanacearum’ (Lso) is a phloem-restricted plant pathogen associated with different diseases worldwide. In North America, two haplotypes, LsoA and LsoB, are vectored by the potato psyllid, Bactericera cockerelli Sulc that causes zebra chip (ZC) in potato (Solanum tuberosum L.) and other solanaceous plants. In potato, both haplotypes cause similar symptoms albeit with different severities: LsoB-infected potato plants exhibit more severe ZC tuber symptoms compared to LsoA-infected plants. Previous research suggested that Lso-infected plants could produce viable seed tubers, potentially creating a reservoir for Lso propagation. The current study evaluated the effect of Lso haplotype on the emergence rate of tubers produced by infected potato plants (var. ‘Atlantic’) grown in the Lower Rio Grande area during the 2018 and 2019 growing seasons. Five Lso treatments were evaluated: uninfested controls, plants infested with uninfected psyllids (LsoFree), plants infested with LsoA- or LsoB-infected psyllids (LsoA and LsoB, respectively), and plants infested with psyllids co-infected with both Lso haplotypes (LsoAB). A portion of harvested tubers were evaluated for ZC symptom severity using a visual score. The remaining tubers were placed in cold storage for six months and then used as seed tubers to compare emergence and plant development rates among the treatments. This study confirms the previously reported differences in ZC symptom severity between Lso haplotypes. Furthermore, this study showed that tubers produced by Lso-infected plants were 90.1 ± 8.2% inviable. Importantly, all plants developing from these seed tubers tested negative for the presence of Lso. The results of this study suggest that while seed tubers produced by Lso-infected plants can germinate, the daughter plant was not infected by Lso. Therefore, Atlantic tubers produced by previously infected plants with Lso haplotypes A and B in South Texas do not represent a reservoir for Lso disease.