Characterization of Basal-Defense Resistance in Potato Genotypes to Zebra Chip (Candidatus Liberibacter solanacearum).

Zebra Chip (ZC) is a destructive disease in commercial potato (Solanum tuberosum ) production. The disease is associated with a phloem-limited and uncultivable bacterium, ‘Candidatus Liberibacter solanacearum (Lso)’. The pathogen is transmitted by the potato psyllid [Bactericera (Paratrioza) cockerelli Sulc]. Due to its invasiveness, ZC has become a major threat to the potato industries in US and other potato production regions over the world. Currently, no commercial potato cultivar has been found resistant to ZC. As ‘Ca. Liberibacter asiaticus’, Lso also encodes a flagellin with a highly conserved domain of 22 amino acids (flg22_Lso) near the N-terminus. As a pathogen- associated molecular pattern (PAMP), the flagellin may trigger a basal defense resistance that is often associated with Reactive Oxygen Species (ROS) in potato plants. One hundred eight genotypes of potatoes were tested for ROS activity using the flg22_Las and flg22_Lso, respectively. Four of them had ROS activity over 20-folds more than the other genotypes. Moreover, the expression of several representative genes involved in innate immunity was transiently up-regulated by the fla_Lso via Agrobacterium-mediated transient expression. It is worth noting that the expression of Flagellin-sensing 2 gene (StFLS2) was up regulated differently in selected potato genotypes. We further revealed the StFLS2 from these three potato genotypes had different number of Leucine-rich repeats and mutation in putative important amino acids. Further characterization of the PAMP-triggered immunity on the selected potato genotypes may provide new insights into Liberibacter-infected disease complex.