Identifcation of candidate type 3 efectors that determine host specifcity associated with emerging Ralstonia pseudosolanacearum strains

Ralstonia pseudosolanacearum (Rps), previously known as R. solanacearum phylotypes I and III is one of the causal agents of bacterial wilt, a devastating disease that afects more than 250 plant species. Emerging Rps strains were identifed infecting new hosts. P824 Rps strain was isolated from blueberry in Florida. Rps strains including PD7123 were isolated from hybrid tea roses in several countries through Europe. P781 is a representative strain of Rps commonly found on mandevilla in Florida. UW757 is a strain isolated from osteospermum plants originating in Guatemala. These strains are phylogenetically closely related and of economic importance on their respective hosts. The objective of this study is to associate the Type 3 Efectors (T3Es) repertoire of these four strains with host specifcity. Candidate T3E associated with host specifcity to blueberry, tea rose, osteospermum, and mandevilla were identifed by sequence homology. Pathogenicity assays on 8 hosts including, blueberry, mandevilla, osteospermum and tea rose with the 4 strains showed that both P824 and PD7123 are pathogenic to blueberry and tea rose. P781 is the only strain pathogenic to mandevilla and P824 is the only strain non-pathogenic to osteospermum. Hypotheses based on correlation of T3E presence/absence and pathogenicity profles identifed 3 candidate virulence and 3 avirulence T3E for host specifcity to blueberry and tea rose. Two
candidate avirulence T3E were identifed for mandevilla, and one candidate virulence for osteospermum. The strategy applied here can be used to reduce the number of host specifcity candidate genes in closely related strains with diferent hosts.