Infection Patterns of a Liberibacter Associated with Macrohomotoma gladiata, a Psyllid Feeding on Ficus microcarpa

Almost all known Liberibacters can be transmitted by psyllids. This suggests that there is a coevolutionary relationship between these two groups of organisms. However, detailed investigation of Liberibacters and psyllids have often focused on only a few species, thus potentially limiting knowledge on Liberibacter-psyllid associations. This study investigated the infection patterns of a Liberibacter inhabiting Macrohomotoma gladiata, a psyllid species feeding on Ficus microcarpa. Comparison of the Liberibacter's near-full-length 16S rDNA sequence with those of other known Liberibacters revealed that it is closely related to Candidatus Liberibacter asiaticus. A survey of different M. gladiata populations in Taiwan using conventional and quantitative PCR (qPCR) indicated that the Liberibacter could be detected with variable frequencies in all the tested populations; the proportions of individuals carrying large Liberibacter populations also differed depending on the population. Additional analysis of a larger set of samples collected from one specific population revealed that the psyllid's gender and abdominal color were associated with Liberibacter infection density. Significantly greater proportions of individuals with a blue/green abdomen carried high Liberibacter titers. Analysis of the psyllids' body lengths revealed that body size was not affected by Liberibacter infection status and that females, particularly those with an orange abdomen, tended to be larger. The infection patterns of Liberibacter in nymph-infested and nymph-free twigs of F. microcarpa were also determined, and Liberibacter distribution was found to be associated with the presence of nymphs. These findings broaden the understanding of Liberibacter ecology in general and have implications for managing Liberibacter-associated diseases. IMPORTANCE Despite the ever-increasing interest in Liberibacter-psyllid interactions, most of the current knowledge on the subject has been established from studies focusing on species associated with crop diseases. To obtain a more holistic understanding of Liberibacter ecology, we investigated the infection patterns of a Liberibacter recently detected in Macrohomotoma gladiata, a psyllid pest of Ficus microcarpa. We showed that a Liberibacter closely related to Candidatus Liberibacter asiaticus is widely distributed across M. gladiata populations in Taiwan. The study also identified factors associated with the Liberibacter infection patterns, both in M. gladiata and in F. microcarpa. The effects of Liberibacter infection status on psyllid body sizes were also examined. Some of the patterns detected in this work were similar those found in well-known Liberibacters, while some were the opposite. The findings in this work broaden our understanding of Liberibacter ecology in general and may facilitate development of strategies for managing plant diseases.