Transmission dynamics of Candidatus liberibacter solanacearum halotypes A and B by potato psyllid nymphs: Bioassay and transcriptomic insights

'Candidatus Liberibacter solanacearum' (Lso) is a bacterial plant pathogen transmitted by psyllids. Several Lso haplotypes have been reported worldwide. Among them, LsoA and LsoB are transmitted by the potato psyllid, Bactericera cockerelli, and infect solanaceous crops in the United States. The transmission of these haplotypes by adult psyllids was previously evaluated. However, fewer data are available on their transmission by psyllid nymphs. To address this knowledge gap, we investigated the transmission of these two Lso haplotypes by psyllid nymphs. Our aim was to determine if nymphs transmitted these haplotypes at different rates and determine the implication for disease epidemiology. First, we quantified LsoA and LsoB titers in third-instar nymphs after 1-, 5, and 7-day short acquisition access period (AAP) and of third- and fifth-instar potato psyllid nymphs from infected psyllid colonies (two long acquisition periods). Second, we evaluated the transmission efficiency of LsoA and LsoB by third-instar nymphs to tomato plants. Third, we conducted a transcriptomic analysis of nymph guts after 1- and 5-day AAP. We found accumulation differences between the Lso haplotypes depending on the assessed life stage and the length of the AAP. We also discovered that LsoA was transmitted earlier and with higher efficiency by nymphs than LsoB. Our transcriptomic analyses identified differences in the psyllid response to each haplotype that could explain the observed accumulation and transmission results. Our findings provide valuable insights into the transmission dynamics of these two Lso haplotypes by nymphal vectors, shedding light on the epidemiology of the disease they cause.