Acquisition dynamics of ‘Candidatus Liberibacter asiaticus’ and ‘Ca. L. americanus’ by Diaphorina citri highlights the epidemiological decline of ‘Ca. L. americanus’

Huanglongbing (HLB) disease in Brazilian citrus orchards is historically associated with ‘ Candidatus Liberibacter americanus’ ( C Lam), which occurs exclusively in Brazil, and the cosmopolitan ‘ Ca. L. asiaticus’ ( C Las), both vectored by Diaphorina citri . When HLB was first reported in 2004, both species were detected, with C Lam predominating and of wider spatial distribution. However, from 2008 onward, C Las became dominant, and C Lam was barely detected after 2013. To investigate this shift and decline on C Lam incidence, we examined the acquisition by D. citri of C Lam, C Las, or both, from single-infected or co-infected symptomatic citrus plants, as well as during the incubation period. Acquisition incidence of C Las reached 100% from the fifth nymphal stage onward, whereas C Lam acquisition plateau of 80% was achieved at 40 days after adult emergence, suggesting delayed psyllid infection. During the incubation period, C Las was acquired in 86% of D. citri individuals, compared with 10% average for C Lam. C Las titer in D. citri was up to two and half-fold higher than C Lam titer. Consistently, C Lam was also associated with later infection of citrus flushes compared to C Las. Altogether, our findings provide experimental evidence that the shift in C Las over C Lam in Brazilian citrus belt results from faster infection of sweet orange flushes and higher infection rates and higher bacterium titer in D. citri .