Understanding psyllid transmission of Candidatus Liberibacter as a basis for managing huanglongbing

Abstract

Citrus huanglongbing (HLB) represents a major threat to citriculture due to its rapid spread, difficulty of control, severe yield losses, and substantial increases in production costs in HLB-affected orchards. Successful management depends on detailed knowledge of the epidemiology of this disease, which is associated with phloem-limited bacteria of the genus Candidatus Liberibacter that are transmitted by phloem sap-feeding insects known as psyllids (Hemiptera: Psylloidea). Candidatus L. asiaticus (CLas) and the Asian citrus psyllid Diaphorina citri Kuwayama are the major etiological agent and vector, respectively, in the Americas and Asia. This review provides up-to-date information on the relationships of psyllid vectors with Ca. Liberibacter spp. associated with HLB, with emphasis on D. citri and CLas. Knowledge of the transmission mechanisms of these bacteria, as well as aspects of the biology, ecology, and behavior of the vector in relation to the environment, is essential to gain understanding of the HLB epidemics. Such knowledge provides a basis for developing innovative control methods and establishing sustainable management strategies for HLB.

Assessment of Variation in Feeding Behavior by Color Morph in the Asian citrus Psyllid (Diaphorina citri)

“…Although we did not explicitly test color morph influence on CLas transmission, the feeding behavior data presented here can be extrapolated to consider color morph effects based on known associations between vector feeding and the acquisition and inoculation of phloem restricted pathogens (Ebert 2019: Carmo-Souza et al 2020. Since CLas inoculation is related to the frequency and duration of phloem salivation events (Wu et al 2016;Carmo-Sousa et al 2020), the lack of differences detected for the E1 parameter support the hypothesis of no correlation between color morphology and CLas inoculation. Therefore, it is likely that if there are differences in CLas transmission between color morphs, the differences could be attributed to variation in the retention or replication of the bacteria in key organs, such as the salivary glands.…”

“…Phloem access and exploitation is also essential for CLas transmission. Therefore, understanding how color polyphenism influences adult ACP interactions with phloem tissues will provide information about how ACP physiology affects the probability of CLas inoculation (Bonani et al 2010;Luo et al 2015;Wu et al 2016;Killiny et al 2017;Carmo-Sousa et al 2020).…”

Overexpression of a “Candidatus Liberibacter Asiaticus” Effector Gene CaLasSDE115 Contributes to Early Colonization in Citrus sinensis

“…In this study, it was shown that the expression levels of CaLasSDE115 were significantly higher in psyllids compared with those in plants. In the same way in which Bartonella species enter mammalian erythrocytes ( Deng et al, 2018 ), Ca Las cells enter a psyllid’s body by crossing the gut epithelium before subsequently moving to other internal organs and tissues ( Carmo-Sousa et al, 2020 ). Thus, it is suggested that CaLasSDE115 could also be involved in Ca Las’s entry and intracellular movement in the Asian citrus psyllid.…”

Linking Climate Variables to Large-Scale Spatial Pattern and Risk of Citrus Huanglongbing: A Hierarchical Bayesian Modeling Approach

“…Adult psyllids are responsible for the spreading of CLas, whereas, D. citri nymphs are known for greater acquisition efficiency, as well as faster CLas replication (George 2018;Ammar et al 2016;Gottwald 2010). The voluntary and involuntary movement of adult psyllids is associated with wind speed and direction (Carmo-Sousa et al 2020). The mean annual wind speed in MG ranged between 6.19 to 12.8 km/h.…”

“…The extent of HLB throughout Brazilian states can be attributed to the psyllid vectors' capability of short (plant-to-plant and within orchard; 5-320 m) and long-distance (between orchard; ~2.5 km) movement via passive and active strategies, i.e., windassisted dispersal and consecutive short flights, respectively (Carmo-Sousa et al 2020;Antolinez et al 2021). Additionally, the use of infected propagative material through grafting has also been demonstrated to transmit HLB and can thus contribute to the dissemination of the pathogen (van Vuuren & da Graça, 1993).…”