Agronomy and Crop Science

‘Candidatus Liberibacter asiaticus’ is an insect-transmitted, phloem-restricted α-proteobacterium associated with huanglongbing. Here, we provide the whole genome sequence of ‘Ca. L. asiaticus’ strain ReuSP1 from its insect vector Diaphorina citri (Hemiptera: Liviidae) collected in La Réunion. The genome is composed of 1,230,064 bp and has a 36.5% G+C content. This study reports the first ‘Ca. L. asiaticus’ genome sequence from La Réunion, which will add to ‘Ca. L. asiaticus’ genome resources and help elucidate our understanding of the introduction pathway into La Réunion.

‘Candidatus Liberibacter asiaticus,’ an uncultured α-proteobacterium, is associated with citrus huanglongbing (HLB, yellow shoot disease), a destructive disease threatening citrus production worldwide. Here, we reported the draft genome sequence of ‘Ca. L. asiaticus’ strain Myan16 from an HLB-affected lime tree in Myitkyina, Kachin State, Myanmar. The strain Myan16 genome is 1,229,102 bp with an average G+C content of 36.4%, along with a circular prophage: P-Myan16-2 (36,303 bp, type 2). This is the first genome sequence of a ‘Ca. L. asiaticus’ strain from Myanmar, which will enrich the current ‘Ca. L. asiaticus’ genome sequence database and facilitate HLB epidemiology research in Asia and world.

Abstract“Huanglongbing” (HLB) is one of the most devastating diseases of citrus orchards worldwide. Samples from 183 citrus plants of different cultivars and rootstock/cultivar combinations, showing HLB symptoms in three Caribbean countries (Cuba, Jamaica, and Guadeloupe-France), were collected to verify the possible co-infection of ‘Candidatus Phytoplasma’ and ‘Candidatus Liberibacter’ species. The 64% of the samples resulted positive to the ‘Ca. L. asiaticus’ and the 27% to diverse ‘Ca. Phytoplasma’-related species, moreover about the 14% of the samples infected with ‘Ca. Liberibacter’ were also found positive to phytoplasmas, indicating the presence of mixed infection especially in the orchards located in Cuba. Moreover, in one of the samples from Jamaica mixed phytoplasma infection was detected. Moreover the detection of only phytoplasmas in 11 symptomatic citrus samples collected from Cuba and Guadeloupe without ‘Ca. Liberibacter’ detection, confirmed that the symptomatology cannot be the sole criterium to discriminate between the presence of the two pathogens, and molecular detection is necessary to identify single or mixed infections. Diaphorina citri insects collected from Cuba and Guadeloupe resulted infected with ‘Ca. L. asiaticus’ confirming its active role in the dissemination of the pathogen. Only one insect of the Cicadidae family, collected in Guadeloupe, was found positive for phytoplasma presence. Considering that the phytoplasmas belonging to some ‘Candidatus species’ were detected in the three countries in different citrus varieties, a relevant role as phytoplasma reservoir can be attribute to citrus orchards.

AbstractThe olive fruit fly, Bactrocera oleae, the most serious pest of olives, requires the endosymbiotic bacteria Candidatus Erwinia dacicola in order to complete its development in unripe green olives. Hence a better understanding of the symbiosis of Ca. E. dacicola and its insect host may lead to new strategies for reduction of B. oleae and thus minimize its economic impact on olive production. Studies of this symbiosis are hampered as the bacterium cannot be grown in vitro and the established B. oleae laboratory populations, raised on artificial diets, are devoid of this bacterium. Here, we sought to develop a method to transfer the bacteria from wild samples to laboratory populations. We tested several strategies. Cohabitation of flies from the field with the laboratory line did not result in a stable transfer of bacteria. We provided the bacteria directly to the egg and also in the food of the larvae but neither approach was successful. However, a robust method for transfer of Ca. E. dacicola from wild larvae or adults to uninfected flies by transplantation to females was established. Single female lines were set up and the bacteria were successfully transmitted for at least three generations. These results open up the possibilities to study the interaction between the symbiont and the host under controlled conditions, in view of both understanding the molecular underpinnings of an exciting, unique in nature symbiotic relationship, as well as developing novel, innovative control approaches.