Plant Science

‘Candidatus Liberibacter asiaticus’ (CLas) is an unculturable phloem-restricted α-proteobacterium associated with huanglongbing (HLB). Here, we provide the genome sequence of CLas strain CoFLP1 from its insect vector Diaphorina citri (Hemiptera: Liviidae) collected in the department of La Guajira, Colombia. The CoFLP1 strain is composed of 1,231,639 bp with G+C 36.5% content. This study reports the first CLas genome sequence from Colombia, which will add to CLas genome resources and help to elucidate our understanding of the introduction pathway of HLB in South America.

‘Candidatus Liberibacter asiaticus’, an unculturable α-proteobacterium, is associated with citrus huanglongbing (HLB), a devastating disease threatening citrus production in Brazil and worldwide. In this study, a draft whole-genome sequence of ‘Ca. L. asiaticus’ strain 9PA from a sweet orange (cultivar Pera) tree collected in São Paulo State, Brazil, is reported. The 9PA genome is 1,231,881 bp, including two prophages, with G+C content of 36.7%. This is the first report of a whole-genome sequence of ‘Ca. L. asiaticus’ from Brazil or South America. The 9PA genome sequence will enrich ‘Ca. L. asiaticus’ genome resources and facilitate HLB research and control in Brazil and the world.

Specific scopeThis Standard describes a national regulatory control system for the bacterial pathogen ‘Candidatus Liberibacter solanacearum’ and its vector Bactericera cockerelli when regulated as quarantine pests. It also covers measures to reduce the risk of ‘Ca. L. solanacearum’ spreading to potato production systems when listed as a regulated nonquarantine pest (RNQP) on seed potatoFor the EPPO A1 listed pests recommended for regulation as quarantine pests B. cockerelli and ‘Ca. L. solanacearum’ (Solanaceae haplotypes, i.e. non‐European haplotypes, such as haplotypes A and B), the Standard describes measures to achieve: Exclusion from the EPPO region of B. cockerelli, which is an efficient vector of ‘Ca. L. solanacearum’ within solanaceous crops (e.g. potato, tomato) Eradication of incursions of B. cockerelli Exclusion from the EPPO region of non‐European haplotypes of ‘Ca. L. solanacearum’ Eradication of incursions of non‐European haplotypes of ‘Ca. L. solanacearum’. Although reference will only be made to the non‐European haplotypes A and B, the Standard would also apply to new non‐European haplotypes of ‘Ca. L. solanacearum’ which may have different host ranges or which may be vectored more efficiently by psyllids which are widespread in the region.For the haplotypes which are not recommended for regulation as quarantine pests but are recommended for regulation as RNQPs on seed potato (i.e. European haplotypes, such as C, D and E), the Standard describes measures (specified in Appendix 4) to reduce the risk of spread to potato production systems to achieve: Exclusion of European haplotypes of ‘Ca. L. solanacearum’ from the potato production system Suppression of European haplotypes of ‘Ca. L. solanacearum’ in potato production systems where they are present. Although reference will only be made to haplotypes C, D and E, Appendix 4 would also apply to new European haplotypes of ‘Ca. L. solanacearum’.SpecificapprovalFirst approved in 2017‐09. Revised in 2020‐09.

AbstractCandidatus Liberibacter solanacearum haplotype B (CLsoB) is an economically important pathogen of tomato (Solanum lycopersicum L.) crops in New Zealand and Central and North America. Currently, resistant cultivars of tomato are not available as a management tactic because breeding programmes lack sources of resistance. Therefore, the objective of this study was to identify sources of resistance in tomato to CLsoB. Forty‐six landraces of tomato were collected from several states in Mexico and were inoculated with CLsoB using 20 infested adults of Bactericera cockerelli per plant. Two assays were done over two years under greenhouse conditions. In the first trial, landraces FC22 and FC44 showed a significantly higher proportion of resistant plants, less symptom severity and longer incubation time compared with the other forty‐four landraces and two susceptible cultivars. In the second assay, resistance to CLsoB of the landraces FC22 and FC44 was confirmed because they had again significantly greater numbers of resistant plants, less symptom severity, relative lower CLsoB titers and longer incubation time relative to the other genotypes. All plants considered resistant from both assays had DNA of CLsoB. Results indicate that all resistant plants from these landraces are promising sources for the development of tomato cultivars with resistance to CLsoB.