Horticulture

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.

AbstractA previously unknown haplotype of the plant pathogen ‘CandidatusLiberibacter solanacearum’ (Lso) was found in cultivated carrots and parsnips in eastern Finland. That same haplotype was found in western Finland, over 300 km away, in the family Polygonaceae, the speciesFallopia convolvulus(wild buckwheat) andPersicaria lapathifolia(pale persicaria) growing as weeds within carrot and parsnip fields. The infected plants, both apiaceous and polygonaceous, showed symptoms of foliar discolouration. This is the first report of Lso bacteria in plants of the family Polygonaceae. The finding that the polygonaceous plants infected with a previously unknown haplotype of Lso were growing among the apiaceous plants infected with Lso haplotype C suggests that these two haplotypes might be transmitted by different vectors. Phylogenetic analyses showed that the new haplotype, called haplotype H, is distinct from the previously characterized haplotypes and appears to have diverged early from their common ancestor. Multi-locus sequence analysis revealed four different sequence types (strains) within the haplotype H. These findings suggest that the haplotype H is likely to be endemic in northern Europe and that the genetic diversity within the Lso species is higher than previously assumed.

Huanglongbing (HLB) or citrus greening disease is the most devastating disease of citrus worldwide. This disease, caused by the bacterium ‘Candidatus Liberibacter asiaticus’ (CLas), leads to low fruit quality and unproductive trees. In 2008, HLB was found in a residential citrus tree in Savannah, Georgia, and, as a result, the state has been quarantined for this disease since 2009. Nonetheless, little is known about the distribution of CLas within Georgia, even though the commercial planting of citrus in Georgia has increased exponentially in recent years. In 2019, 94 samples from commercial and residential citrus trees within 11 counties in coastal and southern Georgia were collected and tested for the presence of CLas. Molecular testing results revealed the presence of CLas in three counties where HLB had not been previously reported and in 9% of samples overall. This is the first definitive report confirming HLB in southern Georgia counties besides those along the coast.

During 2015, samples from 22 apple trees showing proliferation symptoms were collected in southwest Bulgaria and Central and South Poland and tested for phytoplasma presence. ‘Candidatus Phytoplasma mali’ was identified in 18 samples based on results of restriction fragment length polymorphism (RFLP) analysis of the 16S rRNA gene amplified in nested PCR using primer pair P1/P7 followed by R16F2n/R16R2 and F1/B6 primer pairs. The nitroreductase and rhodonase like genes and ribosomal protein genes rpl22 and rps3 were then analyzed using PCR-RFLP technique to study the genetic variability of the  phytoplasma strains. Two restriction profiles, P-I or P-II, were obtained for fragments of 16S rDNA plus 16S-23S spacer region digested with HpaII enzyme. Restriction fragment length polymorphism analysis of nitroreductase and rhodonase like genes using digestion with HincII endonuclease revealed that the all ‘Ca. P. mali’ strains belonged to subtype AP-15. Analysis of rpl22 and rps3 ribosomal protein genes digested with AluI enzyme resulted in classification of detected phytoplasma strains to rpX-A subgroup.