Archivio Journal of Plant Pathology

Abstract:

‘Candidatus Liberibacter solanacearum’ (CaLsol) is an emerging bacterium, which is seed-borne in carrot (Bertolini et al., 2015). Exclusion of infected seeds is mandatory to prevent the introduction and the establishment of CaLsol in new areas, such as Italy. Here, we tested carrot seeds, sold in Italy during 2015, for CaLsol by analyzing three lots of ‘Berlicum’ (#1, #9 and #17) and one each of ‘Nantese’ (#6), ‘Flakkèe’ (#11), ‘Bolero’ (#3) and ‘Mezza Lunga Nantese’ (#15). DNA was extracted using the QIAGEN DNeasy® Plant mini kit on 0.5 g of seeds ground in CTAB buffer. All samples were analyzed by real-time PCR of the 16S rDNA (Li et al., 2009) and conventional PCR of ISR16/23S (Ravindran et al., 2011) and 50S (Munyaneza et al., 2009) rDNAs. CaLsol DNA was detected, regardless of the method utilized, in all seed lots except ‘Bolero’. Sequence analysis identified two homogeneous groups of CaLsol isolates: I) lots #1, #9, #15 (GenBank accession Nos. KU041863 for ISR16/23S and KU041865 for 50SrDNA), and II) lots #6, #11, #17 (KT984852 for ISR16/23S and KU041864 for 50SrDNA). The single-nucleotide polymorphism analysis revealed that the first group was closely related to the CaLsol haplotype-E (except for having A at nucleotides 1620 and 1632 of ISR16/23S), while the second to the haplotype-D (except for having A at nucleotide 1648 of ISR16/23S, and T at nucleotides 920 and 1068 of 50SrDNA). The detection of CaLsol in different carrot seed cultivars commercialized in Italy highlights the requirement of harmonized and coordinated preventive measures to limit its spread.