Simultaneous evaluation of ‘Candidatus Phytoplasma’ and ‘Candidatus Liberibacter solanacearum’ seed transmission in carrot

Abstract

Analysis on commercial carrot seeds and derived plants were performed to evaluate the ‘Candidatus Liberibacter solanacearum’ and ‘Candidatus Phytoplasma’ presence. The analyses on the seeds demonstrated the presence of both prokaryotes in nearly 100% of the seed batches tested. Sequencing confirmed that ‘Ca. L. solanacearum’ strains detected in the seed samples belong to the haplotype D. Seedlings were grown in an insect proof greenhouse and in a growing chamber under controlled conditions. Symptoms of root malformation and leaf whitening and browning were observed in some of the carrot plants obtained from seed. DNA extraction and PCR assays were performed on both symptomatic and asymptomatic samples and diverse ‘Candidatus Phytoplasma’ species were detected in the seedlings at different growth stages. DNA belonging to the ribosomal groups 16SrI and 16SrXII-A was detected and confirmed by RFLP analysis and sequencing indicating the seed transmission of these phytoplasmas in carrot. The analyses to detect ‘Ca. L. solanacearum’ in these seedlings resulted always negative.