Green gladiolus flowers: phytoplasma presence and identification

The presence and identity of phytoplasmas infecting gladiolus plants sold as a green cultivar were obtained by PCR and RFLP analyses of the 16S ribosomal (r) RNA gene and other phytoplasma genes. Ten gladiolus corms were planted in pots under insect proof conditions. Nine corms sprouted normally while one corm produced two shoots. Plants were somewhat stunted although vegetation was without malformation or chlorosis. However, no flower production was observed in any of the plants. Total DNA was extracted from corms, leaves and second-generation corms. Phytoplasma DNA was amplified by nested-PCR on the 16S rRNA gene using several nested systems and phytoplasmas of four ribosomal subgroups (16SrII, -IX, -X and -XII) were detected, generally in mixed infections. Phytoplasma identification by direct amplicon sequencing followed by Blast analysis allowed identification of ‘Candidatus Phytoplasma prunorum’ and ‘Ca. P. phoenicium’-related strains. These results were confirmed by nested PCR amplification on secA, leuS and rp genes. The cormlets were infected only by phytoplasmas in the 16SrII group. Detection of phytoplasmas in non-flowering plants suggests that the original corms were likely collected from plants producing green flowers following visual selection. The “appealing” and unusual green flower colour was considered as a new gladiolus cultivar and used for commercial purposes. The two-season cultivation reduced the mixed phytoplasma infections to the presence of phytoplasmas of only one ribosomal group (16SrII); however, the infected plants were of no commercial value.