Articles
ETIOLOGY OF YELLOWS AND WITCHES’ BROOM SYMPTOMS IN SOME ORNAMENTAL PLANTS
The symptoms included general chlorosis, leaf bronzing or reddening and dieback, abnormal production of secondary shoots, upright habit of growth and flower malformation.
The flowers were starile, reduced in size, with virescent petals or necrotic.
Histopathological examination of cross sections showed complete degeneration of the phloem of affected plants.
The disease caused hypertrophy, hyperplasia as well as severe necrosis of phloem cells.
In the ultra-thin sections of the leaves of diseased plants an abundance of pleomorphic phytoplasmas was observed in the sieve tubes of the phloem.
Attempts to transmit a casual agent by grafting on Catharanthus roseus L.G.Don succeeded and resulted in the production of very thin etiolated branches in 2 weeks.
DNA was islated from diseased plants and used for amplification of fragment of phytoplasmas 16S rRNA gene in polymerase chain reaction with universal primers.
A specific product of about 880 bp was obtained from diseased plants of H. bracteatum, providing the evidence of phytoplasma infection.
RFLP analysis of the PCR product was done with restriction enzyme AluI. The pattern obtained in this experiment corresponded to the pattern calculated for American aster yellows (AAY). It suggests that phytoplasmas found in ornamental plants in Poland fall into A-I phylogenetic cluster.