DISTRIBUTION AND MULTIPLICATION OF WESTERN ASTER YELLOWS MYCOPLASMALIKE ORGANISMS IN CATHARANTHUS-ROSEUS AS DETERMINED BY DNA HYBRIDIZATION ANALYSIS

Mycoplasmalike organism (MLO) specific DNA probes derived from chromosomal or plasmid DNA of the severe strain of western aster yellows MLO (SAY) were used to monitor the distribution and multiplication of MLOs in periwinkle plants infected with the SAY or dwarf strain (DAY) of the western AY MLO. Plants were graft-inoculated, and DNA was extracted from different regions of the inoculated plants over a 10-wk period. DNA samples were applied to nitrocellulose membranes and hybridized to cloned, P-32-labeled, MLO-specific DNA probes. Relative concentration and distribution of MLOs were determined by measuring the amount of hybridized probe. Colonization patterns for the two AY-MLO strains were similar. The MLOs were first detected in grafted shoots about 2 wk before symptoms appeared. From the grafted shoots, the MLOs moved into ungrafted shoots, and then systemically throughout the plant. Distribution and concentration of MLOs correlated directly with expression of virescence and proliferation symptoms in aerial portions of the plants. MLO concentrations were highest in symptomatic, actively growing shoots and generally lowest in roots.