Phytoplasma inoculum titre and inoculation timing influence symptomdevelopment in newly infected plants

Previous study unveiled that a single phytoplasma infection may induce mutually distinct symptoms in a single host plant. Four sequentially-developed symptoms were identified in potato purple top (PPT) phytoplasma-infected tomato plants. The symptoms included big bud (BB), cauliflower-like inflorescence (CLI), disrupted sympodial growth patter (DSGP), and witches’ broom growth (WB). In the present study tomato seedling were graft-inoculated at different developmental stages and with PPT phytoplasma inocula of different titres. The results indicated that both phytoplasma inoculum titre and inoculation timing could influence the symptom development in infected plants. Findings from the study support the notion that the type of symptoms in any given shoot is determined by the developmental stage of the shoot apex when it became infected by the phytoplasma.