The phytoplasma-mediated witches’ broom disease in Parthenium hysterophorus L., a notorious weed, inhibits flower formation and percentage of seed setting. Even the seeds produced from infected plants showed poor viability and reduced rate of germination. Expression analysis of three orthologous genes in P. hysterophorus, namely, APETALA-1 (PhAP1), ubiquitin binding protein (PhDA1), and RING-type E3 ubiquitin ligase (PhATL80) showed significant variation in their transcription levels. Expression of PhAP1, PhDA1, and PhATL80 was higher in apical shoot bud and inflorescence than in other studied tissues. Infected plants showed suppressed expression of PhAP1 and PhATL80 in the inflorescences while no significant variation was observed in PhDA1 expression. This resulted in floral to vegetative transition, causing phyllody and virescence, and lesser seed setting.

These findings suggest that in naturally phytoplasma-infected P. hysterophorus, expression of gene(s) participating in floral development as well as seed setting at onset of the reproductive phase is suppressed.