Characterization of juvenility and photoperiodic responses of Rudbeckia hirta originating from different latitudes

Rudbeckia hirta is a tender perennial or self-sowing annual which is becoming increasingly popular as a garden flower and a component of wildflower meadow mixes. It may also have -considerable potential for use as a potted crop. R. hirta has a defined juvenility period but preliminary unpublished results suggested that plants originating from different latitudes may possess unequal juvenile periods and exhibit dissimilar sensitivities to photoperiod. Seven R. hirta ecotypes originating from latitudes ranging from 30.l0oN to 45.l0oN were exposed to long days (LD) at different leaf numbers to determine juvenile phase length and speed of floral initiation. Ecotypes from northern latitudes had fewer leaves at maturity and, overall, there was a quadratic relationship between latitude of origin and number of days to first flower from start of LD. Once plants were mature, the speed of floral initiation and development also varied among ecotypes.