Tanemura and Kurashima (2004) reported that in 20 of 23 sunflower
cultivars used SD treatment beginning at the fourth leaf
stage accelerated flowering and reduced stem length; however,
these investigators did not examine the effect of the number of SD
cycles on flowering and flower quality. Damann and Lyons (1993)
studied the effect of the number of inductive LD cycles on flowering
with a LD plant Coreopsis lanceolata, and demonstrated that limited
inductive photoperiod (i.e. LD cycle number) inhibited stem elongation
of ‘Early Sunrise’ plants along with slightly late flowering. In
a facultative (or quantitative) SD plant celosia, timing, not but duration,
of inductive SD treatment beginning after the development of
1–5 nodes impacted node number below the terminal inflorescence
(Warner, 2009). Delaying the beginning of SD treatment increased
node and leaf number below the terminal inflorescence, however,
flowering was still accelerated compared with plants grown under
constant LD. When photoperiod treatment was started immediately
after germination, the duration of SD treatment interacted
with timing of SD treatment and cultivar to impact node number
below the terminal inflorescence. These results indicate variability
in impacts of the number of photoinductive cycles on flowering
and reproductive development across photoperiodic plant species,
cultivars and developmental stages.