Our sunflower plants were responsive to SD treatment for as
little as 1 week at an early developmental stage such as the cotyledon
stage (9 days after sowing) that resulted in accelerated flower
bud initiation as shown by the reduction in the numbers of leaves
and nodes. Similar results were obtained for several other quantitative
SD sunflower cultivars such as ‘Sunrich Pine’ and ‘Fire Cracker’
(data not shown). These results indicate that the juvenile phase of
sunflower is very short. Only a few days of juvenility period is also
described for LD plants Chenopodium (Cumming, 1959) and Brassica
campestris (Friend, 1968). Damann and Lyons (1993) reported
for a LD plant C. lanceolata that days to flower from start of LD
reached the minimum when transferred to LD at the end of juvenility.
In sunflower ‘Sunrich Orange’, the number of days to flower
was shortest when SD treatment was applied from the cotyledon
stage (Table 2). This also suggests its short juvenility period.