Abstract
The effect of short (8 h), natural (11·5 to 12·5 h) and long (18 h) days on the growth and development of whole plants and rooted leaves of sweet potato (Ipomoea balatas) were studied. In whole plants long days increased branch length, reduced branch number, delayed senescence and promoted leaf expansion. The increased shoot growth in response to long days was associated with reduced tuber yield. Tuber yield was greatest in plants given natural days, although in this treatment shoot growth was intermediate to that in the other two daylengths. Long days were inhibitory to flowering. Rooted leaves appeared insensitive to changes in daylength. It is suggested that the effect of daylength on whole plants may be related to changes in endogenous hormone levels, particularly that of gibberellin, and that the lack of effect on rooted leaves may be due to the inability of the phytomodels to perceive the photoperiodic stimulus and reduced capacity for gibberellin synthesis.
