The effect of gibberellins on flowering in roses

The gibberellins A(1), A(3), A(5), A(8), A(19), A(20), and A(29) were ident ified in vegetative shoot tips of Rosa canina by comparing their mass spect ra and Kovats retention indices with those of standards. Most wild roses ha ve a shea, flowering season of 2-4 weeks in spring, whereas most modern cul tivars flower recurrently. 'Felicite et Perpetue' is a short-season hybrid from a cross between a wild rose and a recurrent-flowering rose, whereas it s sport, 'Little White Pet,' flowers recurrently. The concentrations of gib berellins (GAs) were measured in shoot apices of both cultivars. In March ( before floral initiation in spring) the concentrations of GA(1) and GA(3) w ere respectively threefold and twofold higher in 'Felicite et Perpetue' tha n in 'Little White Pet.' In April (after floral initiation) the concentrati ons of both gibberellins were substantially greater than in March, and conc entrations of GA(1) and GA(3) were, respectively, 17-fold and 12-fold: grea ter in 'Felicite et Perpetue' than in 'Little White Pet.' It is postulated that, in 'Felicite et Perpetue,' floral initiation occurs when concentratio ns of GAs are low and is inhibited when concentrations of GAs are high, whe reas in 'Little White Pet' concentrations of GAs remain at permissive level s throughout the growing season. Applications of GA(1) and GA(3) to axillar y shoots in March inhibited floral development in 'Felicite et Perpetue' bu t not in 'Little White Pet.' This suggests that the combined concentration of exogenous and endogenous gibberellins might have been raised to inhibito ry levels in the former but not in the latter cultivar.