Relative Effectiveness of Different Gibberellins in the Induction of Parthenocarpic Development in Rosa

GIBBERELLIC acid (gibberellin A 3 ) has been shown to be active in setting parthenocarpic fruit in Rosa 1,2 . The relative activity of gibberellins A 1 , A 3 , A 4 , A 5 , A 8 and A 9 in this respect was determined in April 1962 with two clones of R. spinosissima growing in a cool greenhouse, by cutting off the ‘disk’ (carrying with it the calyx, corolla, stamens and stigmas) from unopened flower-buds and applying the gibberellins in 1 µl. of 25 per cent ethanol to the cut surface. This gave better results than injecting the solution into the cavity of the receptacle. Controls, in which ethanol alone was used, abscissed within 2 weeks. An average of c . 15 buds (with individual tags) was used for each treatment and their growth in diameter was compared with that of a sample of 104 normal buds, by measurement at 2-weekly intervals. With A 3 , quantities ranging from 0.01 to 10 µg per bud were used: with the other gibberellins, 0.1 and 1.0 µg per bud.