SEED AND POLLEN PRODUCTION AFTER STEM INJECTIONS OF GIBBERELLIN A(4 7) IN FIELD-GROWN SEED ORCHARDS OF PINUS-SYLVESTRIS/

The effects of stem injections of gibberellin A(4/7) (GA(4/7)) were st udied in two experiments conducted in two different field-grown seed o rchards of Pinus sylvestris L. Both experiments were carried out durin g years with favourable conditions for floral induction, i.e., higher temperatures and less precipitation than average years. In experiment 1, cone production and the number of filled seeds per graft increased significantly, the latter by about 60% compared with the control. Fill ed seeds per graft increased in experiment 2 as well, although the inc rease was not statistically significant. In both experiments, GA(4/7) treatment significantly reduced the 1000-seed weight but did not signi ficantly affect the number of filled and empty seeds per cone. In both experiments, grafts stimulated to increase seed production tended to produce smaller cones. In experiment 2, pollen production was signific antly increased after stem injections of GA(4/7). The increase above t he control was about 90%. There was a tendency for stem injections of GA(4/7), which were intended to increase seed production, to reduce po llen production. Clonal effects were significant for all variables tes ted in the study. No damage to the treated grafts were observed that c ould be attributed to the treatment. The use of stem injections of GA( 4/7) as an operational means in seed orchards of P. sylvestris is ther efore recommended.