Search

Two injections of 50 mg of gibberellin A4/7 (GA4/7) into the trunk base of 27-year-old black spruce, Picea mariana (Mill.) BSP, during rapid vegetative shoot elongation gave a fourfold significant increase of seed cone production in the following year compared with controls. Treated trees produced a mean number of 309 ± 28 SE cones versus 57 ± 7 and 83 ± 10 produced by untreated trees and by control trees injected with 95% ethanol (the solvent used), respectively. A similar increase was reflected in the mean total weight per tree of nearly mature cones. It is shown that GA4/7 was able to induce additional cone buds during a very heavy cone crop. Potential effects of gibberellin treatments on phytophagous insects are discussed. Resume : Les auteurs dOmontrent lieffet de deux injections de 50 mg de gibbOrelline A4/7 (GA4/7) ‡ la base du tronc diOpinettes noires, Picea mariana (Mill.) BSP, ‚gOes de 27 ans durant la phase diOlongation rapide de la pousse terminale. Comparativement aux traitements tOmoins, ces injections ont provoquO une augmentation significative par un facteur de quatre de la production de cUnes de semences liannOe suivante. Les arbres traitOs affichaient un production moyenne de 309 ± 28 ES cUnes comparativement ‡ 57 ± 7e t 83 ±10 pour les arbres tOmoins et ceux injectOs ‡ liOthanol ‡ 95% (le solvant utilisO), respectivement. Une augmentation similaire a OtO observOe quant au poids total moyen de cUnes presque matures par arbre. Les auteurs ont Ogalement dOmontrO que lihormone GA4/7 pouvait induire une plus grande production de bourgeons ‡ cUnes durant une trs bonne annOe semencire. Les effets potentiels des traitements ‡ la gibbOrelline sur les insectes phytophages sont discutOs. (Traduit par la ROdaction)

Potted 5-year-old grafts of black spruce (Piceamariana (Mill.) B.S.P.) growing in either a heated greenhouse or an outdoor holding area were sprayed weekly at 200 mg•L−1 gibberellin A4/7 for various durations and timings. The application began 1 to 6 weeks after vegetative bud break and continued until the end of lateral shoot elongation. Sprayings ended at the same time for all treatments, about 1 week before leaf primordial differentiation on the shoot apices. The best response in seed-cone production occurred when application began 2 weeks after bud break (midstage of rapid shoot elongation) and continued for 5 weeks; treatments were also effective when applications began 3 weeks after bud break or earlier and continued for 4 to 6 weeks. Treatments initiated later (4 to 6 weeks after bud break) were not effective. Grafts kept outdoors produced more seed cones than those kept indoors. The effects on cone production of gibberellin A4/7 application at four different concentrations were compared by spraying for 6 weeks, beginning 1 week after vegetative bud burst. Gibberellin A4/7 at 200 mg•L−1 was the lowest foliar spray concentration found to be effective in promoting seed-cone production.

In western hemlock (Tsugaheterophylla (Raf.) Sarg.), the number of microstrobili per shoot averages 4.2. Each microstrobilus averages 13.9 bud scales and 17.2 microsporophylls. Microsporangia have a transverse dehiscence layer on the abaxial surface. There are an average of 1476 pollen grains per microsporangium and 17.4 million pollen grains per gram.Meiosis begins in the fall but stops at pachytene in November; it resumes in the middle of February and is completed in 1 week. Three weeks after the completion of meiosis the first prothallial cell forms and two weeks later the pollen grains reach maturity. Pollen shedding occurs 1.5 months after the resumption of meiosis and lasts for 2 weeks. Chromosome behavior and pollen formation are normal in 98.4% of the cells and in 99.7% of the pollen grains. The common abnormalities encountered are chiasma bridges, precocious disjunction, lagging chromosomes, and undersized pollen grains. The abnormalities may be attributed to the low temperatures occurring during meiosis and pollen development.

Black spruce (Piceamariana (Mill.) B.S.P.) grafts growing in a seed orchard were sprayed with gibberellin A4/7, and grafts and trees in families growing in arboreta were sprayed with gibberellin A4/7 and (or) vitamin E from vegetative bud burst to the end of shoot elongation. Gibberellin A4/7 was very effective in promoting seed cones and 400 mg/L appeared optimal. Vitamin E at 1000 mg/L was not effective. Vegetative bud burst occurred in mid-May and shoot elongation ended in late June. Needle primordia were visible on the apices of newly formed buds at the end of June. Reproductive buds had fewer bud scales than vegetative buds. It appeared that potential reproductive buds terminated their bud scale initiation earlier. Gibberellin A4/7 application to promote seed-cone production should be carried out before bud-type differentiation. This coincides with the end of lateral shoot elongation.

Repeated pollinations with brush had very little effect on the production of filled seed and pollen from the first pollination was most likely to accomplish fertilization in white spruce (Piceaglauca (Moench) Voss). Based on the filled seed and the number of coloured pollen on the nucellus, it was suggested that pollinated ovules would stop exuding any pollination drops.

In Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), microstrobilate size increases acropetally along the shoot. Microstrobili have an average of 64.5 microsporophylls and 27.3 bud scales. Microsporangia have an oblique-transverse dehiscence layer on the abaxial surface. There are 462 pollen grains per microsporangium and about 3 million pollen grains per gram.