Pour la première fois, toutes les étapes de la micropropagation de l'érable à sucre (Acer saccharum Marsh.) ont été complétées avec succès. Les bourgeons de plus de 200 plants d'érable à sucre âgés de 2 ans ont été débarrassés de leurs écailles et mis en culture sur un milieu contenant les sels de Murashige et Skoog ainsi que les éléments organiques de Bourgin et Nitsch, tous dilués au tiers, avec ou sans régulateur de croissance. Le taux de survie des explants en fin d'induction a été supérieur sur un milieu sans régulateur de croissance. La formation de tigelles et la multiplication ont été accomplies sur les mêmes milieux additionnés de 0,01 ou 0,025 mg·L -1 de thidiazuron ainsi que du 6-(γ γ , -diméthylallylamino)purine, du 6-(γ γ , -diméthylallylamino)purine riboside ou de l'acide phénylacétique (APA). Les tigelles se sont allongées sur des milieux contenant 0,3 mg·L -1 d'APA et l'induction racinaire a été réalisée sur des milieux contenant 0,3 mg·L -1 d'APA en présence d'acide naphtalène-acétique. Quelques tigelles se sont enracinées lorsque transférées dans de la vermiculite. Bien que le taux de réussite soit faible, des tiges enracinées ont été produites par la multiplication de bourgeons.Abstract: For the first time, all stages required for the micropropagation of sugar maple (Acer saccharum Marsh.) have been successfully completed. Buds of more than 200 seedlings of two-year-old sugar maple trees were stripped of their scales and cultured on media containing Murashige and Skoog salts with Bourgin and Nitsch organic elements, all diluted to 33%, with or without growth regulator. Survival rate after induction was higher in media without growth regulator. Stem formation and multiplication succeeded in media of the same composition but containing 0.01 or 0.025 mg·L -1 thidiazuron, as well as 6-(γ γ , -dimethylallylamino)purine, 6-(γ γ , -dimethylallylamino)purine riboside, or phenylacetic acid (PAA). Stem elongation took place in media with 0.3 mg·L -1 PAA. Root induction was achieved in media containing 0.3 mg·L -1 PAA with naphthaleneacetic acid. A few shoots rooted when transferred into vermiculite. Although the overall rate of success is still low, rooted shoots were produced by bud multiplication.Brassard et al. 690
[859][860][861][862][863][864][865][866][867]. The objective of this study was to define the optimum period for collecting sugar maple (Acer saccharum Marsh.) stem cuttings. In 1999 and 2000, shoot development was monitored on young trees from a plantation established in 1993. Stem base water content and the number of pairs of terminal bud scales changed over time, reflecting meteorological characteristics of both years. In 1999, rooting percentage was high regardless of collection date, within a 7-wk period. The 2000 rooting trial covered a longer time frame and identified an optimal window during which rooting percentages reached 60 to 83%. Rooting success dropped below 30% for cuttings harvested too early or too late. Thus the optimal time for collecting sugar maple cuttings spans several weeks, but with significant year-to-year variations. For both years, optimal rooting was associated with a stem base water content lower than 75% but higher than 55%, and with the presence of one to three pairs of apical bud scales. This stage is reached when at least 270 degree-days above 5°C are accumulated. Using these indicators, practitioners can consider local conditions and year-to-year climatic variations to harvest sugar maple cuttings at an optimum stage of development.
Cuttings were taken at different levels in the crown of both flower-bearing and sexually immature 9-year-old black spruce seedlings (Piceamariana (Mill.) B.S.P.). We obtained satisfactory rooting success, despite the relatively old age of the trees. The rooting percentage of the cuttings taken from the lower third of the crown was significantly higher (p < 0.01) than that of the cuttings originating from the middle and top thirds of the crown (53%, 36%, and 29%, respectively). Cuttings from the upper portion of the crown showed persistent signs of advanced maturation, while those from the bottom of the crown regained an almost juvenile appearance after rooting. Surprisingly, the cuttings taken on flower-bearing trees rooted better (p < 0.10) than those taken on sexually immature trees (48% vs. 30%). Large and significant differences were also recorded between individuals of both groups. No significant interaction was found between sexual maturity and crown position of the cuttings for rooting percentage. The effects of maturation on the rate of rooting and the relevance of replacing grafting by rooting for certain purposes are discussed.
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