Strobilus Production Research Articles

Promotion of Flowering in the Pinaceae by Gibberellins

AbstractFlowering was significantly promoted in 4‐year‐old grafts of mature coastal Douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) clones by exogenous gibberellins (GAs) A4 and A7 (as a mixture) applied alone and in combination with A5 and A9. Biweekly applications of 400 μg GA4/7 per branch between late March and late June gave a 5‐fold increase in ovulate and 3‐fold increase in staminate strobilus production over untreated controls. 6N‐benzyladenine and 2,3,5‐triiodobenzoic acid applied in combination with GAs had no consistent effect on strobilus production. Non‐destructive branch girdling, ineffective by itself as a cultural treatment, enhanced the GA benefit to flowering. Exogenous application of GA4/7 is effective and appears to be a practical method for promotion of early and enhanced flowering in grafted Douglas‐fir seed orchards.

The relationship between vegetative branch growth and subsequent bearing of megasporangiate strobili in slash pine

Shoot growth of primary branches and subsequent bearing of megasporangiate strobili seem to be relatively independent of each other in slash pine growing in northcentral Florida. Only overall length and diameter at the branch base differed significantly between 44 bearing and nonbearing primary branches measured in 1964. In contrast, a strong relationship appeared between vigor and subsequent production of strobili on 273 secondary branches. The 1963 and 1964 shoots and the terminal buds were longer and thicker on branches which initiated strobili in 1964 than on branches which did not. Bearing secondary branches also had produced more flushes of growth in 1964 than nonbearing ones, and those with the most strobili had been more vigorous than those with few strobili.