Current issue: 57(1)
Ethanolic sprays of GA4 or GA7 on 9-year old Scots pine (Pinus sylvestris L.) grafts, repeated four times during the shoot elongation period, resulted in a statistically significant increase in female flowering one year after the treatment. Of the two compounds, GA4 seemed to be somewhat more efficient, yielding 47 female strobili/100 shoots vs. 36 and 6 strobili/100 shoots in GA7 and control treatments respectively. The mixture of GA4 and GA7 compounds was also applied and seemed to have an effect intermediary to those of the pure compounds. However, due to the limited amounts of material, none of the differences between the gibberellins could be statistically confirmed. Male flowering frequencies were also too low to allow any firm conclusions, but the numerical results suggested that the purified gibberellins may promote male and female flowering in different ways.
The PDF includes a summary in Finnish.
Male flowering was studied at the canopy level in 10 silver birch (Betula pendula Roth) stands from 8 localities and 14 downy birch (B. pubescens Ehrh.) stands from 10 localities in Finland in 1963–73. Distribution of cumulative pollen catches was compared to the normal Gaussian distribution. The basis for timing of flowering was the 50% point of the anthesis-fitted normal distribution. To eliminate effects of background pollen, only the central, normally distributed part of the cumulative distribution was used. Development was measured and tested in calendar days, in degree days (> 5°C) and in period units. The count of the parameters began in March 19.
Male flowering in silver birch occurred from late April to late June depending on latitude, and flowering in downy birch took place from early May to early July. The heat sums needed for male flowering varied in downy birch stands latitudinally but there was practically no latitudinal variation in silver birch flowering. The amount of male flowering in stands of the both species were found to have a large annual variation but without any clear periodicity.
The between years pollen catch variation in stands of either birch species did not show any significant latitudinal correlation in contrast to Norway spruce stands. The period unit heat sum gave the most accurate forecast of the timing of flowering for 60% of the silver birch stands and for 78.6% of the downy birch stands. Silver birch seems to have a local inclination for a more fixed flowering date compared to downy birch, which could mean a considerable photoperiodic influence on flowering time of silver birch. The species had different geographical correlations.
Frequent hybridization of the birch species occurs more often in Northern Finland than in more southerly latitudes. The different timing in the flowering causes increasing scatter in flowering times in the north, especially in the case of downy birch. Thus, the change of simultaneous flowering of the species increases northwards due to a more variable climate and higher altitudinal variation. Compared with conifers, the reproduction cycles of the two birch species were found to be well protected from damage by frost.