Development of the female cone of Pinus radiata D. Don
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Material of two clones of Pinus radiata (19 and 55), harvested from a seed orchard at Kaingaroa, at intervals of 1-4 weeks was studied. The same clones and some others were harvested less frequently from Whakarewarewa. Dissection and counts of terminal shoot components for each harvest confirmed that, as in other species of Pinus, female cones are initiated in summer. Cones emerge from their bud scales prior to pollen shed in early spring. Pollination drops are produced by different ovules throughout the cone's receptive period. One ovule can produce a drop on more than one occasion. In a simulated drop, pollen floats through the fluid with its wings upward. Pollen treated with chloroform does not float, but still reaches ovule micropyles when applied to bagged cones. An electron microscope study of receptive ovules showed that the most active cells were the nucellus cap cells, some of which develop vacuoles and collapse. Commencement of pollen shed varies with year. Duration at Whaka. (1972) was five weeks, but the timing of clonal receptivity varies. Receptive duration of cones varied from 3 to 13 days, depending on weather, and for bagged cones was shorter than for unbagged cones. Highly significant year to year differences in the amount of pollen trapped were shown. Counts showed a highly significant difference between clones in the amount of pollen in ovule micropyles. P. radiata ovules develop like other pinus ovules, but the duration of developmental phases is longer. A band of elongated thick-walled cells connecting the ovule and the scale vascular tissue differentiates by fertilization. Causes and frequency of ovule loss are described, along with other factors affecting seed production, (total scale number, potential seeds, fertilization failure and embryo breakdown). Clone 55 produces fewer seeds per cone than clone 19, but accommodates more archegonia and pollen. It has fewer unpollinated ovules, but more pollinated ovules abort. Year and site differences also affect seed yield per cone.