The Abortion of Conelets in Pinus Radiata

Observations and records collected over a six-year period show that, in a seed orchard of Pinus radiata at Kaingaroa Forest, approximately half of all female strobili initiated abort during the first year after pollination. For an average clone this process of conelet drop starts at the time of receptivity, reaches a peak some four to six weeks later, and then decreases in intensity. This time sequence differs somewhat in individual clones. By four months after pollination the process has effectively stopped and very few conelets drop subsequently. There are significant differences between clones in the percentage of strobili which abort; this factor appears to be in part correlated with differences in growth rate, but it is unlikely that all the clonal variation in conelet drop is explicable in these terms. The amount of conelet drop occurring is effectively the same after both open and controlled pollinations. Within a tree there is some indication that the percentage of strobili dropping is greater in the lower part of the crown than in the upper part.