A method was developed for estimating the frequency of hybrids in the
seed crop of a multiclonal hybrid larch seed orchard using isozyme gen
etic markers. The technique was used to monitor the output of a commer
cial hybrid larch seed orchard. Among the seeds collected from Europea
n larch clones, some 65 per cent were hybrid, compared with 19 per cen
t from Japanese larch clones. Unequal reproductive effort and differen
ces in flowering time between the two parental species may account for
the results. Possible application of these techniques for the certifi
cation of seed and planting stock are discussed.