A Novel Gel-based Method for Isolation of Stigmas During Controlled Pollination Experiments

In forestry, controlled pollination (CP) allows the combining of genetic material of selected elite trees to produce high quality, and consequently high value, seed. The aim of the present study was to develop a novel isolation method that would allow the technique to be conducted without expensive and time-consuming bagging, making CPs on small-flowered eucalypts commercially viable. We compared the current method of isolating inflorescences using exclusion bags to a novel method which uses sodium alginate gel. Sodium alginate was effective in keeping external pollen away from the stigma, since no seed was produced in those treatments that were not manually pollinated but isolated in this way. In addition, flowers hand-pollinated and isolated with sodium alginate produced progeny that were 100% outcrossed with the applied pollen. The exclusion bags, on the other hand, were not as effective in protecting the stigma as seed was produced in those treatments that were isolated with an exclusion bag without being handpollinated. Sodium alginate isolation also increased the efficiency of control-pollinations as the gel was naturally shed, removing the need for operators to return to the tree to remove the isolation material.