Surrogate pollen induction shortens the breeding cycle in loblolly pine

Surrogate pollen induction (SPI) was evaluated on loblolly pine (Pinus taeda L.) donor scions from 5-year-old progeny that were grafted by topworking into the lower crowns of 16-year-old loblolly pine receptor clones in a seed orchard. On each of 25 study trees, one of three pollen induction treatments (wire girdle, saw girdle or control) was applied to 10 receptor branches below the graft location. Graft survival was 76%. Of the surviving grafts, 57% produced pollen strobili in March 1993, 13 months after grafting. The pollen induction treatments did not decrease graft survival or increase pollen production. Graft survival did not vary significantly among the donor scion genotypes, but the percentage of grafts with pollen was significantly related to the donor scion genotype. The mean number of pollen clusters induced per ramet also differed significantly among the donor scions. There was a tendency for pollen phenology of the grafted scions to be modified by the receptor clone. We conclude that surrogate pollen induction, coupled with accelerated female flower stimulation, can reduce the breeding schedule in loblolly pine to 3 years.