Artificially induced protogyny: an advance in the controlled pollination of Eucalyptus

Summary

Artificially induced protogyny (AIP) is a new technique for the controlled pollination of Eucalyptus, without emasculation. AIP involves cutting off the tip of the operculum of the mature flower bud just prior to anthesis, with the cut positioned so as to remove the stigma, and then applying the target pollen to the exposed cut-surface of the upper style.

In trials in Brazil and Australia, rates of capsule retention and seed yield, and therefore yields of seeds per bud pollinated, have been very similar for AIP and one-stop pollination (OSP). However, AIP has achieved a 3–18-fold increase in productivity over OSP and conventional (three-visit) methods, in terms of seed produced per operator hour.

Contamination levels in the Brazilian experiment ranged from 3.75% in buds pollinated at the ripe/yellow stage, to 0.77% in buds pollinated at the immature/green stage. The yield of 2.0 seeds per bud pollinated with AIP at the immature/green stage was unacceptably low compared with 17.2 seeds per bud at the ripe/yellow stage. Molecular genetic analysis of seedlings produced from one of the E. grandis x E. camaldulensis crosses in Australia confirmed that all 20 seedlings were from the target cross.

The high operator productivity and relatively low levels of contamination achieved with AIP, across several eucalypt species, make it a potentially attractive technique for operational crossing. Our experiments were carried out in indoor clone banks that contained very few potential insect pollinators, so self-pollination is likely to be the main source of the contamination observed in the Brazilian experiments. Higher levels of contamination from non-target outcross pollen may occur following AIP on trees exposed to normal levels of pollinator activity.

Keywords:

• plant breeding methods
• cross pollination
• seed production
• techniques
• Eucalyptus