Hybridization of E. deglupta and E. “decaisneana”

I was certain that these were natural genetic hybrids of Eucalyptus torelliana♀ x Eucalyptus citriodora♂53 that had occurred at the location of the seed collection for E. torelliana. When this observation was reported to HQ, a senior officer wrote back dismissing them as “sports”54 of no consequence. There was no further opportunity for observation or debate as most of the mixed eucalypt stand and the hybrids in Heads Hump LA were killed by fire in August 1972.

Hybridization of E. deglupta and E. “decaisneana”

The availability of pollen from a nearby provenance trial of E. “decaisneana” prompted me to try to produce a hybrid with E. deglupta as the female parent. Some flowers, which had already emerged near ground level on recent grafts of E. deglupta in the Geshes seed orchard, were emasculated, dusted with E. “decaisneana” pollen and bagged with unwoven terylene bags. This first attempt in 1972 was unsuccessful and I did not repeat the experiment, as I did not have sufficient knowledge then about how long the pollen of E. “decaisneana” remained viable.

Left: Source trees for donor pollen in the provenance trial of E. “decaisneana” at Bulolo. Right: I am bagging flowers on a very early flowering young graft of E. deglupta after emasculation and an attempt at artificial cross-pollination with E. “decaisneana” pollen, Geshes seed orchard area, Bulolo, 1972.

53 Later reclassified in the new eucalypt genus Corymbia as Corymbia torelliana and Corymbia citriodora respectively. 54 In botany a “sport” is a part of a plant that shows morphological (phenotypic as distinct from genotypic) differences from the rest of the plant. Sports may differ by foliage shape, colour of flowers, fruit or branch structure.