Crossability of Populus species

(OCDE 2000)

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Extensive crossability studies have been carried out among species in the Populus, Tacamahaca and Aigeiros sections, while few data are available for those in Turanga and Leucoides.

Hybrids between members of the same section are produced easily and are often more vigorous than their parents. Dramatic examples are the hybrids made between P. tremuloides and P. tremula. Crossing success between sections is variable. Crosses between Aigeiros and Tacamahaca are easy, while those between sections Populus and Aigeiros, and sections Populus and Tacamahaca are notoriously difficult, resulting normally in dead seed or dwarfed seedlings. Crosses between sections are sometimes made more easily using interspecific hybrids, rather than pure species, as parents.

The incompatibility of some species is characterised by arrested development of the pollen tube and failure to penetrate the stigma. This block can be overcome in some cases by mixing the incompatible pollen with "mentor pollen", i.e., compatible pollen that has been killed by means of gamma radiation, and by treatment of pollen and stigmas with solvents and extracts from compatible pollen. This technique has made it possible to obtain crosses of section Populus with Aigeiros and Tacamahaca poplars that are otherwise difficult.

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