Re: [Aroid-l] Intrageneric crossing - a good
H. Yoshino, T. Ochiai and M. Tahara (2000) Phylogenetic
relationship between Colocasia and Alocasia based on
molecular techniques. In: D. Zhu, P. B. Ezyaguirre, M. Zhou, L. Sears
and G. Liu (eds) Ethnobotany and genetic diversity of Asian taro:
focus on China. International Plant Genetic Resources Institute
and Chinese Society for Horticultural Science, Beijing. pp.
A taro strain collected in Nepal in 1973 was considered to be an
intergeneric hybrid between Alocasia and Colocasia, on
the basis of chloroplast DNA analyses carried out in the 1980s (but
see later work with isozymes, noted below).
Subsequently, an artificial cross was attempted and numerous
seeds were obtained after a cross between C. esculenta var.
aquatilis (Hassk.) Kitamura (from Nepal) and Alocasia brisbanensis
(F. M. Bailey) Domin (ex Kyoto Botanical Garden). Most seeds did not
germinate and only a single plant developed fully.
This plant was triploid and chromosome painting using genomic
in situ hybridisation (GISH) showed that 14 of 42 chromosomes were
derived from A. brisbanensis.
It was concluded that the plant was an intergeneric hybrid,
formed as an unreduced egg of C. esculenta fertilised with
normal A. brisbanensis pollen.
Isozyme analyses by V. X. Nguyen (1998), PhD, Okayama
contradicted the original interpretation of the Nepalese hybrid,
indicating that it was a cross between C. esculenta and C.
gigantea (i.e. intra-generic, not inter-generic).
Comments by PJM:
Among other Asian accessions (Nepal and China) Nguyen found
further examples of hybridsation between C. esculenta and C.
gigantea. Taxonomically, C. gigantea is possibly misplaced
in Colocasia, but it is not necessarily to be regarded as
closer to Alocasia. As Yoshino points out, and as Tony Avent
indicates in this list, there is much to be learned about
hyribidisation among these aroids.
The experimental survival of a hybrid between genera was made
possible by a rare polyploidisation event that allowed odd chromosomes
to be carried along by a normal full complement of chromosomes.
Vigorous offspring are less likely after intergeneric crosses
than after interspecies (intrageneric) crosses. An intergeneric
crossing has not yet been proven to occur in the wild, though it is
possible in principle.
Dear Pete and Marek:
The Alocasia x Colocasia hybrid that you mentioned looks a lot like A.
macrorhizos. I was fortunate to examine this hybrid several
years ago growing at a Hawaii taro research station. It was
found in an area of Nepal where the two genera grow together.
On our expedition last year to N. Vietnam, we visited a restricted
military area near the China border. We found Colocasia gigantea
growing with Alocasia macrorhizos. Growing among them were
several plants that superficially appeared to be bi-generic hybrids.
We have not had these plants tested yet to confirm this yet, so this
is just a preliminary observation. If anyone is doing work in
that region, I will be glad to direct them to the population for
Plant Delights Nursery @
Juniper Level Botanic Garden
9241 Sauls Road
Raleigh, North Carolina 27603 USA
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phone 919 772-4794
fax 919 772-4752
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