----- Original Message -----|
To: Discussion of aroids
Sent: Tuesday, January 24, 2006 1:16
Subject: Re: [Aroid-l] Intrageneric
crossing - a good reference
Peter:Your note is quite interesting about the possible
mis-classification of Colocasia gigantea. I have always found it unusual
that C. gigantea seems to have more phenotypic characteristics of alocasia
than colocasia...very interesting. Sounds like a research paper is
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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. 66-73.
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.
Isozyme analyses by V. X. Nguyen (1998), PhD, Okayama University,
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
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 further study.Tony
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