Agriculture Reference
In-Depth Information
raised to the species level on the Solanaceae
Source website). Refraining from using infra-
specific classification certainly lessens the no-
menclatural burden that is already excessive due
to the extensive synonymy created.
and Uruguay, devoted much attention to the oc-
currence of natural hybrids and also performed
many crossing experiments to check the parent-
age of presumed hybrids. They made the point
that the presence of these natural hybrids led to
difficulties in classification and identification,
and stressed the necessity of studying living ma-
terial. They made the following observation:
Series classification
Not all of the many series recognized within sec-
tion
Petota
are natural units and the system is
far from stable, with Correll (1962) recognizing
26
series versus Hawkes (1990) with
21
series.
Spooner and collaborators produced cpDNA phy-
logenies, using material of
17
of the
21
series rec-
ognized by Hawkes in section
Petota
, which
showed four main clades (Spooner and Castillo,
1997). Recent AFLP studies (Jacobs
et al
., 2008)
could not find support for most of the series, nor
for the four clades of Spooner and Castillo (1997).
Some of the series seem to be good, however, espe-
cially the diploid and tetraploid Mexican groups
that are apparent in many phylogenetic studies.
Spooner
et al
. (2004), studying the Central
American representatives of section
Petota
, de-
cided to recognize
11
informal “species groups”
rather than the formal taxon “series”. Most of the
South American series are probably artificial.
This was also shown by Jacobs
et al
. (2008), who
found a lack of phylogenetic structure, especially
in the part of the trees that contained the South
American species.
Perhaps at first sight it will be thought that we
have seen hybrids and introgressed forms
everywhere! We can assure the reader that we
have tried to resist this temptation as far as
possible, and have attempted not to fall into the
common trap of labelling everything as a hybrid
that does not fit into a preconceived narrow
concept of what each species should conform to.
(Hawkes and Hjerting, 1969, pp.
119-
120)
However, Spooner and Van den Berg (1992a)
noted that the main problem in the taxonomy
of section
Petota
was the lack of documentation
of morphological variability within taxa and
that most authors (e.g. Correll, 1962; Hawkes,
1990; Ochoa, 1990) indicated the necessity to
use a broad species concept, but that, in practice,
many taxa were narrowly defined by minor and
often overlapping character states and variabil-
ity frequently either was not documented or
was ignored.
Spooner and Van den Berg (1992b) exam-
ined the status of the species
Solanum berthaultii
and
Solanum tarijense
. These were treated as dis-
tinct, and even as belonging to different superser-
ies, by Hawkes (1990), and the many intermediate
forms were ascribed to extensive hybridization.
The morphological data of Spooner and Van den
Berg (1992b) suggested the possibility that the
two species were the extremes of a continuous
range of variability and that they should be
treated as one species, and Spooner
et al
. (2007a)
confirmed this with AFLP and chloroplast re-
striction site data.
Hybrids
Crosses between species that share the same
EBN are, in principle, possible (even between dif-
ferent ploidy levels), and hybridization is a com-
mon phenomenon. The majority of the diploid
representatives of section
Petota
are outcrossing
species that are able to cross with each other, oc-
casionally resulting in the establishment of a hy-
brid population that maintains itself. A number
of these have been recognized as “nothospecies”
and have been given Linnean names. In other
cases, populations have been indicated with a
hybrid formula indicating their parental species.
Backcrosses and crosses between different gen-
erations may produce complicated hybrid
swarms, while backcrosses to one of the paren-
tal species may cause introgression.
Hawkes and Hjerting (1969), in their treat-
ment of the potatoes of Argentina, Brazil, Paraguay,
Present situation
We here compare two recent initiatives to arrive
at an updated taxonomy of the potato and its wild
relatives, viz. the CBSG project (Centre of Biosys-
tem Genomics) and the Solanaceae Source website.
The CBSG project, conducted from 2003 onwards,
aimed to provide a phylogenetic backbone of
Solanum
