Cucurbit Genetics Cooperative Report 7:27-30 (article
13) 1984
Electrophoretic Comparison of Six Species of Cucumis
J.E. Staub and R.S. Kupper
Department of Horticulture, University of Wisconsin, Madison, WI
53706
T.C. Wehner
Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609
Evolutionary studies in the genus Cucumis have been
conducted by Dane (2) and Esquinas-Alcazar (3) using isozymes as
biochemical markers. In the study of Esquinas-Alcazar,
electrophoretic variability was examined in 155 populations
representing 21 species of Cucumis to determine
intraspecific relationships within the species C. melo L.
and interspecific relationships within the genus Cucumis.
He used 6 enzymes [peroxidase (PRX), acid phosphatase (APR),
glutamate oxalacetase transaminase (GOT),
glucosephosphateisomerase (GPI), phosphoglucomutase (PGM), and 6-
phosphoglucodehydrogenase (6-PDGH)] which were coded for a total
of 16 enzyme-coding loci. The 21 species of Cucumis were
classified, on the basis of genetic distances, into 4 groups.
The anguria group included: C. africanus, C.
anguria, C. ficifolius, C. myriocarpus, and C. zeyheri, while the sativus group included: C.
sativus, C. hardwickii, and C. trigonus.
Two highly speculative hypotheses were proposed for the evolution
of the sativus group. The hypotheses consisted of the
following:
- The group could have been derived from an ancestral form of the metuliferus group through a primitive C. hardwickii following a reduction of chromosome number. This hypothesis is
supported by the fact that the metuliferus group, which
includes C. membranifolium, C. metuliferus and C. sagittatus is genetically close to the anguria and sativus groups. Moreover, Trivedi and Roy (8)
concluded from cytogenetic studies that 12 might be the prime
base chromosome number of Cucumis.
- The ancestral form of the metuliferus group and the sativus group could have had a common ancestor with 2n=14
chromosomes. This hypothesis implies that Cucumis species
with a basic chromosome number x=12 evolved from those with 7
(1,4). Given that an unusual number of gene duplications have
been observed between these groups (3), such duplication of
genetic material could have taken place during the change in
chromosome number.
In an earlier report (7), we documented the relative activity of
47 general metabolic enzymes and general protein in different
tissues of selected botanical varieties of Cucumis [Cucumis sativus var. sativus L. and var. hardwickii (Royle) Kitamura]. In addition, we determined
that enzyme polymorphisms existed in GPI, GR, isocitrate
dehydrogenase (IDH), peptidase with phenyl-alanyl-proline (PEP-
PAP), phosphogluconate dehydrogenase (PGD) and phosphoglucomutase
(PGM). In this report we compare the electrophoretic phenotypes
of several species of Cucumis for 16 enzymes [those
mentioned above plus acid phosphatase (ACP), alkaline phosphatase
(AKP), diaphorase (DIA), esterase (EST), fructose diphosphatase
(FDP), glutamic pyruvic transaminase (GPT), leucine
aminopeptidase (LAP), malate dehydrogenase (MDH), shikimic
dehydrogenase (SKDH), and triose phosphate isomerase (TPI)]
coding for 19 loci. The objective of this study was to compare
zymograms of each of the loci to determine the magnitude of
potential genetic difference between several species of the anguria and sativus groups as classified by
Esquinas-Alcazar.
Cotyledonary extracts of 5 Cucumis species of African
origin, 3 Cucumis sativus var. hardwickii and 6
var. sativus were examined by horizontal starch gel
electrophoresis. Isozyme banding patterns of the enzymes were
recorded and comparisons were made among zymograms (Table 1).
Table 1. Electrophoretic variation in 19 enzyme loci of several
species in the genus Cucumis. |
Species or botanical variety |
Cultivar name, inbred identification or PI no.z |
Sourcey |
Chromosome no. |
Electrophoretic Phenotypes of Enzyme
Locix |
Acp |
Akp |
Dia-1 |
Dia-2 |
Est |
Fdp |
Gpi |
Gpt |
Gr-1 |
Gr-2 |
Idh |
Lap |
Mdh |
Pep-pap |
Pgd-1 |
Pgd-2 |
Pgm |
Skdh |
Tpi |
C. africanus |
299570 |
S. Africa |
24 |
4 |
11 |
2 |
22 |
24 |
11 |
33 |
11 |
-- |
12 |
22 |
2 |
2 |
11 |
22 |
33 |
34 |
12 |
3 |
C. anguria |
147065 |
Brazil |
24 |
3 |
11 |
3 |
-- |
33 |
11 |
33 |
11 |
-- |
12 |
22 |
3 |
3 |
22 |
22 |
33 |
33 |
22 |
2 |
C. ficifolius |
196844 |
Ethiopia |
48 |
2 |
11 |
2 |
-- |
-- |
-- |
23 |
11 |
-- |
12 |
22 |
3 |
4 |
-- |
22 |
33 |
33 |
22 |
1 |
C. myriocarpus |
282447 |
S. Africa |
24 |
3 |
12 |
3 |
22 |
33 |
11 |
33 |
22 |
11 |
12 |
22 |
4 |
3 |
22 |
22 |
33 |
33 |
23 |
2 |
C. zeyheri |
282450 |
S. Africa |
24 |
3 |
12 |
3 |
22 |
33 |
11 |
33 |
22 |
-- |
12 |
22 |
4 |
3 |
22 |
22 |
33 |
33 |
23 |
2 |
C. sativus var. hardwickii |
183967 |
Umran, Kashia Hills, India |
14 |
1 |
11 |
1 |
11 |
11 |
22 |
22 |
33 |
11 |
11 |
11 |
1 |
1 |
22 |
11 |
11 |
11 |
22 |
1 |
215589
| Dehra Dun, India |
14 |
1 |
11 |
1 |
11 |
11 |
22 |
22 |
33 |
22 |
11 |
11 |
1 |
1 |
22 |
11 |
11 |
11 |
22 |
1 |
462369 |
India |
14 |
1 |
11 |
1 |
11 |
11 |
22 |
22 |
33 |
11 |
11 |
33 |
1 |
1 |
11 |
11 |
11 |
11 |
22 |
1 |
C. sativus var. sativus |
Marbel |
Royal Sluis |
14 |
1 |
11 |
1 |
11 |
11 |
22 |
22 |
33 |
11 |
11 |
33 |
1 |
1 |
11 |
11 |
11 |
11 |
22 |
1 |
Riesenschall |
Royal Sluis |
14 |
1 |
11 |
1 |
11 |
11 |
22 |
22 |
33 |
11 |
12 |
33 |
1 |
1 |
11 |
11 |
22 |
22 |
22 |
1 |
GY 2* |
NCSU |
14 |
1 |
11 |
1 |
11 |
11 |
22 |
22 |
33 |
11 |
11 |
33 |
1 |
1 |
11 |
11 |
11 |
22 |
22 |
1 |
1397* |
USDA/ARS |
14 |
1 |
11 |
1 |
11 |
11 |
22 |
22 |
33 |
11 |
11 |
33 |
1 |
1 |
11 |
11 |
22 |
22 |
22 |
1 |
200815 |
Burma |
14 |
1 |
11 |
1 |
11 |
11 |
22 |
11 |
33 |
12 |
11 |
33 |
1 |
1 |
12 |
11 |
11 |
11 |
22 |
1 |
188807 |
Philippines |
14 |
1 |
11 |
1 |
11 |
11 |
22 |
22 |
33 |
12 |
12 |
33 |
1 |
1 |
11 |
11 |
22 |
11 |
22 |
1 |
| zInbreds are identified by "*". |
| yNCSU--North Carolina State University;
USDA/ARS-- United States Department of Agriculture/Agricultural Research
Service. |
| xDiagramatic representation of phenotypes
which have been given a single digit type number are provided in Figure
1. |
The allelic nomenclature follows a modified form described by
Richmond (5) such that loci coding for ACP, AKP, DIA, EST, FDP,
GPI, GPT, GR, IDH, LAP, MDH, PEP-PAP, PGD, PGM, SKDH, and TPI are
designated as Acp, Akp, Dia, Est, Fdp, Gpi, Gpt, Gr, Idh, Lap,
Mdh, Pep-pap, Pgd, Pgm, Skdh, and Tpi, respectively. Hyphenated
numerals refer to multiple loci, numbered from most cathodal to
most anodal. Alleles at a particular locus are designated by
numerals numbered from most cathodal to most anodal. As an
example, the combination of homomeric protein products of the
locus GR-1, which has at least 2 alleles (1 and 2), produce a
heteromeric product in a heterozygous individual which is
designated GR-1 (12). Where no immediate genetic interpretation
of the zymograms could be made, individual zymogram patterns were
given type numbers (Fig. 1).
 |
| Figure 1. A diagramatic representation of
electrophoretic variants observed in acid phosphatase,
diaphorase, leucine aminopeptidase, malate dehydrogenase, and
triose phosphate isomerase. Type numbers are given to identify
each zymogram. The position of an isozyme does not reflect its
relative mobility with regard to isozymes of other enzymes.
Therefore, comparisons of relative isozyme mobilities should be
made within and not between enzymes. |
Electrophoretic phenotypes of all collections grouped as sativus were monomorphic for Acp, Dia, Est, Fdp, Gpt, Lap,
Mdh, Pgd-1, Skah and Tpi, in which zymograms were single banded
(Table 1). Phenotypic variation among botanical varieties was
observed in Gpi, Gr-1, Gr-2, Idh, Pep-pap, Pgd-2 and Pgm. Those
species grouped as anguria were monomorphic for Fdp, Gr-2,
Idh, Pgd-1 and Pgd-2. If comparisons are made between groups,
unique patterns (types) or alleles exist for Acp, Dia-1, Dia-2,
Est,.Fdp, Gpi, Gpt, Idh, Lap, Mdh, Pgd-1, Pgd-2, Pqm and Tpi in
the anguria group which do not appear in the sativus group.
These data indicate that, although species within the groups
share some common alleles, enough difference exists between them
to suggest that their genetic distance is certainly as great as
Esquinas-Alcazar states. Moreover, comparisons among collections
in the sativus group suggest that the genetic relationship
between the two botanical varieties is probably much closer than
gross morphological differences (6) would lead one to believe.
These findings support the hypothesis of Dane (2) and Esquinas-
Alcazar (3) regarding the conspecific nature of var. sativus and var. hardwickii. It would be
interesting, with regard to the evolution of the genus Cucumis, to examine C. metuliferus and C.
longipes in more detail in order to determine their potential
relationship to C. sativus var. hardwickii and C. anguria.
Literature Cited
- Bhaduri, P.N. and P.C. Bose. 1947. Cytogenetical investigations
in some common cucurbits with specific reference to fragmentation
of chromosomes as a physical basis of speciation. J. Genet.
48:237-256.
- Dane, F.K. 1976. Evolutionary studies in the genus Cucumis.
Ph.D. Thesis, Colorado State University, Fort Collins, Colorado.
- Esquinas-Alcazar, J.T. 1977. Alloenzyme variation and
relationships in the genus Cucumis. Ph.D. Thesis,
University of California, Davis, California.
- Kozuchov, Z.A. 1930. Karyological investigations of the genus
Cucumis. (In Russian). Bul. Appl. Bot. Gen. and Plant Breeding
23:357-365.
- Richmond, R.C. 1972. Enzyme variability in the Drosophila williston
group. 3. Amounts of variability in the superspecies D. paulistorum.
Genetics 70:87-112.
- Schuman, D.A., J.E. Staub and B.E. Struckmeyer. 1982.
Morphological comparisons between Cucumis sativus and Cucumis hardwickii plants.
HortScience 17:108.
- Staub, J.E., R.S. Kupper and T.C. Wehner. 1983. Preliminary
evaluation of isozyme polymorphisms in Cucumis. Cucurbit
Gen. Coop. Rept. 6:32-34.
- Trivedi, R.N. and R.P. Roy. 1970. Cytological studies in Cucumis and Citrullus.
Cytologia 36:561-569.
|
|
