Cucurbit Genetics Cooperative Report 3:52-54 (article 31) 1980
In Vivo Pollen Tube Growth as a Measure of Interspecific
Incongruity in Cucumis L.
Y.O. Kho, A.P.M. den Nijs and J. Franken
Institute
for Horticultural Plant Breeding, Wageningen, the Netherlands
Pollen tube growth in the style was studied in a diallel
involving ten African species of Cucumis as well
as C. sativus L. Several workers have studied interspecific
relationships within the genus by assessing fruit and seed
set and fertility of hybrid offspring. The present work
extends this knowledge to the location of the barriers to
pollen tube growth in the stigma, style and ovary. Moreover,
almost all species in this study were represented by several
accessions so that some insight was gained in intra-specific
variability with respect to crossability. All accessions
were identified taxonomically and are listed with their
author.
For each combination in each year at least three flowers
(and mostly a larger number) were pollinated. Pollen tube
behavior was examined by UV microscopy of flowers three
days after pollination.
Plants were grown in the summer in a glasshouse (25°C
D/18°C N). Almost all crosses were repeated in three
consecutive seasons. As there were no great discrepancies
among the results in the different years, we combined all
data. All species were monoecious except the cultivated
melons. Only monoecious feral melons (type agrestis)
were employed as female parent to avoid ambiguities due
to emasculation. In most species the different accessions
(Genebank numbers, Gbn) behaved similarly, so the results
were pooled per species. Notable exceptions are C. sativus
with five accessions and C. anguria with three.
Four accessions of C. sativus can be tentatively
designated as primitive or hardwickii-types. The
fifth is C. sativus var. sikkimensis.
The results of our investigation are in Table 1. For explanation
of the figures, see the legends of the table. Some of the
conclusions are as follows:
- Selfing pollinations and intraspecific crosses result in good penetration
of pollen tubes into numerous ovules of all species.
- Part of the African species appear congruous.
- Cucumis myriocarpus and C. ficifolius
appear unilaterally incongruous with most representatives
of the African group. Cucumis myriocarpus, when
used as a staminate parent, gives better results than
in reciprocal crosses whereas with C. ficifolius,
the reverse is true.
- Cucumis metuliferus is strictly separated from
most of its relatives.
- All accessions of C. sativus are, to some extent,
mutually congruous though not as fully as might be expected
of a single species. There is even evidence for unilateral
incongruity.
- Combinations between C. sativus and any of
the African species exhibited restricted pollen tube growth,
except several crosses of C. sativus x C.
melo. The reciprocals of these crosses do not allow
tube growth.
- Of all african species tested, C. melo appeared to be
most promising for use as a bridge between several species
with resistances and C. sativus.
More intensive investigations of the most useful combinations
are in progress. More detailed results (a.o. on identification,
variation between accessions, fruit and seed set, embryo
culture, nature and fertility of obtained hybrids) will
be published shortly.
Table 1. Pollen tube (p.t.) growth in the style in interspecific
crosses in Cucumis L.
|
|
Male Parent |
|
Female Parent |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
1 |
Cucumis africanus L.f., Gbn. 0162.0181.0330 |
4 |
3(4) |
3(4) |
3(4) |
3(4) |
2 |
2(3) |
3(4) |
4 |
1(2) |
1(2) |
1 |
2 |
1(2) |
1(2) |
2 |
2 |
C. anguria L., Gbn 0307.0310 |
3(4) |
4 |
4 |
4 |
2 |
|
2 |
4 |
4 |
2 |
3(4) |
1 |
2 |
2 |
2 |
2 |
3 |
C. anguria L., Gbn. 1758 |
2 |
4 |
4 |
|
|
1 |
1 |
2 |
4 |
1 |
1 |
1 |
1 |
2 |
|
|
4 |
C. myriocarpus Naud., Gbn. 0182.1776 |
2(3) |
2 |
1 |
4 |
1 |
1 |
1 |
2 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
5 |
C. zeyheri Sond., Gbn. 1053 |
4 |
3(4) |
2 |
3(4) |
4 |
3 |
3 |
3(4) |
4 |
1 |
2(3) |
1 |
1 |
1(2) |
|
1(2) |
6 |
C. figarei Naud., Gbn 1707 |
3 |
|
1 |
3(4) |
|
4 |
3 |
3 |
3 |
3 |
2 |
2 |
2(3) |
2 |
2(3) |
3 |
7 |
C. ficifolius A, Rich., Gbn. 1729 |
4 |
4 |
4 |
4 |
4 |
3(4) |
4 |
4 |
4 |
3 |
2(3) |
2 |
2 |
2 |
3 |
2 |
8 |
C. dipsaceus Spach., Gbn. 0163 |
4 |
3 |
|
4 |
4 |
3 |
3 |
4 |
4 |
3 |
2(3) |
1 |
2 |
1 |
3 |
1 |
9 |
C. prophetarum L., Gbn. 1751 |
3 |
4 |
4 |
3 |
1 |
1 |
1 |
1 |
4 |
1 |
1 |
1 |
1 |
1 |
0(1) |
0(1) |
10 |
C. metuliferus Naud., Gbn. 0164.1734.1747 |
2 |
1 |
2 |
2 |
3 |
1(2) |
1 |
2 |
2 |
4 |
2 |
2 |
2 |
2 |
2 |
2 |
11 |
C. melo L., Gbn. 0309.1777.1717 |
1 |
1 |
1 |
1 |
0(1) |
1 |
1 |
0(1) |
0(1) |
1 |
4 |
0 |
1 |
0(1) |
0(1) |
1 |
12 |
C. sativus L., Gbn. 1739 |
1 |
1 |
|
1 |
|
0 |
1 |
0(1) |
2 |
1 |
1 |
4 |
1 |
1 |
1 |
1 |
13 |
Gbn. 1811 |
3 |
1 |
1 |
1 |
1 |
0(1) |
1 |
|
1 |
1 |
3 |
3 |
4 |
4 |
|
4 |
14 |
Gbn. 0777 |
3 |
3 |
2 |
2 |
3 |
1 |
1 |
1 |
|
1 |
4 |
3 |
3 |
4 |
4 |
4 |
15 |
Gbn. 1753 |
2(3) |
0(1) |
|
1(2) |
3 |
1 |
1 |
1 |
3 |
1 |
3 |
3 |
|
4 |
4 |
3 |
16 |
Var. sikkimensis Hook. |
2 |
1 |
1 |
2(3) |
1(2) |
0(1) |
1 |
1 |
1 |
1 |
3 |
3 |
3 |
3 |
4 |
4 |
Legends: 0 = no p.t. in stigma; 1 = p.t. in stigma; p.t.
in style; 3 = p.t. in ovary; 4 = p.t. in ovule; ( ) a few
pollen tubes.
