Cucurbit Genetics Cooperative Report 4:8-10 (article 4) 1981
Effects of Ethylene on Hermaphroditic Cucumbers
Amy Iezzoni and C. E. Peterson
University of Wisconsin,
Madison, WI 53706
Ethrel, an ethylene releasing compound, has been demonstrated
to alter the growth and flowering habit of monoecious cucumbers.
Several of the most striking alterations include a decrease
in internode length and a reduction of staminate flowers
with an increased number of pistillate flowers produced
at earlier nodes along the man stem. Very little work has
been reported on the effects of Ethrel on bisexual lines.
Robinson (1) notes that Ethrel application to the andromonoecious
cultivar Lemon induced the development of pistillate flowers.
The resulting pistillate flowers had elongated fruit as
opposed to the round fruit from perfect flowers.
Fruit setting and seed production has traditionally been
difficult on bisexual lines. The ovaries of bisexual flowers
are short, thick, rounded, and capable of producing fruit
with only bout 25% as many seeds as those from pistillate
flowers. The first objective of this experiment was to determine
if Ethrel could be used to increase ovary length, fruit
length, and seed yield.
It is difficult to predict certain fruit characters of
the hybrid between a hermaphroditic and gynoecious line
because the short rough fruit of the perfect flowered lines
hide the genetic potential that these lines possess for
many size and quality characteristics. Usually it is necessary
to testcross with gynoecious lines to determine combining
ability of the hermaphroditic genotype. The second objective
of this experiment was to learn if Ethrel treatment of hermaphroditic
lines will reveal their genetic potential for several fruit
and quality characteristics.
The four hermaphroditic lines tested were 1913, 3010, 2091,
and 2113. Lines 2091 and 2113 were chosen because they produced
dissimilar phenotypes in crosses with a pickling-type gynoecious
line, 1606. The 1606 x 2091 hybrid had pickling-type fruits
with rough warty light green skin and a length:diameter
ratio (L/D) of about 3:1. The 1606 x 2113 hybrid had distinctly
longer fruit with smooth dark green skin.
An untreated control plus four Ethrel treatments were used:
150 ppm applied once (1x), 150 ppm applied twice (2x), 250
ppm (1x) and 250 ppm (2x). The first treatment was applied
at the third true leaf stage and when appropriate, a second
application was applied one week later. Each line-treatment
combination was replicated four times. Data was taken on
plant height 20 days after the first Ethrel application,
ovary length, presence or absence of anthers, fruit length,
fruit width, skin color and texture, and the number of seeds
per fruit. Pollinations were mae with line 1568 which was
producing an abundance of staminate flowers at the time.
Anthers did not develop in plants treated with Ethrel at
150 ppm (2x) and 250 ppm (2x), but occasionally occurred
in plants treated with 250 ppm (1x). All Ethrel treatments
reduced plant height by reducing internode length (Table
1). The 250 ppm (2x) treatment is not recommended because
of severe stunting. Ovary length was consistently increased
by all treatments of Ethrel for lines 2091, 3010, and 2113.
Line 1913 which had the longest ovary when untreated, did
not respond to any of the Ethrel treatments. About five
weeks after Ethrel application, ovary lengths decreased
to near normal and anther development resumed.
Fruit lengths were increased over the untreated control
for lines 2091, 3010, and 2113. The longest fruit which
developed on an Ethrel treated 2113 plant was 8.06 cm above
the untreated mean for that line; whereas, the longest fruit
from a treated 2091 line was 6.25 cm above its untreated
mean. Line 1913 which had the longest fruit when untreated,
failed to respond with longer fruits. No significant changes
in fruit width resulted and the overall fruit size response
was an increase in the L/D ratio.
With two out of the four hermaphroditic lines, Ethrel caused
a striking change in skin texture and color. Fruits from
3010 and 2113 normally had many spines and warts on a blotchy
yellow background. All Ethrel treatments reduced the number
of spines and warts on these fruits and caused a shift to
a dark green skin color. Ethrel treatment on lines 1913
and 2091 did not produce changes in color and texture and
all fruits developed warts and a yellowish skin.
Seed yield of all the lines was significantly increased
by the three highest Ethrel treatments [150 ppm (2x), 250
ppm (1x), 250 ppm (2x)]. In many cases, pollination was
facilitated because there were no anthers, and any injury
to the stigma which might have occurred during the emasculation
procedure was eliminated. Also, the long epigynous ovary
of the treated plants initiated more ovules along the lengthened
placental region increasing the potential for seed set.
Unfortunately, many of the fruit from the 250 ppm (1x) and
250 ppm (2x) plants were pear-shaped because of inadequate
pollination. A similar experiment is planned for the field
where bee activity should insure complete pollination.
The response of the two inbreds 2091 and 2113 to Ethrel
mimicked the phenotype of their hybrid with the pickling
type gynoecious inbred 1606. The hybrid 1606 x 2091 had
the characteristic short pickle shape with yellow-green
skin while 1606 x 2113 resembled a long slicer type with
smooth dark green skin. Line 2113 also had a greater increase
in fruit length with Ethrel treatment than did 2091.
Ethrel application to these four hermaphroditic lines resulted
in many simultaneous phenotypic changes suggesting that
anther development, fruit shape, and skin color and texture,
may be affected by the same endogenous hormone. It is possible
that the Ethrel treatments is supplying the hormone which
is somehow produced or controlled by the M gene.
The association of the M locus with the ethylene
hormone may help explain the seemingly pleiotropic effects
of sex expression and fruit shape. In the F1, the M
locus would be heterozygous and could provide the enzyme
contributing to anther suppression and ovary shape. By spraying
the hermaphroditic lines with Ethrel it may be possible
to supply the substance produced or controlled by the M
locus and reveal the genetic potential that a hermaphroditic
line might contribute to the hybrid phenotype.
Table 1. Effects of Ethrel on plant height, ovary length, fruit length, and number of seeds per fruit of 4 hermaphroditic cucumber lines.
|
Plant Height (cm) y |
Ovary Length (mm) x |
Fruit Length (cm) y |
No. of seeds per
fruit y |
Ethrel treatment z |
2113 |
1913 |
2091 |
3010 |
2113 |
1913 |
2091 |
3010 |
2113 |
1913 |
2091 |
3010 |
2113 |
1913 |
2091 |
3010 |
0 |
46.2 |
85.2 |
66.0 |
59.8 |
14.2 |
19.9 |
10.4 |
12.4 |
8.9 |
11.4 |
6.8 |
6.0 |
81.0 |
78.2 |
52.2 |
68.5 |
150 ppm (1x) |
36.0 |
67.5 |
52.8 |
32.8 |
25.1 |
21.2 |
12.9 |
17.0 |
12.8 |
11.4 |
9.3 |
8.5 |
71.0 |
75.8 |
60.2 |
82.2 |
150 ppm (2x) |
28.8 |
27.8 |
34.2 |
36.0 |
25.0 |
19.6 |
18.6 |
20.2 |
13.0 |
11.0 |
11.8 |
10.5 |
100.5 |
205.8 |
153.0 |
131.2 |
250 ppm (1x) |
34.8 |
50.0 |
43.2 |
38.2 |
30.8 |
19.9 |
15.4 |
21.6 |
15.5 |
12.1 |
10.8 |
10.0 |
92.0 |
150.8 |
165.0 |
113.5 |
250 ppm (2x) |
26.7 |
36.5 |
30.0 |
29.5 |
28.4 |
21.3 |
19.0 |
22.0 |
13.7 |
11.0 |
12.4 |
11.1 |
90.5 |
147.8 |
137.8 |
99.5 |
LSD (0.05) |
6.35 |
1.29 |
0.89 |
17.3 |
z Single treatments were made at the third true leaf stage. Additional treatments were made 7 days later.
y Mean of 4 reps per treatment.
x Mean of 3 ovary lengths per plants of 4 reps per treatment.
Literature Cited
- Robinson, R. W. 1978. Association of fruit shape and
sex expression in the cucumber. Cucurbit Genetics
Coop. Rpt. 1:10.
