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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

  1. Robinson, R. W. 1978. Association of fruit shape and sex expression in the cucumber. Cucurbit Genetics Coop. Rpt. 1:10.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 23 October, 2009