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Cucurbit Genetics Cooperative Report 8:67-68 (Article 25) 1985

Differential Sensitivity of Cucurbita pepo Cultivars to Ethephon

Edelstein, Menahem, Harry S. Paris, Haim Nerson, Zvi Karchi, and Yosef Burger

Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Experiment Station, P. O. Haifa, Israel

Initial reports of the effects of ethephon on both squash and cucumber were concerned with the ease with which relatively low concentrations were effective in converting the normally monoecious plants to femaleness for a given length of time. Later, George (1) reported that different genetic backgrounds of cucumbers exhibited differing degrees of conversion to temporary femaleness by ethephon, from easily converted to partially converted to virtually unaffected. Shannon and Robinson (4) reported that higher concentrations and more than one application were needed to convert summer squash (Cucurbita pepo L.) plants to femaleness under field conditions. They attributed this largely to the higher temperatures and longer days of summer field conditions, environmental factors which had previously been reported to favor maleness in C. pepo (2).

In the present investigation 2 C. pepo cultivars were compared for ease of conversion to femaleness under winter greenhouse conditions in Israel. One of these, 'Table Queen', was reported by Robinson et al. (3) to be easily converted to temporary femaleness by 250 ppm ethephon. The responsiveness of the other, 'Vegetable Spaghetti', to ethephon has not been previously described.

Seeds of 'Table Queen' were provided by Joseph Harris Co. and those of 'Vegetable Spaghetti' were acquired from Sakata Co. They were sown in the greenhouse on 14 January 1984 in 5-liter plastic pots that were filled with a mix of 1 soil: 1 peat: 1 vermiculite. For each of the cultivars there were 5 plants per treatment and 4 treatments: (a) control; or spraying to run-off with (b) 250 ppm ethephon at the 2-leaf stage, (c) 500 ppm at the 2-leaf stage, or (d) 500 ppm at the 2-leaf stage and again at the 4-leaf stage. Side branches and young fruits were removed during the course of the experiment. Flower sex and day of opening was recorded until the 30th node of each plant.

'Table Queen' produced more female flowers and had a higher ratio of female to male flowers than 'Vegetable Spaghetti' (Table 1). 'Table Queen' was also more easily converted to temporary femaleness. A concentration of 250 ppm was sufficient to suppress male flowering in terms of node of first male flower to reach anthesis, days from emergence to anthesis of first male flower, and number of male flowers to reach anthesis. This same concentration had no . significant effect on male flowering of 'Vegetable Spaghetti'. A concentration of 500 ppm suppressed male flowering in 'Table Queen' to such an extent that there was a 16-day span of anthesis of the first female to the first male flower. This concentration did not significantly lower the number of nodes to the first female flower, increase the number of female flowers, or hasten anthesis of female flowers. At 500 ppm, the changes that occurred in 'Vegetable Spaghetti' paralleled those that occurred in 'Table Queen' at 250 ppm, that is, there was some suppression of male flowers. With 2 applications of 500 ppm to 'Vegetable Spaghetti', the changes that occurred paralleled those in 'Table Queen' at 1 application of 500 ppm, that is, there was strong suppression of male flowers.

In this experiment sex conversion by ethephon was accomplished by suppressing male flowering but not by promoting female flowering. Of the 2 cultivars tested, the cultivar that was more strongly male was less easily converted to femaleness with ethephon than was the more strongly female cultivar. This situation is consistent with that reported for cucumbers (1) and that reported for 3 private inbreds of C. pepo (4). For hybrid seed production, each prospective female parent needs to be tested before commercial planting for its relative responsiveness to ethephon. 'Table Queen' and 'Vegetable Spaghetti' are potentially useful as checks for easy-to-convert and difficult-to-convert genotypes, respectively.

Table 1. Effects of ethephon on flowering and sex expression of 2 squash cultivars under winter greenhouse conditions.

 

Ethephon
concn.

Nodes to
first open
flower


Days from
emergence to
1st open flower


Number
of open
flowers


Ratio
Female
to Male

Cultivar

(ppm)

Male

Female

Male

Female

Male

Female

flowers


 

0

1.6 a

10.6 ab

35.4 a

31.4 a

20.0 d

12.2 c

1:1.6

Table

250

6.6 b

9.8 ab

39.4 b

31.0 a

15.2 c

9.0 b

1:1.7

Queen

500

18.6 c

8.4 a

48.8 d

32.2 a

8.6 b

9.4 bc

1:0.9

 

2 x 500

18.7 c

13.6 c

45.7 cd

36.0 bc

1.0 a

11.8 c

1:0.1

 

 

 

 

 

 

 

 

 

 

0

1.2 a

12.0 bc

36.4 ab

34.4 abc

19.6 d

8.B b

1:2.2

Vegetable

250

1.4 a

14.6 c

37.2 ab

37.4 c

21.8 d

6.0 a

1:3.6

Spaghetti

500

7.0 b

9.8 ab

41.4 bc

32.8 ab

16.6 c

7.0 ab

1:2.4

 

2 x 500

21.6 d

13.0 bc

53.6 e

36.0 bc

7.2 b

9.0 b

1:0.8


Mean separations within columns by Duncan's Multiple Range Test, 5% level.

Literature Cited

  1. George, W.L. Jr. 1971. Influence of genetic background on sex conversion
    by 2-chloroethylphosphonic acid in monoecious cucumbers. J. Amer. Soc.
    Hort. Sci. 96: 152-154.
  2. Nitsch, J.P., E.B. Kurtz Jr., J.L. Liverman, and F.W. Went. 1952. The
    development of sex expression in cucurbit flowers. Amer. J. Bot. 39:
    32-43.
  3. Robinson, R.W., T.W. Whitaker, and G.W. Bohn. 1970. Promotion of
    pistillate flowering in Cucurbita by 2-chloroethylphosphonic acid.
    Euphytica 19: 180-183.
  4. Shannon, S. and R.W. Robinson. 1979. The use of ethephon to regulate sex
    expression of summer squash for hybrid seed production. J. Amer. Soc.
    Hort. Sci. 104: 674-677.

Contribution No. 1340-E, 1985 series, from the Agricultural Research Organization, Bet Dagan, Israel.

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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
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