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Cucurbit Genetics Cooperative Report 20:7-8 (article 4) 1997

Measurement of Sex Expression in Cucumber Using Percentage Staminate Nodes and a Subjective Rating for Gynoecy

Nischit V. Shetty and Todd C. Wehner

Department of Horticultural Science, North Carolina State University, Raleigh NC 27695-7609

Most cultivars of cucumber (Cucumis sativus L.) grown in the U.S. are gynoecious hybrids. In order to produce hybrid seeds of those cultivars, one inbred parent must be highly gynoecious. Therefore, cucumber breeders are interested in a fast, accurate, and easy method for evaluating sex expression of plants in the field.

In North Carolina trials, we measure the sex expression of cucumber by counting the number of nodes with at least one staminate flower in the first five nodes above the cotyledon. Recently, we have been using a subjective rating system in order to provide a faster method that gives a better idea of the sex expression of plant. The rating scale is from 1 to 9, with 1=androecious, and 9=gynoecious.

The objective of this study was to evaluate the subjective rating system for sex expression with regard to error variation, and correlation with percentage staminate nodes.

Methods. The experiment was conducted during the summer season, 1995, at the Horticultural Crops Research Station at Clinton, NC. Recommended horticultural practices were used. Plants were grown on a trellis or a flat bed system. Eighteen cultivars were evaluated: 15 oriental trellis cucumbers and 3 American slicers. Each cultivar was planted in plots 6.0m long. Plots were on raised, shaped beds with centers 1.5m apart. Fertilizer was applied at the recommended rates of 90-39-74 kg haˉ¹ (N-P-K), with an additional 34 kg haˉ¹ N applied at the vine tip-over stage. Irrigation was applied at the rate of 25 to 40 mm per week. A tank mix of 2.2 kg haˉ¹ of naptalam and 4.4 kg haˉ¹ of bensulide (O, O-bis(1-methylethyl) S-[2-[(phenylsulfonyl) amino] ethyl] phosphorodithioate) was applied preplant for weed control.

Wooden posts 0.15 x 0.15 x 2.1 m were used as support for the trellis system. The posts were erected in holes 0.6 m deep, with a 3 m spacing between posts. The experiment had 6 rows of trellises, each 60m long. Two steel wires of 2 mm diameter were supported by the posts in each row at a height of 0.45 m and 1.5 m from the ground level. The wires were held tightly to a steel brace at either end of the row. Cotton twine was passed between the two steel wires. The plants were trained onto the twine.

The experiment was a randomized complete block design with 2 systems (trellis and flat bed), 18 cultivars, 3 replications, and 40 plants per plot, with a total of 108 field plots. Data were analyzed using the GLM and correlation procedures of SAS (SAS Institute, Inc., Cary, NC). Field plots for the cucumber cultivars on trellis and flat bed systems were rated for sex expression 7 weeks after planting. The percentage staminate nodes was counted on the first 5 nodes of 5 plants per plot. Gynoecious plants would have few or no male nodes. The gynoecious rating used a 1 to 9 scale (1-3=androecious, 4-6=monoecious, 7-9=gynoecious).

Results. No significant differences between the two production systems were observed for percentage staminate nodes or gynoecious rating. The correlation between the percentage of staminate nodes and gynoecious rating for trellis and flat beds were -0.27 and -0.39, respectively. The regression equation fitting percentage staminate nodes as the dependent variable for the cultivars on trellis and flat bed system were GR=5.4157-0.0118x%SN and GR=6.7033-0.023x%SN.

The range/LSD for percentage staminate nodes on trellis and flat beds was 2.79 and 3.18, respectively, with CVs of 35 and 30 (Table 1). The range?LSD for gynoecious rating on trellis and flat beds was 4 and 2, respectively, with CVs of 19 and 24. The range/LSD for percentage staminate nodes, and for gynoecious rating indicated that the cultivars could be divided into 2 to 4 groups for sex expression: gynoecious, predominately gynoecious, and monoecious.

The most gynoecious cultivars based on percentage of staminate nodes on both trellis and flat beds were 'Sprint 440' and 'Sky Horse' (Table 1). The most androecious cultivars on trellis support were 'XZ #17', 'Jin Za #2', and 'Tasty Green'. Based on gynoecious rating, the most gynoecious cultivars on trellis support were 'Sprint 440', 'Jin Chun #4', and 'XZ #17' and monoecious cultivars were 'Marketmore 76', 'Poinsett 76' and 'Tasty Bright'.

On flat beds the most androecious cultivars based on percentage of staminate nodes were 'Tasty Green', 'Jin Chun #4', and 'Yangzhou String'. Based on gynoecious ratings, the most gynoecious cultivars on trellis support were 'Jin Za #2', '89-211', and 'Sky Horse', and the monoecious cultivars were 'Marketmore 76', 'Tasty Bright', and 'Hongzhou Green 55' (table 1).

Although the two methods for measuring sex expression provided similar data, and were correlated, the correlation was not high. Therefore, it appears that the two methods were different things. Percentage staminate nodes was easier to standardize among workers since it is an objective method. However, we found the gynoecious rating to be faster and easier, and were able to use different workers by assigning each to a different replication. Finally, gynoecious rating gives sex expression for all nodes on the plants rather than just the first five, so is more useful for plant breeders working to develop stable, highly gynoecious inbreds.

Table 1. Compassion of sex expression in 18 cucumber cultivars grown on trellis and flat bed production systems using two different measurement methods.

Cultivar Source
Percentage staminate nodes
Gynoecious rating (1-9)
Percentage staminate nodes
Gynoecious rating (1-9)
Sprint 440 Asgrow Seed
10
7
19
6
Jin Chun #4 Tianjin, PRC
65
6
89
4
Fengyan Taiwan
45
5
77
6
Sky Horse Japan
48
5
20
7
I 109 Japan
59
5
57
5
BAU #14 Beijing Agric. Univ.
61
5
69
5
Yangzhou String Yangzhou, PRC
65
5
85
4
89-211 Japan
68
5
65
7
Jin Za #2 Tianjin, PRC
75
5
70
7
XZ #17 Shanghai, PRC
77
5
65
4
Tasty Bright Sakata Seed
55
4
45
4
Summer Top Takii Seed
62
4
41
6
Yangzhou Grn. Skn. Yangzhou, PRC
65
4
61
6
Jin Yan #4 Tianjin, PRC
65
4
71
4
Hongzhou Green 55 Hongzhou, PRC
71
4
63
4
Tasty Green Sakata Seed
71
4
89
4
Marketmore 76 Cornell Univ.
51
3
59
3
Poinsett 76 Cornell Univ.
61
3
63
5
Mean  

60

5
62
5
LSD (5%)  
24
1
22
2
CV  
35
19
30
24
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Department of Horticultural Science Box 7609North Carolina State UniversityRaleigh, NC 27695-7609919-515-5363
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 15 December, 2009