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Cucurbit Genetics Cooperative Report 2:14-15 (article 9) 1979

Silver Compounds Inducing Male Flowers in Gynoecious Cucumbers

A. P. M. den Nijs and D. L. Visser

Institute for Horticultural Plant Breeding, Wageningen, The Netherlands

Silver nitrate is now used widely in the greenhouse in The Netherlands. Occasionally, however, the treatment with AgNO3 results in severe burning and even loss of plants, especially when conditions are poor for growth. Delay of spraying until the second to third leaf stage and previous watering of the plants have been advised, but this has not always eliminated the problems.

While attempting to increase the longevity of cut carnations, Veen and Van de Geijn (1) demonstrated the manifold mobility of the silver ion in the anionic complex silver thiosulphate, [Ag(S203)2]3-, over that in AgNO3. The anti-ethylene action of this compound prompted us to assay its potential in sex reversion of gynoecious cucumbers. Initial trials indicated that Ag(S203)2 induced male flowers much the same as AgNO3. A more detailed experiment was carried out late in the fall of 1978.

Two gynoecious pickling cucumber lines (Al and A2), one slicing cucumber inbred (G6) and one commercial variety with known strong female background ('Farbio'), were planted in the greenhouse. There were nine treatments plus a water control: two concentrations of AgNO3, five of Ag(S203)2, one GA-3, and one GA-4/7 (Table 1). Plot size was four plants and there were two repetitions. Silver thiosulphate was prepared by adding excess Na(S203)2 to AgNO3 in the desired concentration, thereby shifting the equilibrium to Ag(S203)2. This is an anionic complex. Growth conditions favored spontaneous production of male flowers, but all of the plants in the control group remained gynoecious.

All treatments resulted in male flowers on all lines except 'Farbio'. The 500 ppm AgNO3 application yielded by far the most male flowers. The 300 ppm Ag(S2O3)2 treatment produced about half the number of male flowers of 300 ppm AgNO3. The 30 ppm GA-4/7 treatment gave few males and was definitely too low. The concentrations of Ag(S203)2 were not sufficient to induce a substantial number of male flowers on 'Farbio'. Several nodes appeared to have been induced partially but they quickly reverted to produce female flowers. Both AgNO3 applications hampered plant growth although neither extensive leaf crinkling nor necrosis was evident. Specifically, the plants in the 500 ppm AgNO3 treatment were several leaves behind in their development. This was more clearly demonstrated in a subsequent trial in early winter under very poor light conditions. Ten plants each of four varieties were treated in the first leaf stage with 2,000 ppm and 500 ppm AgNO3 and Ag(S203)2 respectively. Another set of the four varieties was similarly treated at the third leaf stage, about 10 days later.

The high concentration of AgNO3 proved disastrous at both treatment times. Plants became severely chlorotic and necrotic and none survived. The 500 ppm AgNO3 treatment resulted in crinkled leaves and poor plants but still a good number survived, mainly from the second treatment. All plants produced male flowers as expected. Both application times and both concentrations of Ag(S203)2 did not result in great damage to the plants. Some leaves were chlorotic at the edges with limited necrosis. All plants, however, grew out of this without a problem.

All plants of the first application time of Ag(S203)2 bore male flowers from the first node on while those of the late treatment possessed a variable number of nodes with female flowers. The treatment with 500 ppm AgNO3 resulted in approximately 2-3 weeks retardation of growth in comparison with check plants, whereas neither concentrations of Ag(S203)2 hampered plant growth.

Yield of male flowers thus appears to be lower after treatment with Ag(S203)2 but the chance of losing plants is also definitely less than when using AgNO3. In conditions of poor growth, the 'soft' treatment with Ag(S203)2 could thus be preferred over the 'hard' treatment with AgNO3.

Table 1. Number of male flowers per plant/Number of nodes with male flowers per plantz after treatment with various chemicals.

Variety

Treatment Chemical

Conc. in ppm

Al

A2

G6

'Farbio'

AgNO3

500

170/17

199/21

73/16

48/13

300

114/19

128/20

65/15

21/8

Ag(S2O3)2

100

28/6

50/5

9/1

0/0

150

21/7

38/8

22/8

1/1

300

54/11

45/8

24/6

1/1

2x100

36/6

48/5

15/3

1/1

2x150

36/7

89/11

35/9

1/1

GA-3

1500

25/7

98/13

40/11

5/3

GA-4/7

30

12/5

19/6

7/2

1/1

Water

1/1

0

0

0

z only the first 25 nodes considered.

Literature Cited

  1. Veen, H. and S. C. v.d. Geijn. 1978. Mobility and ionic form of silver as related to longevity of cut carnations. Planta 140:93-96.
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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