Cucurbit Genetics Cooperative Report 10:18-20 (article 13) 1987
Use of Silver Thiosulfate as a Potential Tool for
Testing Gynoecious Sex Stability in Cucumber (Cucumis sativus
Staub, J.E. and L. Crubaugh
U.S. Department of Agriculture, Agricultural Research Service and Department
of Horticulture, University of Wisconsin, Madison, WI 53706
Cucumber (Cucumis sativus L.) plants under stress. produce
more staminate flowers than those grown under optimal conditions (1,2,4,8).
For once-over mechanical harvest, processing cucumbers with uniform flowering
and concentrated fruit set are essential (5). Among the genetic manipulations
which has shown potential for increasing sex stability and uniform flowering
is the chracterization and introduction of the hermaphroditic character
(3). Hybrids made using hermaphrodites have been hypothesized to be sexually
more stable under conditions of environmental stress (7).
Recently improved pollen induction on gynoecious inbreds achieved by
using foliar applications of silver nitrate (9) or aminoethoxyvinylglycine
instead of gibberellic acid, has resulted in increased interest in using
gynoecious (G) x (G) hybrids. If hermaphroditic (H) pollen parents could
be developed which conferred adequate yield and quality, then a less-costly
pollen supply could be used in hybrid seed production. This and the fact
that G x H hybrids may be sexually more stable makes this an attractive
However, a consistent, rapid test for gynoecious sex stability has not
been developed. This has made identification of sex stable genotypes difficult,
and has been at least partially responsible for the lack of widespread acceptance
of the hermaphroditic character in plant breeding programs. Determining
whether silver thiosulfate could be used to identify plants which possessed
a more stable gynoecious character is thought to be desirable. If a dosage
could be identified which would provide a consistent stress threshold, then
rapid procedures might be developed for seedling screening for sex stability.
Naturally a prerequisite for such a procedure would necessitate that the
action of any chemical be unaffected by minor changes in the test environment
(photoperiod, temperature, relative humidity, etc.).
A series of experiments were designed to determine at what threshold
concentration and dosage silver thiosulfate would cause gynoecious genotypes
to produce staminate flowers. In the first experimental sequence, a dosage
of either 10 or 20 µl silver thiosulfate was administered at concentrations
of 6, 3, 1.5, and 0.75 mM to cotyledons of 7-day-old seedlings of the gynoecious
processing inbred line WI 1701 which had been germinated in pots 10 cm in
diameter. Treatments were arranged in a randomized complete block design
with 4 replications having 2 subsamples. Plants were grown to 10 flowering
nodes in a standard growing medium (2 soil: 1 sand: 1 peat: 1 perlite by
volume) in a greenhouse under a 16 hr. photoperiod at 25 to 28°C and
40 to 60% RH. The average quanta per day from solar radiation over 16 hrs.
during this experimental period ranged from 423 to 843 µmol s-1
m-2 and plants were supplemented by fluorescent lights (Sylvania
- F96Tl2/CW/VHO) providing approximately 40 µmol s-1 m-2
at the shoot apices to extend the photoperiod. Number of nodes with staminate
flowers were recorded. Based on these data, potentially effective concentrations
were isolated and used in 2 subsequent experiments where plants of WI 1701
were grown under similar environmental conditions as those described above,
except that the average solar radiation ranged from 240 to 281 µmol
Data suggest that 20 µl was a consistent, effective dosage for
the conversion of nodes to the staminate condition, except at 6mM (Table
1). The 20 µl dosage at 6 mM. was apparently above the threshold concentration
(Table 1, exp. 1), but elicited a response in a second series of experiments
(Table 2). Moreover, in the second series of experiments 1.5 mM at 20 µl
was not as effective as 6 mM. The lowest effective concentration was 0.75
mM. (Table 1, exp. 2).
One explanation which might account for disparities observed between
experiments was the difference in average quanta of solar radiation received
by the plants during experimentation. If this hypothesis is correct, then
effective threshold silver thiosulfate concentrations may vary and implementation
of this procedure for sex stability testing will require careful control
of environmental conditions.
Table 1. Mean percentage of staminate flowers after treatment of the
USDA processing cucumber inbred line WI 1701 with Ag(S2O3)2 at the cotyledon
z Plants treated at the cotyledons stage; approximately 7 days after
y 4 replications.
Table 2. Mean percentage of staminate flowers after treatment of the
USDA processing cucumber inbred line WI 1701 with Ag(S2O3)2at the cotyledon
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