Cucurbit Genetics Cooperative Report 3:17-19 (article 10) 1980
Influence of Reciprocal Donor Scions on Fruit Setting
Characteristics of Recipient Scions of Cucumis sativus
and C. hardwickii R.
James Nienhuis and R. L. Lower
University of Wisconsin,
Madison, WI 53706
Cucumis sativus cultivars average approximately
1 1/4 marketable fruit per plant in once-over mechanically
harvested operations (5). Low fruit number per plant is
presumably due to the inhibitory effect of the seed development
of the first fertilized flower on the development of subsequently
pollinated fruit (4,8). There is speculation as to whether
the fruit setting mechanisms involve a translocated fruiting
inhibitor produced by the developing fruit, or if the developing
fruit set is precluded due to the limited availability of
substrates. The later hypothesis is supported by the observation
that in greenhouse seed production, multiples of seeded
fruit can be produced on C. sativus plants if pollination
is delayed until the plants are very large. The increased
photosynthesis are would be expected to produce more dry
matter and, hence, support a larger "sink" of
seeded fruit.
Horst and Lower (3) reported that C. hardwickii plants
set as many as 80 fruit per plant under North Carolina conditions.
Cucumis hardwickii plants have the ability to sequentially
set large numbers of fruits that weigh approximately 25-35
g each. Apparently in C. hardwickii, fruits with
developing seed do not inhibit later fertilized fruit as
is apparent in C. sativus cultivars.
Cucumis hardwickii plants are large (7.5 kg fresh
cut) compared to C. sativus cultivars (6). Also,
C. hardwickii is a short day plant with a critical
photoperiod of <12 hrs (2). The photoperiodic response
of may be a natural mechanism which delays fruit set until
photosynthetic are is maximized, analogous to the delayed
pollination of greenhouse seed production in C. sativus
cultivars. However, the reasons for the widely different
fruit setting behavior in the two species are unknown.
The objective of this experiment was to measure the relative
efficiency of grafted C. hardwickii and C.
sativus donor scions in supporting fruit on defoliated
recipient scions.
The experiment was conducted at the University of Wisconsin
Biotron from May to July, 1979. Two growth chambers were
programmed to provided similar environmental conditions: 30°C day/ 20°C night temperatures, 70% RH,
and approximately 500 µE m2 of light intensity at plant
height.
The graft combinations used were the following:
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Defoliated recipient scion
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| 1 |
Cucumis hardwickii |
Cucumis hardwickii |
(self-grafted) |
| 2 |
Cucumis sativus |
Cucumis hardwickii |
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| 3 |
Cucumis hardwickii |
Cucumis sativus |
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| 4 |
Cucumis sativus |
Cucumis sativus |
(self-grafted) |
The C. sativus cultivar used was the gynoecious
inbred Gy 14. The grafts were made approximately three
weeks after planting using a modified approach graft technique
similar to the one described by Denna (1). All the above
graft combinations were repeated using each species as rootstock.
No fruit were allowed to develop on the donor arms. The
recipient scions were defoliated ( by removing leaves as
they expanded) to make them primarily dependent upon the
donor scions for photosynthate. Pollinations were attempted
on all pistillate flowers available on the recipient scion.
The experimental design was a split plot using rootstocks
as main plots and graft combinations as sub-plots, with
six replications. Main plots (rootstocks) were non-significant
for all variables; therefore, the graft combinations were
averaged over both replications and rootstocks.
The dry and fresh weights of the C. sativus donor
scions were either not significantly different or less than
the C. hardwickii donor scions. However, fruit
number per plants was greater on both C. sativus and
C. hardwickii recipient scions when C. sativus
was used as donor scion than when C. hardwickii
was used as donor scion (Table 1). Also, fruit weight was
greater on the C. sativus recipient scions as donor
scion (Table 1). Neither dry weight (excluding fruit weight)
nor seed weight of the recipient scions were significantly
different regardless of donor scion.
The C. sativus recipient scions may more accurately
measure donor scion potential, as the increased fruit number
on C. hardwickii recipient scions may have been
a result of the increased frequency of pistillate flowers.
Previous studies (7) have demonstrated that gynoecious C.
sativus donor scions promote flowering, particularly
pistillate flowering, on C. hardwickii recipient
scions.
Although the weight of the C. sativus donor scions
was less than that of C. hardwickii donor scions,
they were able to support a greater "sink" of developing fruit. If fruit number and fruit weight on the
C. sativus donor scions reflects the amount of
photosynthate produced and translocated by the donor scion,
then C. sativus appears more efficient that
C. hardwickii.
Table 1. Graft combination means over reps and rootstocks for several vegetative and fruiting characteristics.
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Defoliated recipient scion
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z Dry weight of recipient vine excluding fruit weight.
y Mean separation by Duncan's multiple range test.
x LSD calculated by Waller-Duncan Bayesian K- ratio t-test.
Literature Cited
- Denna, D. W. 1973. J. Amer. Soc. Hort. Sci.
98: 602-604
- Horst, E. K. 1977. M.S. Thesis. Department of Horticulture,
North Carolina State University.
- Horst, E. K. and R. L. Lower. 1978. Cucumis hardwickii:
A source of germplasm for the cucumber breeder. Cucurbit
Genetics Coop. Rpt. 1:5.
- McCollum, J. P. 1934. Cornell Univ. Agr. Exp. Station
Memoir 163.
- Miller, C. H. and G. R. Hughes. 1969. J. Amer. Soc. Hort.
Sci. 94:485-487.
- Nienhuis, J. 1979. M.S. Thesis. Department of Horticulture,
North Carolina State University.
- Nienhuis, J. and R. L. Lower. 1979. Interspecific grafting
to promote flowering in Cucumis hardwickii. Cucurbit
Genetics Coop. Rpt. 2:11-12
- Tiedjens, A. A. 1928. J. Agr. Res. 36: 720-746.
