Influence of Reciprocal Donor Scions on Fruit Setting Characteristics of Recipient Scions of Cucumis sativus and C. hardwickii R.

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Cucurbit Genetics Cooperative Report 3:17-19 (article 10) 1980

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.

Table 1.  Graft combinations used in this experiment.

Vegetative donor scion

Defoliated recipient scion
1 Cucumis hardwickii Cucumis hardwickii (self-grafted)
2 Cucumis sativus Cucumis hardwickii
3 Cucumis hardwickii Cucumis sativus
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. sativusdonor scions reflects the amount of photosynthate produced and translocated by the donor scion, then C. sativus appears more efficient that C. hardwickii.

Table 2. Graft combination means over reps and rootstocks for several vegetative and fruiting characteristics.

Donor scion

Recipient scion

Vegetative donor scion

Defoliated recipient scion
Dry wt (g)
Fresh wt (g)
Fruit No.
Fruit wt (g)
Dry wt (g)z
Seed wt (g)y
C. hardwickii C. hardwickii 49.7 394.4 1.1 21.3 13.8 13.8 A
C. sativus C. hardwickii 36.1 266.1 4.5 111.9 9.7 9.7 AB
C. hardwickii C. sativus 30.4 229.3 1.3 753.3 7.6 7.6 B
C. sativus C. sativus 27.1 210.2 2.4 2017.9 9.0 9.0 AB
LSD .05 5.6x 57.3x 1.0x 1217.4x 5.6x

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

  1. Denna, D. W. 1973. J. Amer. Soc. Hort. Sci. 98: 602-604
  2. Horst, E. K. 1977. M.S. Thesis. Department of Horticulture, North Carolina State University.
  3. Horst, E. K. and R. L. Lower. 1978. Cucumis hardwickii: A source of germplasm for the cucumber breeder. Cucurbit Genetics Coop. Rpt. 1:5.
  4. McCollum, J. P. 1934. Cornell Univ. Agr. Exp. Station Memoir 163.
  5. Miller, C. H. and G. R. Hughes. 1969. J. Amer. Soc. Hort. Sci. 94:485-487.
  6. Nienhuis, J. 1979. M.S. Thesis. Department of Horticulture, North Carolina State University.
  7. Nienhuis, J. and R. L. Lower. 1979. Interspecific grafting to promote flowering in Cucumis hardwickii. Cucurbit Genetics Coop. Rpt. 2:11-12
  8. Tiedjens, A. A. 1928. J. Agr. Res. 36: 720-746.