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Cucurbit Genetics Cooperative Report 2:11-12 (article 7) 1979

Interspecific Grafting to Promote Flowering in Cucumis hardwickii

J. Nienhuis and R. L. Lower

University of Wisconsin, Madison, WI 53706

D. M. Pharr

North Carolina State University, Raleigh, NC 27650

Cucumis hardwickii Royle is thought to be either a feral or progenitor species of the cultivated cucumber, C. sativus L. It is currently being evaluated in our breeding program as a potential source of variability for several horticulturally important characteristics (2). However, our strain of C. hardwickii is a short day plant which flowers only when the photoperiod is less than 12 hours at 30°C day / 20°C night temperatures (2). The short day nature of C. hardwickii has restricted its use in genetic studies as well as in population development by random mating in the field.

In many plant species, grafting has been used as a tool to promote flowering in varieties which would not flower in specific environments. Lang (3) recently reviewed the work of numerous authors who investigated the transfer of flowering promoters from induced to non-induced scions by grafting between varieties as well as species. In Cucurbitaceae, there are also examples of flowering promotion and changes in sex expression as a result of grafting (1, 4).

The objectives of this investigation were: 1) to study the effects of grafts using gynoecious and monoecious C. sativus cultivars on the flowering response of C. hardwickii recipient scions and 2) to observe the effect of defoliation of the recipient scions.

This study was undertaken at the Southeastern Plant Environmental Laboratory in Raleigh, NC from June to September 1978. Growth chambers were programmed to provide similar environmental conditions for all factors other than photoperiod. Both a 9 hour inductive and a 15 hour non- inductive photoperiod at 30°C day / 20°C night temperatures were used. The grafting method was an approach graft technique similar to that described by Friedlander et al. (3). Treatments consisted of a non-grafted C. hardwickii check plus C. hardwickii recipient scions grafted onto three donor scions: C. hardwickii and two C. sativus cultivars 'Addis' (monoecious) and 'Gy14' (gynoecious). Within each graft combination, four of the replications had their recipient arms defoliated and the other four remained vegetative. In all cases, the rootstock corresponded to the donor scion.

In the inductive photoperiod (9 hours), the graft combinations resulted in no significant change from the normal flowering characteristics of the check and self- grafted C. hardwickii recipient scions.

In the non-inductive photoperiod (15 hours), both the gynoecious and the monoecious C. sativus donor scions resulted in increased total flowers/day and increased pistillate flowers/day on C. hardwickii recipient scions (Table 1). Within each graft combination, there was no significant difference between vegetative and defoliated scions; however, the number of pistillate flowers generally increased on the defoliated scions (Table 1). The check and self-grafted C. hardwickii recipient scions did not initiate flowering until approximately 65 days after planting, whereas flowering was initiated after approximately 45 days when either C. sativus cultivar was used as a donor scion.

In other studies, C. hardwickii has been successfully approach grafted onto both 'Addis' and 'Gy14' under field conditions (unpublished data). It is, therefore, possible to induce C. hardwickii to flower under long day conditions in the field using either monoecious or gynoecious C. sativus donor scions. By grafting C. hardwickii onto gynoecious C. sativus donor lines, random F1 hybrids could be produced to initiate a breeding population.

Table 1. Effect of various graft combinations of gynoecious and monoecious C. sativus donor scions on the flowering response of C. hardwickii recipient scions.

Donor scion

C. hardwickii recipient scion

Total flowers/day

Pistillate flowers/day

C. hardwickii

check; non-grafted

1.94

.06

C. hardwickii

vegetative

1.48

0

C. hardwickii

defoliated

.19

0

Addis (C. sativus)

vegetative

4.10

.31

Addis (C. sativus)

defoliated

5.44

.96

Gy14 (C. sativus)

vegetative

4.94

.33

Gy14 (C. sativus)

defoliated

6.69

1.42

 

LSD .05

1.92

1.25

Literature Cited

  1. Friedlander, M., D. Atsmon, and E. Galun. 1977. The effect of grafting on sex expression in cucumber. Plant and Cell Physiol. 18:1343-1350.
  2. Horst, E. K. and R. L. Lower. 1978. Cucumis hardwickii: A source of germplasm for the cucumber breeder. Cucurbit Genetics Coop. Rpt. No. 1. North Carolina State University, Raleigh, NC.
  3. Lang, A. 1965. Physiology of Flower Initiation. Encyclopedia of Plant Physiology 15:1380-1536. W. Ruhland, ed.
  4. Nienhuis, J. and A. M. Rhodes. 1977. Interspecific grafting to enhance flowering in wild species of Cucurbits. HortScience 12:458-459.
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