Cucurbit Genetics Cooperative Report 5:2-3 (article 1) 1982
P. T. Della Vecchia, C. E. Peterson, and J. E. Staub
University of Wisconsin, Madison, WI 53706
Since Horst and Lower (1) first reported on the potential of Cucumis sativus var. hardwickii (R.) Alef. as a possible source of germplasm for increasing yield in pickling cucumbers, there has been considerable interest by both public and private cucumber breeders in the exploitation of ‘hardwickii’ types. Potentially the most useful characteristic of ‘hardwickii’ types is their ability to sequentially set a large number of seeded fruits per plant. They also differ from C. sativus in several other morphological and flowering characteristics. ‘Hardwickii’ types are facultative short-day plants with respect to flowering. This short-day requirement for early flowering has restricted their use in genetic studies and population development, especially under field conditions at high latitudes. The objective of this study was to investigate the effect of the duration of short-day treatments on the flowering response of a ‘hardwickii’ line (PI 215589).
The experiment was conducted in the greenhouse at Madison, WI, from June to August, 1981. Photoperiod was conducted in the greenhouse a Madison, WI, from June to August, 1981. Photoperiod was controlled by a dark chamber built on a greenhouse bench. Plants of the ‘hardwickii’ line were grown under 10 hr photoperiod for 0, 5, 10, 15, and 20 days, the short-day condition being imposed after the cotyledons expanded. Treatments were replicated 4 times, with 2 plants per plot. AFter the short day treatment, plants were moved to an adjacent greenhouse bench and grown under 16 hr photoperiod. Fluorescent lights (Sylvania F96T12/CW/VHO), providing approximately 6,000 lux at the shoot apices, were used to extend the photoperiod to 16 hr. Greenhouse temperature was not controlled. Maximum and minimum temperature monitored daily for each photoperiod regime were very similar, ranging from 17 to 35°C. The effect of the duration of short day treatments on the flowering response was measured as the node number of the first flower on the main stem (node of the first flower) and number of days from germination to anthesis of the first flower on the main stem (days to first flower). The treatment x replicate mean squares were used as an estimate of the experimental error.
Mean values for node of the first flower and days to first flower are presented in Table 1. Five days under a 10 hr photoperiod were enough to lower the node of the first flower from approximately the 14th to the 5th node. Exposure to the short-day treatment for more than 10 days resulted in practically no additional response in terms of the node number at which the first flower appeared. In contrast, additional periods of time under short day treatments significantly decreased days to first flower. This phenomenon is commonly observed in a large number of photoperiodic plants (2).
Nienhuis and Lower (3) successfully used grafting techniques to induce early flowering under field conditions in the ‘hardwickii’ derived line ‘LJ 90430’. If the photoperiodic response observed in the present study is true of other late flowering ‘hardwickii’ and C. sativus accessions, then short day treatment can be as effective as grafting. Since ‘hardwickii’ plants can be induced to flower earlier by as little as give days under short photoperiod, seedlings could be exposed to the short-day treatment before being transplanted to the field.
Table 1. Mean values of node of the first flower (NNFF) and days to first flower (NDFF) for PI 215589 plants grown under short (10 hr) photoperiod for different number of days.
No. of days under short photoperiod |
No. of plants observed |
NNFF |
NDFF |
| 0 | 8 | 13.63 | 54.00 |
| 5 | 8 | 4.00 | 42.88 |
| 10 | 8 | 3.13 | 38.38 |
| 15 | 8 | 2.88 | 34.25 |
| 20 | 8 | 2.88 | 32.63 |
| LSD (0.01) | 1.09 | 2.56 | |
| CV % | 8.76 | 3.08 |
Literature Cited
- Horst, E. K. and R. L. Lower. 1978. Cucumis hardwickii: A source of germplasm for the cucumber breeder. Cucurbit Genetics Coop. Rpt. 1:5.
- Lang, A. 1965. Physiology of flower formation. Vol XV(1): p. 1380-1536. In W. Ruhland (ed.) Encyclopedia of Plant Physiology. Springer-Verlag, New York.
- Nienhuis, J. and R. L. Lower. 1979. Interspecific grafting to promote flowering in Cucumis hardwickii. Cucurbit Genetics Coop. Rpt. 2:11-12.