Cucurbit Genetics Cooperative Report 5:4-5 (article 2) 1982
P. T. Della Vecchia, C. E. Peterson and J. E. Staub
University of Wisconsin, Madison, WI 53706
Cucumis sativus var. hardwickii (R.) Alef. has been suggested as a possible source of germplasm for increasing yield in pickling cucumbers (1). Potentially the most useful characteristic of ‘hardwickii’ types is their ability to sequentially set a large number of seeded fruits per plant. The exact mechanism by which this is accomplished is still unknown. Horst and Lower (1) suggested that in the ‘hardwickii’ types, unlike the commercially grown C. sativus cultivars, fruits with developing seeds do not inhibit set and development of additional fruits. ‘Hardwickii’ types are facultative short-day plants with respect to flowering. Nienhuis and Lower (2) suggested that this photoperiodic response to flowering could be involved in the yield capacity of ‘hardwickii’ plants. By delaying flowering and fruit set, a large leaf area can be attained which could support high fruit yields.
The object of this investigation was to study the inheritance of short-day response to flowering in crosses between a short-day ‘hardwickii’ line (PI 215589) and unrelated day-neutral C. sativus lines. This should provide some basic information for further investigations of the relationship of flowering and yield in the ‘hardwickii’ types
In order to study the inheritance of short-day response to flowering the following crosses were made: Cross I – W1606 x PI 215589; Cross II – W1909 x PI 215589; Cross III – W1548 x PI 215589. W1606 and W1909 are typical U.S.A. pickling and slicing cucumbers, respectively. W1548 is a long-fruited line selected from a recent plant introduction from the People’s Republic of China. F1s were selfed and backcrossed to the respective parental lines in order to produce F2 and BC1 progenies for each cross. Parental lines, F1, F2, and BC1 generations of Crosses I, II, and III were grown under long days (16 hr) in greenhouses at Arlington, WI during the summers of 1980 and 1981. Fluorescent lights (Sylvania 96T12/CW/VHO), providing approximately 7,500 lux at the shoot apices, were used to extend the photoperiod to 16 hr. The greenhouse temperature ranged from 20o to 35o. Plants were arranged on benches in a randomized complete block design with 3 replications. Each replication consisted of the following number of plants per generation: F1and parental lines, 4 plants each; BC1 generations, 12 plants each; F2 generations, 28 plants. Data on the photoperiodic responses were node number of the first flower on the main stem (NNFF). Plants were further classified as early (NNFF < 5) or late (NNFF > 11) flowering.
The phenotype of F1 and BC1P1 plants for all crosses was similar to the early flowering parent (P1) Frequency distributions of NNFF for F2 and BC1 P2generations for all crosses showed clear-cut segregation of early and late flowering plants in approximate 1:1 and 3:1 ratios, respectively. A combined Chi-square test for the segregation data is presented in Table 1. A good fit to the expected genetic ratios supports the hypothesis that the short day requirement for early flowering in this ‘hardwickii’ line (PI 215589) is determined by a single recessive gene. A preliminary allelism test indicates that this recessive gene is most likely allelic to the previously reported df recessive mutant for the delayed flowering phenotype in cucumber (3).
Table 1. Number of early and late flowering plants in the parental lines, F1, F2, and backcross generations of Crosses I, II, III grown under 16 hr photoperiod in greenhouses at Arlington, WI, in 1980 and 1981.z
Generation |
No. plants early floweringy |
No. plants late floweringw |
Expected ratio |
Chi-square |
P |
| P1: W1548 | 36 | – | – | – | – |
| P1: W1606 | – | – | – | – | |
| P1: W1909 | – | – | – | – | |
| F2: PI 215589 | – | 36 | – | – | – |
| F1 | 36 | – | – | – | – |
| BC1P1 | 108 | – | 1:0 | 0.00 | 1.00 |
| BC1P2 | 53 | 55 | 1:1 | 0.04 | 0.75-0.90 |
| F2 | 196 | 56 | 3:1 | 1.04 | 0.25-0.50 |
z Populations were combined for segregation analysis based on test of homogeneity.
y Early flowering: NNFF ≤ 5.
w Late flowering: NNFF ≥ 11.
Literature Cited
- Horst, E. K. and R. L. Lower. 1978. Cucumis hardwickii: A source of germ-plasm for the cucumber breeder. Cucurbit Genetics Coop. Rpt. 1:5.
- Nienhuis, J. and R. L. Lower. 1980. Influence of reciprocal donor scions on fruit setting characteristics of recipient scions of Cucumis sativus and C. hardwickii R. Cucurbit Genetics Coop. Rpt. 3:17-18.
- Shifriss, O. and W. L. George, Jr. 1965. Delayed germination and flowering in cucumbers. Nature 206:424-425.