Cucurbit Genetics Cooperative Report 5:12-13 (article 6) 1982
K. W. Owens and C. E. Peterson
University of Wisconsin, Madison, WI 53706
Two inbred backcross populations (2) were developed by crossing W1540, a small-fruited, gynoecious, determinate USDA breeding line with W1925 (Population I) and W1928 (Population II), both of which were large-fruited, monoecious and indeterminate. Two backcrosses were made to W1540, and the BC2 generation was selfed twice to produce BC2SC2 lines. Separate lines were maintained beginning at the BC1 generation and all generations were grown in the greenhouse with no conscious selection practiced at any stage in the procedure. 108 lines in Population I and 79 lines in Population II were evaluated for fruit length, sex type and growth habit in the field at Hancock, WI in 1981. A randomized complete block design with three replications and four plants per plot was used.
In the BC2SC2 generation, four homozygous classes were expected: gynoecious, determinate (FF, dede); gynoecious, indeterminate (FF, DeDe); monoecious, determinate (ff, dede); and monoecious, indeterminate (ff, DeDe). Lines segregating for one of the traits were excluded from the analysis. Expectations for these classes were calculated on the assumption of no linkage, and chi-square tests were performed to test for independence. In addition to looking at homozygous lines, individual plants were classified for sex type and growth habit so that the formation from segregating lines could be used for analysis of independence. The frequency distributions of fruit length were plotted for both populations and examined for association with sex type and growth habit.
Tests of independence of sex type and growth habit (using homozygous line data) were highly significant in both populations (Table 1). The fact that there was an excess of parental types and a deficiency of recombinant types suggests an association or linkage between the F gene, for female sex type, and the de gene, for determinate habit. The tests of independence of sex type and growth habit, using individual plant data, were also highly significant for both populations (Table 2), which further supports the hypothesis of linkage. These results are in agreement with Odland and Groff’s 1962 report (1) of linkage between growth habit and sex type in cucumber. The authors reported a 7.3% recombination value.
Unconscious selection against monoecious and determinate types probably occurred in both populations. This would explain the unequal numbers of recombinant types recovered (Table 2). No recombination values can be calculated during the inbred backcross approach. Since recombinant phenotypes were recovered, the linkage apparently is not tight.
From the analysis of the frequency distributions of fruit length in Populations I and II, there also appears to be an association of both sex type and growth habit with fruit length. Those lines homozygous for monoecious sex type (ff) and/or indeterminate growth habit (DeDe) had greater fruit length.
Table 1. Chi-square test of independence of sex type and growth habit in inbred backcross lines (Population I and II).z
Population I |
Population II |
|||||
Class |
Obs |
Expt. |
X2y |
Obs. |
Expt. |
X2y |
| FF, dede | 92 | 82.78 | 0.9184 | 69 | 62.09 | 0.6627 |
| FF, DeDe | 2 | 6.24 | 2.2373 | 1 | 4.77 | 2.2450 |
| ff, dede | 0 | 6.24 | 5.2750 | 0 | 4.77 | 3.8261 |
| ff, DeDe | 2 | 0.49 | 2.0869 | 2 | 0.37 | 3.4962 |
| 96 | 96 | 10.5176** | 72 | 72 | 10.230** | |
z Data on BC2S2 lines homozygous for both loci.
y Using Yates correction for continuity.
** Significant at .01 level.
Table 2. Chi-square test of independence of sex type and growth habit in inbred backcross individuals (Population I and II).
Population I |
Population II |
|||||
Class |
Obs. |
Expt.z |
X2 |
Obs. |
Expt.z |
X2 |
| FF, dede | 1038 | 986.55 | 2.683 | 776 | 729.96 | 2.904 |
| FF, DeDe | 83 | 134.44 | 19.685 | 33 | 79.04 | 26.818 |
| ff, dede | 4 | 55.44 | 47.733 | 9 | 55.04 | 38.512 |
| ff, DeDe | 59 | 7.56 | 350.250 | 52 | 5.96 | 355.651 |
| 1184 | 1184 | 420.351** | 870 | 870 | 423.88** | |
z Expectations calculated from marginal frequencies because of disturbed segregation observed for single genes.
**Significance at .01 level.
Literature Cited
- Odland, M.L., and D.W. Groff. 1962. Linkage of vine type and geotropic responses with sex forms in cucumber, Cucumis sativus L. Proc. Amer. Soc. Hort. Sci. 82: 358-369.
- Wehrhahn, C. and R.W. Allard. 1965. The detection and measurement of the effects of individual genes in the inheritance of a quantitative character in wheat. Genetics 51: 109-119.