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Cucurbit Genetics Cooperative Report 6:22-23 (article 11) 1983

Results of Linkage Studies and the Need for a Cooperative Effort to Map the Cucumber Genome

A.P.M. den Nijs and I. W. Boukema

Institute for Horticultural Plant Breeding, P. O. Box 16, Wageningen, The Netherlands

Since the first comprehensive compilation of the genes of the Cucurbitaceae (1), several additions have been published by the Cucurbit Gene List Committee of the Cucurbit Genetics Cooperative (CGC). Last year the total number of identified genes of the cucumber stood at 80 and several new ones were described in CGC Report No. 6. However, data on linkage relationships of these genes are still scant and scattered, although the cucumber with only seven chromosomes offers ample opportunity for linkages (much to the annoyance of many breeders).

There is an urgent need for compiling all available linkage data, and adding new results in order to increase our knowledge about the cucumber genome. In addition to this, linkage groups need to be identified with specific chromosomes, for example by analysis of trisomics.

In Table 1, some new recombination percentages are reported for four pairs of genes used in research at the IVT. Linkage tests according to Strickberger (2) showed that glabrous (gl) and divided leaf (dvl) are weakly linked (recombination percentage 40%). The gene-pair dvl and resistance to scab (Ccu) segregated significantly different from the expected 9:3:3:1 ratio, but the recombination was estimated as 46%. The two genes are, therefore, virtually independent. Also, the genes gl and bitterfree (bi) behaved independently with a non-significant deviation from the expected ratio. The genes bi and dvl also segregated independently. Deviations from the 3:1 ratio for some of the dvl segregations indicated that this marker gene could not always be reliably identified at the seedling stage. Further classifications with this mutant will be made in a later growth stage on the basis of the typical corolla shape as well as the leaves. The gene appears to be very lightly linked to a locus governing determinate growth.

More intimate knowledge of the genome of a species has greatly stimulated breeding research in several crops, and it also seems to play an important role in choosing model plants for novel plant breeding techniques. Tomato, petunia and pea appear to be favored for genetic engineering research in horticultural crops. Cucumber is an important crop as well, but with many problems still to be solved.

We propose that the CGC extend the effort started by the Gene List Committee and compile and publish a provisional linkage map of the cucumber. Further studies on linkage must be stimulated and possibly coordinated to avoid duplication and to ensure the fastest progress.

Table 1. Recombination percentage (%), size of F2 populations for linkage tests (N), and calculated chi-square ratios for the 9:3:3:1 ratios (X2) for four pairs of genes.

Gene pair

%

N

X2

dvl / gl

40

247

9.13*

dvl / bi

50

249

3.62 

dvl / Ccu

46

223

6.56*

gl / bi

44

330

4.85 

*Significant at P = 0.05

Literature Cited

  1. Robinson, R. W., H. M. Munger, T. W. Whitaker and G. W. Bohn. 1976. Genes of the Cucurbitaceae. HortScience 11:554–568.
  2. Strickberger, M. W. 1968. Genetics. The MacMillan Co., New York, 868 pp.
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