Cucurbit Genetics Cooperative Report 6:8-9 (article 4) 1983
H. Inggamer and O.M.B. de Ponti
Institute for Horticultural Plant Breeding, P.O.B. 16, 6700 AA Wageningen, The Netherlands
In order to improve the biological control of the glasshouse whitefly (Trialeurodes vaporariorum) with the parasitic wasp Encarsia formosa, glabrous cucumber mutants were introduced from the USSR and the USA (1). The glabrousness of all mutants investigated was governed by the same recessive gene gl (2).
The general horticultural value of the glabrous lines was improved by repeated backcrossing of one of the Russian mutants (Odnostebelnyi 33) with a Dutch glasshouse cucumber variety. Some negative qualities found in all mutants, such as frizzled leaves with pinpoint necrotic spots, stress sensitivity, and poor root systems were persistent despite rigid selection. This approach was, therefore, abandoned after we found an interesting alternative.
During our backcross program we got the impression that heterozygous (Glgl) plants were less hairy than homozygous plants. To verify this, 10 randomly chosen plants of two backcross populations (A and B) were investigated in detail. The lower sides of comparable leaves were dusted with green fluorescent powder and the hairs of two leaf areas of 12.5 mm2 were counted by two independent observers using a binocular microscope. The zygosity of the chosen plants was checked by selfing each plant and observing possible segregations in the progeny. Both of the B1.1 populations (A and B) happened to contain 50% heterozygotes, which carried about half the number of hairs of that of the GlGl homozygotes. From these data we concluded that the gl gene is inherited in an intermediary way. The variation around the mid-parent value was considered non-heritable.
In laboratory and glasshouse studies the possible advantage of hybrids with only half the number of hairs for the mobility and, thus, for the parasitizing efficiency of Encarsia formosa (1), will be investigated. The horticultural value of these hybrids was comparable to that of the pubescent parent without any of the above-mentioned negative qualities of the glabrous mutants. It seems, therefore, that those other characters are not inherited in an intermediary fashion.
Table 1. Average numbers of hairs per 12.5 mm2 on the lower leaf surface of homozygous and heterozygous B1.1 plants (4 counts/plant).
Generation |
Genotype |
Number counted |
Average number of hairs |
Range of the means per plant |
| P1 (pubescent) | GlGl | 3 | 42 | 41 – 44 |
| B1.1A | GlGl | 5 | 45 | 39 – 49 |
| Glgl | 5 | 23 | 18 – 29 | |
| B1.1B | GlGl | 5 | 47 | 39 – 51 |
| Glgl | 5 | 22 | 19 – 27 |
Literature Cited
- Ponti, O.M.B. de. 1979. Breeding glabrous cucumber varieties to improve the biological control of the glasshouse whitefly. Cucurbit Genetics Coop. Rpt. 2:5.
- Inggamer, H. and O.M.B. de Ponti. 1980. The identity of genes for glabrousness in Cucumis sativus L. Cucurbit Genetics Coop. Rpt. 3:14.