Cucurbit Genetics Cooperative Report 2:6-7 (article 3) 1979
o. M. B. de Ponti
Institute for Horticultural Plant Breeding, Wageningen, The Netherlands
Based on a thorough study of the host-parasite relationship using cucumber varieties with different levels of resistance to the twospotted spider mite, two resistance tests were developed: a laboratory test (1) measuring acceptance and reproduction and a practical test (2) measuring damage as criteria of resistance.
After a first screening of 800 varieties from the IVT Cucumis sativus L. collection, the 50 least damaged varieties were extensively retested in laboratory and practical tests (2). Nine varieties (from 800) were significantly different from the susceptible control for acceptance, reproduction, and damage index (2).
The reduction in reproduction after moving the mites from a susceptible variety, on which they are normally reared, to other (resistant) varieties might only be of a temporary nature. In that case, the resistance of the selected varieties would not be genuine. To investigate this, both resistance tests were repeated after the mites had been reared on the selected varieties for 10 to 20 generations. The degree of acceptance and reproduction and the damage index decreased rather than increased, providing evidence for the genuineness of the resistance (3).
To increase the level of resistance found in the partially resistant varieties, these varieties have been intercrossed and the successive generations subjected to selection in laboratory and practical tests. A number of F5-lines have been selected with a markedly lower mite reproduction than the parental varieties (Table 1). The 15 most resistant lines were released in 1978 to private breeding firms in the Netherlands. They will attempt to combine this resistance with other important horticultural characters to develop high standard twospotted spider mite resistant varieties.
It is not surprising that all resistant varieties are bitter because the world collection of cucumber contains 99% bitter varieties. Although we found that resistant and bitter varieties generally do not contain more cucurbitacin- c than susceptible and bitter ones, we noticed an unintended increase in the amount of cucurbitacin-C in the selected F5-lines compared with the parental varieties. On the other hand, many bitterfree and resistant plants were found in F2 and backcross generations after crossing resistant and bitter with susceptible and bitterfree lines.
Table 1. Degree of acceptance and reproduction of the twospotted spider mite on a susceptible control, on 2 partially resistant cucumber varieties, and on 2 lines derived from crosses between these varieties.
Variety or line |
Acceptance (%) |
Reproduction (eggs/female, 3 days) |
| ‘Hybrid LGP’ | 36 | 14.1 |
| ‘Robin 50’ | 45 | 15.1 |
| F5 (‘HLGP’ x ‘Robin 50’) | 45 | 8.4 |
| F5 (‘HLGP’ x ‘Robin 50’) | 34 | 9.4 |
| Susceptible control | 72 | 21.0 |
Literature Cited
- de Ponti, 0. M. B. 1977. Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 2. Designing a reliable laboratory test for resistance based on aspects of the host-parasite relationship. Euphytica 26:641-654.
- de Ponti, 0. M. B. 1978a. Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 3. Search for sources of resistance. Euphytica 27:167-176.
- de Ponti, 0. M. B. 1978b. Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 4. The genuineness of the resistance. Euphytica 27:435-439.