Cucurbit Genetics Cooperative Report 6:27-28 (article 14) 1983
O. M. B. de Ponti, G. G. Kennedy, and F. Gould
Institute for Horticultural Plant Breeding, P.O. Box 16, 6700 AA Wageningen, The Netherlands (first author); North Carolina State University, Raleigh, NC 27650 (second and third authors)
Opinions on the relation between the bitter principle cucurbitacin-C and resistance to the spider mite Tetranychus urticae are not unanimous. North American authors as DaCosta and Jones (1) and Gould (2) hypothesized a causal relation between bitterness and resistance to T. urticae, whereas in Europe, de Ponti (3) hypothesized only a genetic relation in terms of linkage of genes for resistance and bitterness.
In accordance with the latter hypothesis, de Ponti (4) succeeded in selecting some non-bitter lines whose resistance approached that of their bitter progenitors (Table 1). These lines were selected both in climate rooms, measuring oviposition of the spider mite; and in the glasshouse on hydroponics, measuring the development of damage on a scale of 0 to 5 after artificial infestation with 10 female mites per plant.
Table 1. Comparison of two glasshouse tests in the Netherlands and a field test in North Carolina (USA) for resistance of cucumber to T. urticae. Only the final observation is listed. Damage ratings are recorded on a scale of 0 (no damage) to 5 (maximal damage).
Damage Rating |
||||
Cultivar or line |
Bitterness |
1981 |
1982 |
1982 |
| G6 | – | 3.8 a | 4.1 a | 3.9 a |
| F6 (H x R) | + | 1. 6 b | 2.0 b | 0.5 c |
| F5 (H x V) | + | 1.5 b | 1.6 b | 0.3 c |
| F5 (G6 x F5 (H x V)) | – | 1.9 b | 1.9 b | 3.3 a |
| F3 (G6 x F3 (H x V x H x R)) | – | 1.8 b | 2.5 b | 3.9 a |
| Calypso | + | 1.1 c | ||
| Marketmore 76 | + | 2.1 b | ||
| Marketmore 80 | – | 3.4 a | ||
G6 = susceptible check; H = Hybrid long green pickle; V = Varamin; R = Robin 50.
Figures followed by the same letter do not differ significantly from one another at the 5% level.
During the sabbatic leave of de Ponti at the NCSU Department of Entomology, we studied the performance of these resistant lines under field conditions at a location in Chowan County, North Carolina with a known high natural population of T. urticae.
During the field test in May through July 1982 conditions were dry, hot and windy, totally different from the glasshouse environment in the Netherlands. Damage ratings were scored as described for the glasshouse test. Both in the Netherlands and the United States, randomized designs were used with 7 and 4 repetitions respectively.
The resistance of the bitter lines was consistent, independent of location. In the United States the difference between the resistant lines and the susceptible check, G6, was even larger than in the Netherlands. The non-bitter resistant lines selected in the Netherlands, however, show hardly any resistance in the United States. From the present data, it is difficult to conclude whether that was due to differences in the environment, in the mite population, or both. In fact, these data support the earlier mentioned hypothesis of a causal relation between resistance and bitterness. We have to keep in mind that the described conditions in North Carolina are generally considered as promoting the formation or accumulation of cucurbitacins in plant tissues. Further investigations, mainly in the Netherlands, will try to clarify these contradictions, the more so as the reduction in resistance of one of the non-bitter lines in 1982 compared to 1981 is somewhat alarming, The possibility that there exists two different types of mite resistance in cucumber must certainly be considered.
Literature Cited
- DaCosta, C. P. and C. M. Jones. 1971. Cucumber beetle resistance and mite susceptibility controlled by the bitter gene in Cucumis sativus L. Science 172:1145–1146.
- Gould, F. 1978. Resistance of cucumber to Tetranychus urticae: Genetic and environmental determinants. J. Econ. Ent. 71:680–683.
- Ponti, O.M.B. de. 1980. Resistance in Cucumis sativus L. to Tetranychus urticae Koch.7. The inheritance of resistance and bitterness and the relation between these characters. Euphytica 29:513–523.
- Ponti, O.M.B. de. 1982. Plant resistance to insects: a challenge to plant breeders and entomologists, In: J. H. Visser and A. K. Minks (ed.), Proc. 5th Int. Symp. Insect-Plant Relationships Wageningen. Pudoc, Wageningen: 337–347.