Cucurbit Genetics Cooperative Report 15:54 (article 19) 1992
Bitterness in Snake Cucumber Cucumis melo var. flexuosus Naud.
Hanan S. Elawed and Ali E. El Jack
Ministry of Agriculture, Khartoum, Sudan; Department of Horticulture, University of Gezira, Wad Medani, Sudan
The immature fruit of the Snake cucumber is a popular salad and pickling crop in the Sudan. Bitter fruits are occasionally discovered in the produce, and although in very small quantities, it is sufficient to discourage sales and reduce prices of a specific lot. This study was conducted to investigate the phenomenon so as to enable selection for non-bitterness prior to fruiting.
Seed of a local variety of snake cucumber was obtained from a local seed dealer at Wad Medani. Evaluation for bitterness in mature plants was done by testing a small part of a mature leaf blade, petiole, stem, and fruit. Dry seeds were evaluated after removal of the seed coat. Germinated seeds were evaluated by testing the unfolding cotyledons. Seedlings were evaluated at the cotyledon, first, and second leaf stages (5). Thin layer chromatography (TLC) was used to determine the bitter principle in bitter fruits.
When individually evaluating 2400 mature plants, it was observed that plants with bitter fruits also had bitter leaves and stems. This relationship can be exploited to select for non-bitter lines. Of the 2400 mature plants tested, 8 were highly bitter (0.3%), 14 were slightly bitter (0.6%), two relatively sweeter in taste (0.08%) and the rest had the normal, non-bitter taste. Non-bitterness has been reported to impart resistance to cucumber beetles (1, 4, 6) but it may result in susceptibility to other insects such as two spotted spider mites (2). A study of the inheritance of this trait is planned as it has been reported to be relatively simple (1, 4, 6).
In a nursery experiment in which approximately 1000 seedlings were evaluated individually by tasting the cotyledon, about 100 germinating plants (10%) were bitter. The same plants were evaluated a week later by tasting the first leaf and only five seedlings (0.5%) expressed bitterness. In another experiment in which plants were evaluated at the second leaf stage, 5 seedlings out of 450 (1.1%) were bitter. It has not been determined whether the seedlings will maintain the bitterness through fruiting. Thus it is suggested that evaluation be delayed at least until the first or second leaf stage.
One thousand of the dry seeds were evaluated individually and none gave the bitter taste. When another thousand seeds were germinated, 24 out of 230 (10%) germinating seeds had a bitter taste. It seems that the bitter principle develops after seed germination, soon reaches a maximum, followed by a substantial reduction at the first and second leaf stages and a gradual reduction up to maturity. The bitter principle was detected to be a triterpene (cucurbitacin).
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