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Cucurbit Genetics Cooperative Report 6:75-76 (article 38) 1983

Intense Bitterness in Commercial Zucchini

Mark E. Herrington

Redlands Horticultural Research Station, Ormiston, Qld. 4163, Australia

Twenty-two cases of food poisoning associated with intensely bitter zucchini were recorded by Queensland health authorities between November, 1981 and December, 1982.

In case studies symptoms of illness were apparent 1 to 2 hours after consumption. Ingestion of about 3 g of bitter zucchini was sufficient to incite nausea followed by collapse, with severe stomach cramps lasting 3 days, and diarrhea which persisted longer. Vomiting was seldom associated. The extremely unpleasant taste penetrated entire meals and usually prevented ingestion. However, mastication of affected fruit or swallowing small amounts of associated vegetable was often sufficient to produce diarrhea and less frequently, stomach cramps.

Complaints were traced back through the marketing chain to identify the cause. Although environmental conditions are known to promote bitterness in cucumbers (1), no conditions were consistently implicated with zucchini. The cultivar Blackjack was in production on all 20 farms identified in initial successful tracebacks and was the only cultivar being grown on 16 of these farms.

'Blackjack' has been the main cultivar grown in Queensland for 10 years. However, one traceback has now also implicated 'Castle Verde'.

Plants producing bitter fruit are apparently rare in commercial zucchini crops and we are unaware of their occurrence elsewhere. Examination of up to 2000 plant samples in commercial plantings which were the source of bitter fruit in consumer samples has failed to isolate “bitter” plants.

A single plant producing intensely bitter fruit was identified in a commercial zucchini crop not involved in poisoning complaints. The cultivar used, while producing dark green fruit, is uncertain. Selfings were not successful. However, seed produced by open-pollination was collected from this plant and 36 progeny evaluated.

The progeny was considered a backcross and plants segregated, 20 producing bitter fruit to 16 producing non-bitter fruit. This is consistent with the single dominant gene hypothesis for bitterness (2) (chi square = 0.44, P = 0.52). At early anthesis bitterness of the leaf (detectable only at the junction of petiole and lamina) exactly corresponded with bitterness of fruit.

Although the field-identified bitter zucchini plant had more silvering, lighter green colored immature and yellow mature fruit, and had shorter fruit, there were no good associations between these characters and bitterness in its progeny. Selfings and outcrossing are being carried out on selected plants.

Cucurbitacin E., Cuc. I and Cuc. E-glycoside have been identified in extracts from samples of bitter fruit.

The results confirm the intense bitterness in commercial zucchini is of genetic origin. The presence of such plants is of concern.

In a separate incident 21 progeny from a bitter accession of C. pepo, 'Custard Squash' (origin unknown) was also evaluated. The progeny was considered as a F2 and plants segregated for fruit bitterness, 16 bitter to 5 non-bitter. However, bitterness of leaves segregated 5 bitter to 16 non-bitter and so there was a poor association of bitter leaves with bitter fruit. Plants which had bitter leaves also had bitter fruit but plants without bitter leaves sometimes had bitter fruit.

Literature Cited

  1. Andeweg, J. M. and J. W. de Bruyn. 1959. Breeding of non-bitter cucumbers. Euphytica 8:13–20.
  2. Robinson, R. W., H. M. Munger, T. W. Whitaker and G. W. Bohn. 1976. Genes of the cucurbitaceae. HortScience 12:554–568.

Market inspectors, extension officers and food technologists of the Queensland Department of Primary Industries, chemists of the Queensland Government Chemical Laboratory, inspectors of the Queensland, New South Wales and Victorian Health Departments and a plant breeder of the Department of Agriculture (Victoria) contributed information contained in this report.

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