Cause Cucurbitacins, which are a group of plant-produced, bitter chemical compounds that occur naturally in this plant family. These compounds occur in a subset of the species in cucurbit plant family and are usually found at highest concentrations in the roots of plants. Over the years that humans have been developing cucurbit varieties, cucumbers, melons, squash and pumpkins lines have been selected to be free of of high levels of these extremely bitter compounds. Modern-day varieties of zucchini and other cucurbits should generally be free of cucurbitacin in fruit, but seed lines produced from plants that have been inadvertently pollinated by cucurbits that still produce higher levels of cucurbitacins, can result in plants that can yield fruit with higher levels of these bitter compounds. The occurrence of cucurbitacins was detected in canned zucchini and other squashes, suggesting that at least some forms of cucurbitacin are heat stable. Cucurbitacins can be toxic to domesticated animals and humans if consumed in high enough quantities. Abiotic or biotic stresses, including water stress, may result in higher levels of cucurbitacins in cucurbit fruit. High levels of nitrogen may also facilitate the accumulation of higher levels of cucurbitacins in fruit.
Symptoms Fruit that contain greater levels of cucurbitacins appear normal, however, the fruit will have a bitterness to their flavor. However, the bitterness may be masked, depending on how the squash are prepared and accompanying spices/flavorings. When animals consume cucurbit fruit containing cucurbitacins and receive a high enough dose, the intestines and other organs are affected. Individuals that consume intoxicating levels of cucurbitacins will undergo an irritation of the intestines and experience greatly increased intestional motility. The lungs, pancreas, liver, and kidney can also be affected, along with a reduction in the red blood cells levels. The reported cases of human poisonings are relatively small, so information on the affects in humans is limited. Generally humans will experience drooling and vomiting within minutes of consuming high levels of cucurbitacins. Humans in the US exposed to small amounts of zucchini containing cucurbitacins (0.1 ounce of zucchini) experienced an irritation of their intestines, greatly increased intestional motility (diarrhea), headaches, severe stomach cramps, and collapsed within 1 to 2 hours of ingesting the intoxicating summer squash.
Cultural control
- Do not eat squash or other cucurbit fruit if there is a noticeable bitterness.
- Obtain cucurbit seed from reputable sources.
- Avoid planting seeds that were harvested from cucurbits produced in home gardens where outcrossing could have occurred with cucurbit plants that contain cucurbitacins.
- Provide adequate water to plants so that drought stress is avoided.
- Use a good fertility program that provides adequate nitrogen but avoid over-application of nitrogen that could enhance build up of cucurbitacins in squash fruit.
References Gry, J., Søborg, I., and Christer Andersson, H. 2006. Cucurbitacins in Plant Food. https://doi.org/10.6027/TN2006-556. On-line at https://www.diva-portal.org/smash/get/diva2:701868/FULLTEXT01.pdf
Mashilo, J., Odindo, A.O., Shimelis, H.A., Musenge, P., Tesfay, S.Z., and Magwaza, L.S. 2018. Photosynthetic response of bottle gourd [Lagenaria siceraria (Molina) Standl.] to drought stress: Relationship between cucurbitacins accumulation and drought tolerance. Scientia
Horticulturae 231:133-143.
Rymal, K.S., Chambliss, O.L., Bond, M.D., Smith, D.A. 1984. Squash containing toxic cucurbitacin compounds occurring in California and Alabama. J. Food Prot. 47(4):270-271.