An introduced plant in Ireland, Black Nightshade (Solanum nigrum) is a annual that grows in waste places, roadsides and often as a garden weed (Phillips, 1977 Wild Flowers of Britain p. 116). It has small flowers with white, united petals and yellow anthers that ripen to black berries. The broad, ovate leaves are born on stems that are angular, erect and broadly branched (Toušová, 1978, Wildflowers of Field and Woodland pp. 74-75). The berries are poisonous, containing alkaloids such as solasodine, solasonine and solanidine, (Perez et al., 1998 Journal of Ethnopharmacology 62 pp. 43-48) and are toxic if consumed.
This cocktail of chemicals has lead to extensive research on the pharmacological activity of S. nigrum. Extracts from the fruit and dried plants have been shown to have hepatoprotective and antiulcerogenic effects: plant extracts are effective against liver fibrosis in mice (Hsieh, 2008 Journal of Ethnopharmacology 119 pp. 117-121) and fruit extracts inhibit gastric lesions in rats, as well as controlling gastric secretory volume, acidity and pepsin secretion (Jainu and Devi, 2006 Journal of Ethnopharmacology 104 pp. 156-163).
However as a member of the same family as potato (Solanaceae), S. nigrum has been shown to act as an alternative host for the late potato blight, Phytophthora infestans. Late blight is estimated to cause €10.2 million worth of losses per annum in Ireland (Copeland et al., 1993. Vulnerability of the Irish potato industry to harmful organisms pp. 95-106). The parasitic fungus infects the leaves of the plant, causing necrosis by its feeding action which leads to the characteristic black lesions associated with blight. Following an outbreak of the disease, the rate of development of an epidemic is weather dependent and in Ireland such epidemic proportions are thought to be reached in 7 out of 10 years (Dowley et al., 2008 Irish Journal of Agricultural and Food Research 47 pp. 69–78). Flier et al. (2003, Plant Pathology 52 pp. 595–603) have shown that S. nigrum is readily infected with late blight and infected plants generate a considerable source of infection, suggesting it could be a significant disease reservoir.