First Report of Dodder (Cuscuta epithymum) Parasitizing Hemiparasitic Species of Santalaceae (Thesium) and Orobanchaceae (Euphrasia, Melampyrum, Odontites, Orthantha, and Rhinanthus) in Poland

Abstract

Cuscuta epithymum L. (Convolvulaceae) is native to Europe, western Asia, and northern Africa but occurs worldwide and infects many crops, especially legumes, as well as wild plants. Epiparasites (also called hyperparasites) are parasitic plants that parasitize other parasitic plants of a different species. Epiparasitism in world flora is known only within Viscaceae and rarely in Santalaceae and Eremolepidaceae (Calvin and Wilson 2009). Field surveys conducted in southern Poland in May to September 2015 and 2016 revealed parasitic attachment of the holoparasitic Cuscuta epithymum on the shoots of several hemiparasitic species: Thesium linophyllon (Santalaceae) and Odontites serotina, Orthantha lutea, Melampyrum arvense, Euphrasia stricta, and Rhinanthus glaber (Orobanchaceae). These occurred in four localities located in the Nida Basin (Malopolska Upland): Kikow, Sedziejowice, Skowronno, and Samostrzalow, in xerothermic grasslands, old quarries, and on the edges of cultivated fields in Solec-Zdroj (50°22′05″N, 20°51′27″E), Chmielnik (50°34′21″N, 20°39′45″E), Pinczow (50°32′21″N, 20°30′34″E), and Kije (50°35′29″N, 20°38′32″E) counties (altitude: 250 to 287 m above sea level). The surveyed area covered about 600 m², and the epiparasitic incidence was 30 to 50% total parasitism of all hemiparasitic species. The dodder population covered 20 to 80% of shoots of these hemiparasitic species, especially T. linophyllon. The host plants parasitized by the dodder showed poor growth, and their leaves became chlorotic. The epiparasites spread aggressively in the primary tissues of the host, particularly in its stems and leaves, as well as inflorescences. The main botanical features of the dodder were as follows: (i) stem 0.2 to 0.4 mm, thready, reddish to purplish, rootless, leafless, with short haustoria; (ii) inflorescence compact, spherical, ∼20 flowered; (iii) flowers sessile, white, pink to purplish, 2 to 3 mm long, with five sepals and petals; and (iv) fruits, globose capsule with usually four small seeds, ∼1 mm. For phylogenetic study the total genomic DNA was extracted, and the internal transcribed spacer (ITS) region was amplified and sequenced using the ITS7A (Aguilar et al. 1999) and ITS4 (White et al. 1990) primers. The obtained 624-bp long ITS region sequence was deposited in GenBank (accession no. KY707298). The sequence showed the highest similarity (99%) to sequences of C. epithymum (DQ924606, DQ924605, and DQ924609). To our knowledge, this is the first report of holoparasitic C. epithymum as an epiparasite on hemiparasitic species of Santalaceae and Orobanchaceae, and simultaneously the first report of epiparasitism in Convolvulaceae, representing a unique phenomenon in epiparasitism worldwide. C. epithymum, if left unabated, affects yield or influences chemical composition of infected host-parasites used therapeutically, because of dodder toxicity aspect, and thereby the medical properties of any commercial-scale production hemiparasites (especially the widely used herb Euphrasia) in the future. Epiparasitism could limit the negative effect of the parasite on the primary host (Kuijt and Lye 2005). The epiparasite may harm the host parasite relatively more than the same parasite would harm a nonparasitic host (Heide-Jorgensen 2008).