Student Project: Horticultural protocols for experimental studies of eyebrights (Euphrasia, Orobanchaceae)

Parasitic plants are particularly challenging to cultivate as the growth conditions must be suitable for the parasite, the host, and their interaction. Here, we review our progress growing British native eyebrights (Euphrasia), a group of hemiparasitic plants found in diverse habitats in Britain and Ireland. We consider the protocols required to grow them under a range of conditions, including the laboratory, in pot trials, in cultivated fields, and in the wild. We highlight the need to use seed stratification to break seed dormancy, to replicate planting to overcome low seed viability, and to manage host plants to avoid competition. While Euphrasia can be successfully grown in different environments more work is required to develop reliable horticultural protocols for growing plants under natural conditions.

Performance of generalist hemiparasitic Euphrasia across a phylogenetically diverse host spectrum

Generalist hemiparasites may attach to many different host species and experience complex parasite-host interactions. How these parasite-host interactions impact on the fitness of hemiparasitic plants remain largely unknown. We used experimentally tractable eyebrights (Euphrasia, Orobanchaceae) to understand parasite-host interactions affecting the performance of a generalist hemiparasitic plant. Common garden experiments were carried out measuring Euphrasia performance across 45 diverse hosts and in different parasite-host combinations. We showed that variation in hemiparasite performance could be attributed mainly to host species and host phylogenetic relationships (λ = 0.82; 0.17–1.00 CI). When this variation in performance is broken down temporally, annual host species cause earlier flowering, and lead to poorer performance late in the season. While Euphrasia species typically perform similarly on a given host species, some eyebrights show more specialised parasite-host interactions. Our results show that generalist hemiparasites only benefit from attaching to a limited, but phylogenetically divergent, subset of hosts. The conserved responses of divergent Euphrasia species suggest hemiparasite performance is affected by common host attributes. However, evidence for more complex parasite-host interactions show that a generalist hemiparasite can potentially respond to individual host selection pressures and may adapt to local host communities.

In vitro tissue culture, preliminar phytochemical analysis, and antibacterial activity of Psittacanthus linearis (Killip) J.K. Macbride (Loranthaceae)

Hemiparasitic plants commonly known as mistletoe (muérdago in Spanish) in the families Santalaceae and Loranthaceae are common in various kinds of plants or trees, and many hemiparasitic plants are used for medicinal purposes in various parts of the world. The objective of the present work, carried out in Psittacanthus linearis (suelda con suelda), a representative species in the seasonally dry forest (SDF) from the north of Perú, was to study aspects of in vitro tissue culture, carry out preliminary phytochemical analysis, and assess antibacterial activity. Seeds of individuals of P. linearis, which used Prosopis pallida (algarrobo) as host plant, were collected and used to induce in vitro seed germination, clonal propagation, callus induction and organogenesis. Stems, leaves and fruits of individuals of P. linearis were dried, powdered, and subjected to ethanol extraction. Posteriorly the extract was first recovered with ethanol and the remnant with chloroform, which formed the ethanolic and chloroformic fraction. A preliminary phytochemical screening was performed and preliminary antibacterial studies with Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were carried out and their results are discussed. This is the first report about in vitro tissue culture, phytochemical analysis and antibacterial activity of P. linearis. The results may have important implications for understanding physiological and biochemical interactions between host and hemiparasitic species as well as P. linearis with P. pallida and other SDF species.

Hemiparasitic interaction between Castilleja tenuiflora (Orobanchaceae) and Baccharis conferta (Asteraceae): haustorium anatomy and C- and N-fluxes

<p><strong>Background:</strong><em> Castilleja tenuiflora</em> is a hemiparasite of <em>Baccharis conferta</em>. The haustorium is the characteristic structure of hemiparasitic plants and its anatomy varies depending several factors such as host species, position on the root and environment.</p><p><strong>Question: </strong>What is the structure and anatomy of haustoria builded in field interaction? Based on C, N and chlorophyll contents, is <em>C. tenuiflora</em> a facultative hemiparasite of <em>B. conferta</em>?<strong></strong></p><p><strong>Species studied: </strong><em>Castilleja tenuiflora</em> Benth. and <em>Baccharis conferta</em> Kunth.<strong></strong></p><p><strong>Study site and dates:</strong> Plant materials were collected in the Iztaccihuatl-Popocatepetl National Park (N 19° 0.5´ 9.6'', W 98° 40´ 24.2'', 3,480 m.a.s.l.), State of Mexico, Mexico, in December 2013.<strong></strong></p><p><strong>Methods</strong>: Individuals of <em>B. conferta</em> and <em>C. tenuiflora </em>growing independently or in hemiparasite interactions were collected and samples were processed for anatomical and histochemical characterization, determination of C, N and chlorophyll.</p><p><strong>Results:</strong><em> </em>Haustoria were globular and located mainly in the lateral roots of <em>B. conferta</em>. Anatomy of haustorium shows the characteristic structures: exophyte and endophyte. Haustorial tissues storage starch, tannins and essential oils while in the <em>B. conferta</em> roots also calcium oxalate crystals were found. C levels were significantly influenced by hemiparasitic interaction. This is the first study that characterizes a hemiparasitic interaction in the field and specifically between <em>C. tenuiflora</em> and <em>B. conferta</em>.</p><strong>Conclusions:</strong><em> </em>Haustoria builded in interaction with <em>B. conferta</em> show the characteristic structure and anatomy. Hemiparasitic relationship represents for <em>C. tenuiflora</em> a source of C and other compounds such as essential oils.