Ex Situ Propagation of Philippine Rafflesia in the United States: Challenges and Prospects

Abstract

The large-flowered parasitic genus Rafflesia R.Br. (Rafflesiaceae) has long fascinated naturalists and scientists and is an iconic symbol for plant conservation. Techniques to effectively propagate members of the genus outside of their natural habitat are sparse, and grafting infected Tetrastigma K.Schum.(Vitaceae) host plants has previously been reported as a successful strategy for ex situ conservation of Rafflesia. Here we report our attempts in the United States to propagate host cuttings infected with Rafflesia speciosa Barcelona & Fernando and R. lagascae Blanco collectedfrom the Philippines, as well as uninfected host material. We also describe efforts to germinate R. speciosa seeds in vitro using various plant growth regulators (PGRs). After rooting, infected host cuttings survived for a maximum of 11 months, but did not produce shoots. However, an uninfected cutting of T. cf. magnum grafted onto an established Malaysian species of Tetrastigma in June 2017 has succeeded in the commencement of new growth. Three propagules of a second potential host, T. harmandii Planch., have also been vigorously growing at the United States Botanic Garden since June 2017. However, Rafflesia seeds did not germinate with the application of PGRs, even though the seeds were viable according to tetrazolium (TZ) testing.These ex situ propagation attempts have revealed challenges in propagating these species outside of their native ranges, but our incremental success in rooting infected Tetrastigma, as well as grafting interspecific Tetrastigma species, bodes well for further advances. With Philippine host species, T. harmandii and T. cf. magnum in cultivation, we can begin using these specimens for future experimentation involving grafting of infected material and Rafflesia seed inoculation trials.Furthermore, we describe new avenues of propagation techniques for Rafflesia as practised by Marius Gabin, one of the owners of the Vivian Rafflesia garden, which contains a natural Rafflesia forest habitat at Poring Springs, Sabah, Malaysia. Gabin openly shared his successes in artificially inoculating Rafflesia seeds into a mature Tetrastigma vine. Gabin’s willingness to share his experience highlights the importance of collaborating with practitioners who have developed local knowledge of Rafflesia horticulture and conservation.

Striking developmental convergence in angiosperm endoparasites

“…5A). Nevertheless, germination assays conducted for Apodanthaceae and Rafflesiaceae species in which parasite seeds have been placed in close contact or even within host tissues have been unsuccessful (Brasil, 2010; Molina et al, 2017). These negative results suggest that these endoparasites might depend on specific host‐derived signals for germination, as reported for several other parasitic plants, especially those that lack photosynthetic activity (Baskin and Baskin, 2014).…”

Endoparasitic plants and fungi show evolutionary convergence across phylogenetic divisions

“…Note that the diagrammatic representation in Fig. 2 germinate the seeds of endoparasitic plants artificially using approaches successful in other parasitic plants have failed, for example the use of plant growth regulators (Molina et al, 2017). The scant available reports of artificial germination of Rafflesiaceae seed have been summarized by Wicaksono et al (2020), highlighting that successful attempts involve spreading and, or rubbing parasite seeds upon the stems of suitable hosts.…”

“…Note that the diagrammatic representation in Fig. 2 germinate the seeds of endoparasitic plants artificially using approaches successful in other parasitic plants have failed, for example, the use of plant growth regulators (Molina et al, 2017).…”

Rhizanthes, the Forgotten Relative of Rafflesia in the Rafflesiaceae

“…There is very little research on the propagation (in vivo and in vitro seed germination, and tissue culture) of Rhizanthes, so cues could be taken from more extensive studies on Rafflesia, including host grafting (Mursidawati et al, 2015), seed germination (in vivoboth in situ and ex situand in vitro; Mursidawati al., 2015;Molina et al, 2017;Wicaksono et al, 2016), and tissue culture (Sukamto, 2001;Mursidawati & Handini, 2009;Sukamto & Mujiono, 2010;Wicaksono & Teixeira da Silva, 2015).…”