Abstract
Understanding changes in the interactions between parasitic plants and their hosts in relation to ontogenetic changes in the hosts is crucial for successful use of parasitic plants as biological controls. We investigated growth, photosynthesis and chemical defences in different-aged Bidens pilosa plants in response to infection by Cuscuta australis. We were particularly interested in whether plant responses to parasite infection change with changes in the host plant age. Compared with the non-infected B. pilosa, parasite infection reduced total host biomass and net photosynthetic rates, but these deleterious effects decreased with increasing host age. Parasite infection reduced the concentrations of total phenolics, total flavonoids and saponins in the younger B. pilosa but not in the older B. pilosa. Compared with the relatively older and larger plants, younger and smaller plants suffered from more severe damage and are likely less to recover from the infection, suggesting that C. australis is only a viable biocontrol agent for younger B. pilosa plants.
Highlights
A parasitic plant is a type of angiosperm that directly attaches to another plant via a haustorium (Press 1998)
We aimed to answer the following questions: (i) Do younger and older B. pilosa plants differ in their responses to infection by C. australis? (ii) Are these differences in responses are correlated with the growth of different-aged invasive host plants? The answers to these questions could provide basic scientific knowledge for using C. australis to manage the invasive plant B. pilosa
Cuscuta australis infection decreased the root, stem, leaf and total biomass of the hosts compared with the controls within each age class (Fig. 1, upper panel), and this negative effect on host growth significantly decreased with increasing host age (Fig. 1, lower panel)
Summary
A parasitic plant is a type of angiosperm (flowering plant) that directly attaches to another plant via a haustorium (Press 1998). Over 4500 known plant species are parasitic to some extent and acquire some or all of their water, carbon and nutrients from a host (Press 1998; Li et al 2014). Infection by parasitic plants has been considered as an effective method for controlling invasive plants because the parasites partially (hemiparasites) or completely (holoparasites) absorb water, nutrients and carbohydrates from their host plants, suppressing the vitality of the host (Parker et al 2006; Yu et al 2008, 2009; Li et al 2012). Compared with the effects of feeding by herbivores, the defence responses of plants infected by parasitic plants have rarely been studied (Runyon et al 2006; Ranjan et al 2014), even though such knowledge is important for the successful use of parasitic plants as enemies against invasive plants
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