On 29 May 2013, Stefanie Pflug presented the results of her research conducted at Wageningen University, the Netherlands. In her experiments she studied the interaction between the parasitic weed Rhamphicarpa fistulosa and its host rice (Oryza sativa).
The research focussed on two aspects of the host-parasite interaction: 1) The influence of host plant size, developmental stage and parasite size on growth of both rice and parasitic weed, and 2) The effect of the parasite on host photosynthesis.
In order to address these objectives, Stefanie conducted a greenhouse experiment in which she planted rice and R. fistulosa both in associations and as monocultures (controls). To create rice plants of two different sizes, rice seeds were sown at two different points in time and R. fistulosa seeds were added at one point in time. Growth of host plant and parasitic weed as well as host photosynthesis was observed for six dates, starting four weeks after the sowing of the parasite seeds.
The study has shown that:
1) An increased growth of R. fistulosa compared to their controls was observed earlier for the R. fistulosa plants growing with the older and therefore larger rice plants. At a later stage, these R. fistulosa plants had no growth advantage over the R. fistulosa plants that had attached slightly later to the younger rice plants. The growth of the attached parasitic weed was therefore not dependent on the size of the host plant. Compared to the controls, with R. fistulosa-infected rice plants showed a reduced growth. A shift in dry matter allocation towards the roots was observed as root dry weights did not differ between uninfected and infected rice plants, whereas shoot dry weights were strongly reduced in infected rice plants. Furthermore, plant height and leaf area was reduced in infected rice plants.
2) At the leaf level, infected rice plants showed a reduced level of leaf greenness and a reduced maximum photosynthetic rate. It was also observed that reductions in host biomass production occurred prior to reductions in maximum photosynthetic rate. Additionally, rice plants that were smaller at infection were stronger affected than the larger rice plants.