Response of Roseau Cane (Phragmites australis) to Two Biotic Stresses: Hyalopterus pruni and Bipolaris yamadae

Roseau cane (Phragmites australis) is considered an invasive plant because of its ability to replace native plant species. However, in Louisiana it plays an important role protecting coastal infrastructure and being part of the marsh ecosystem in the lower Mississippi River Delta. In recent years, Roseau cane has been affected by a die-off, a problem that has also been reported in some European countries. Possible biotic and abiotic factors that have been associated with the die-off include scale insects, climate change, pollution, salinity levels, and pathogens. In this research, the individual and combined effect of a foliar disease and an insect herbivore on Roseau cane was investigated on two different lineages of Roseau cane (Delta and European). A foliar disease caused by the fungus Bipolaris yamadae and the feeding damage caused by the mealy plum aphid (Hyalopterus pruni) were evaluated. A colony of aphids used in feeding experiments was established and the aphid’s species identified. Fungal inoculations using spore suspensions from cultures of B. yamadae and insect infestations were conducted. At the end of the aphid feeding experiments, the number of mealy plum aphids was higher on the Delta lineage than the European lineage. Moreover, the Delta lineage had higher aphid damage ratings than the European lineage. The heights of plants with aphids were not statistically significantly different from the heights of plants without aphids. This was also true for the heights of the plants simultaneously infected and infested with B. yamadae and H. pruni respectively. In inoculation experiments with B. yamadae alone, the number of leaf lesions on the Delta lineage was statistically significantly higher than the number of leaf lesions on the European lineage. In contrast, in experiments when the mealy plum aphids were also included, the number of leaf lesions caused by B. yamadae was not statistically different. Both, the mealy plum aphid, and B. yamadae were able to reproduce simultaneously on Roseau cane and caused foliar symptoms; however, their interactions appear to be limited