Nipponaclerda biwakoensis infestation of Phragmites australis in the Mississippi River Delta, USA: Do fungal microbiomes play a role?

Recently, significant die-back of nonnative common reed, Phragmites australis, has been reported in the Mississippi River Delta (MRD), Louisiana, USA. This dieback has been attributed to an invasive scale insect, Nipponaclerda biwakoensis. We test whether fungi are involved in the recent infestation by this insect and subsequent die-offs of Phragmites australis. Several haplotypes of P. australis occur in the MRD, and the European (M) and Delta (M1) haplotypes appear to experience differing levels of N. biwakoensis infestation. We tested whether these haplotypes differed in their fungal microbiomes in both their leaf and stem tissues, and whether differences in fungal community composition were linked to the level of infestation using a metabarcoding Internal Transcribed Spacer (ITS) amplicon sequencing approach. Our analyses showed differences in fungal community composition and diversity between haplotypes and tissue types, but none of these differences were directly correlated with N. biwakoensis infestation severity. However, we did find that the European haplotype hosted higher putative pathogen loads in stem tissues compared to the Delta haplotype, which may confer resistance to herbivory, though it is possible that differences in infestation between haplotypes are due to morphology.