652 ( I ) Direct effects of non-vector herbivores 653 (2) Indirect effects, mediated through the host 654 IV. Root-shoot interactions 657 ( I ) Above-ground insects and below-ground fungi 657 (2) Above-ground fungi and below-ground insects 658 . . . . . . 11. The effect of plant pathogenic fungi on herbivorous insects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (c) Effects on insects . . . . . . . . . . . . 648 . . . . . . 111. The effect of herbivorous insects on plant pathogenic fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V. Induced resistance a common defence against pest and pathogen ? . . . . 660 ( I ) The hypersensitive response and lignification . . . . . . . . 661 ( 2 ) Phytoalexins . . . . . . . . . . . . . . 662 (3) Proteinase inhibitors 663 (4) Lipoxygenase 664

Three‐way interactions between plant pathogenic fungi, herbivorous insects and their host plants

The impact of herbivory, fungi and competition on Mimosa pigra was studied in the field in Australia using insecticide and fungicide exclusion experiments and monitoring. The insect Neurostrota gunniella , a stem-boring moth imported for the biological control of M. pigra , had no apparent effect on seedling survival, which was, however, strongly reduced by inter- and intra-specific competition. In mature plants, the insect reduced radial growth of the canopy by about 14% in a season, but the insecticide had a negative effect on seed production, perhaps because it disrupted native pollinating insects. Fungicide had no effect, implying that native fungi were not affecting plant performance. A 5-year monitoring study showed a strong negative correlation between the density of the insect and seed output, such that seed output was 60% lower than normal at the highest densities of the insect. Furthermore, even at the lowest insect densities found in the field, the mean seed output and leaf litterfall were less...

Testing the Effects on Mimosa pigra of a Biological Control Agent Neurostrota gunniella (Lepidoptera: Gracillaridae), Plant Competition and Fungi Under Field Conditions

Dieback causes a progressive reduction in plant population health, resulting in the death of plant parts and often plant death. It is prevalent in many invasive woody weeds in Australia and has been suggested as a potential mechanism for biocontrol of these species. Parkinsonia aculeata one such invasive tree in northern Australia. It has naturalised across a wide range of climatic zones and some populations have been heavily reduced by dieback occurrence. The cause(s) of dieback in parkinsonia remain elusive, although fungal endophytes have been previously implicated. In this study, we characterised the culturable fungal endophyte community of healthy and dieback-affected parkinsonia using culture-based techniques, and identified cultured isolates via amplicon sequencing of the internal transcribed spacer (ITS) of the rDNA operon. Eight isolates, identified as pathogens, were selected for a 10-week pathogenicity trial, including water stress treatments, on parkinsonia seedlings. We isolated a taxonomically diverse fungal community from parkinsonia, representing 54 unique species from 25 families. Communities were similar across healthy and dieback-affected plants, but differed by plant tissue. Of the eight putative pathogenic isolates tested in the pathogenicity trial, inoculation with Lasiodiplodia pseudotheobromae, Botryosphaeria dothidea and Pestalotiopsis mangiferae resulted in the largest lesions, but systemic infection or dieback-like symptoms were not observed in any treatment despite plant stress being induced by drought or inundation. We concluded that inoculation of parkinsonia with the tested putative fungal pathogens is unlikely to result in dieback, which has implications for future work in biocontrol of parkinsonia.

Triggering dieback in an invasive plant: endophyte diversity and pathogenicity

Agents for biological control of Mimosa pigra in Australia: review and future prospects.

Background and aims Dieback is pervasive in many populations of invasive woody weeds globally. Previous studies on dieback have focused on specific potential causative biotic agents, but most cases remain unexplained. The potential role of endophytic microbial communities in dieback, including the relative importance of endophytes with pathogenic or protective capabilities, remains poorly studied. We tested whether changes in archaeal, bacterial and fungal endophyte community structure is associated with dieback occurrence in the invasive, leguminous tree, Parkinsonia aculeata L. (parkinsonia). Methods We sampled roots, stems and stem tips from healthyanddieback-affectedparkinsoniaandconducted terminal restriction fragment length polymorphism (TRFLP) analysis on DNA extracted from these samples using domain-specific primers for archaea, bacteria and higher fungi. Results Microbial community composition strongly differed with parkinsonia disease status (archaea, bacteria and fungi) and plant part (archaea and fungi). Plant part and disease status effects were strongest in archaea. We also found evidence implicating both pathogenic and potentially protective endophytes in the onset of dieback. Conclusions This is the first study that has shown significant associations between changes in endophyte community composition and dieback presence. Our results highlight the complexity of those changes and provide support for the hypothesis that diverse pathogenic and protective endophytes may be implicated in dieback.

Endophyte community composition is associated with dieback occurrence in an invasive tree

Widespread dieback of the introduced noxious weed Mimosa pigra was observed during the dry months in monsoonal northern Australia. Stems were girdled by reddish-brown lesions that generally originated from leaf axils. Botryodiplodia theobromae was consistently isolated from the lesions and was shown to cause the symptoms. It is suggested that the occurrence of dieback is linked with the establishment of a stem-boring moth introduced as a biological control agent for M. pigra.

C. G. Wilson

Papers

Botryodiplodia dieback of Mimosa pigra, a noxious weed in northern Australia