Plant ‘dieback’ is loosely defined by overall health decline, leaf and stem death and eventually whole plant mortality. Dieback significantly reduces populations of multiple cultivated, desired and invasive plant species globally. Early diagnosis of dieback is difficult because it can potentially be due to a complex interaction of factors including environmental conditions, pathogen community composition and plant-microbe interactions.
In instances where there is a single putative pathogen causing plant death, it is possible to verify its causal role through testing Koch’s postulates. However many examples of dieback in plants are associated with the hosts’ community of fungal endophytes. This has been shown for trees such as native jarrah, weeds including Parkinsonia aculeata, and grasses such as Sporobolus sp. Although dieback has been studied in multiple systems, past understanding of this phenomenon has traditionally focused on the use of culture-based techniques alone. Since endophyte communities themselves are complex and consist of hundreds of taxa, testing Koch’s postulates in such contexts is difficult.
Here I outline a potential approach for investigating dieback phenomena where multiple causal agents may be involved and where diagnosing which endophytes might be pathogenic or dieback-inducing is difficult. This framework requires a sequence of methodologies beginning with traditional culture-based fungal isolations and ID, followed by next-generation sequencing of the fungal endophyte community, statistical analysis of community composition in relation to dieback occurrence and identification of pathogenic taxa likely to be involved in dieback. Subsequently, isolation strategies are designed for any remaining putative pathogens, and then pathogenicity screening is conducted in the context of environmental variables.
Adopting this approach for dieback research in forestry, environmental and agricultural systems can lead to better diagnoses of causes of plant death. This would have significant implications for enhancing the productivity of desirable plant species and suppressing populations of invasive plant species.