A case for re-inventory of Australia's plant pathogens

Abstract

Australia has efficient and visible plant quarantine measures, which through various border controls and survey activities attempt to prevent the entry of unwanted pests and diseases. The ability to successfully perform this task relies heavily on determining what pathogens are present and established in Australia as well as those pathogens that are exotic and threatening. There are detailed checklists and databases of fungal plant pathogens in Australia, compiled, in part, from surveys over many years sponsored by Federal and State programmes. These checklists and databases are mostly specimen-based, which enables validation of records with reference herbarium specimens and sometimes associated cultures. Most of the identifications have been based on morphological examination. The use of molecular methods, particularly the analysis of DNA sequence data, has recently shown that several well-known and important plant pathogenic species are actually complexes of cryptic species. We provide examples of this in the important plant pathogenic genera Botryosphaeria and its anamorphs, Colletotrichum, Fusarium, Phomopsis / Diaporthe and Mycosphaerella and its anamorphs. The discovery of these cryptic species indicates that many of the fungal names in checklists need scrutiny. It is difficult, and often impossible, to extract DNA for sequence analysis from herbarium specimens in order to validate identifications that may now be considered suspect. This validation can only be done if specimens are recollected, re-isolated and subjected to DNA analysis. Where possible, herbarium specimens as well as living cultures are needed to support records. Accurate knowledge of the plant pathogens within Australia’s borders is an essential prerequisite for the effective discharge of plant quarantine activities that will prevent or delay the arrival of unwanted plant pathogens.

Re-classification of the causal agent of white grain disorder on wheat as three separate species of Eutiarosporella

“…Hyde et al (2010) emphasised the need for up-to-date cataloguing of Australian fungal plant-pathogens (Hyde et al 2010). They illustrate this need by highlighting discrepancies between gene-sequence and morphological data attributed to a single Botryosphaeriaceae isolate (Hyde et al 2010 performing a Bre-inventory^of Australian fungal plantpathogens (Hyde et al 2010), as we too have highlighted nomenclature discrepancies that could only be resolved with genetic comparisons. To date, there are no published genetic studies analysing the maize pathogen, B. zeae, although morphologically they are believed to be similar to wheat-infecting Eutiarosporella spp.…”

“…Modern genetic data is vital for continued examination and differentiation of fungal pathogens (Hyde et al 2010). Currently, there are no sequenced genes of B. zeae present on GenBank or similar publicly available gene databases.…”

The need to carry out re-inventory of plant pathogenic fungi

“…In a recent paper Hyde et al (2010) were of the opinion that plant pathologists and mycologists should re-inventory Australian plant pathogens in order to make quarantine measures more effective. The purpose of this paper is to give examples of some selected tropical plant pathogenic genera where the utilization of updated species concept and species recognition criteria (Cai et al, 2011) has improved the discrimination for delimiting species.…”

Cryptic Species: A Leitmotif of Contemporary Mycology Has Challenges and Benefits for Plant Pathologists

“…Fusarium verticillioides causes stalk rot of maize (Zea mays) and produces fumonisin, whereas F. thapsinum causes stalk rot of sorghum (Sorghum bicolor) and does not produce fumonisin. Fusarium andiyazi can also cause some disease in sorghum (Hyde et al 2010). Host preference and mycotoxin production are strong considerations in management of Fusarium-induced diseases of cereals and other crops.…”

“…), and F. mangiferei (causing a deformation in mango, Mangifera indica). The latter two are of quarantine importance in Australia (Hyde et al 2010). …”