A case for conserving plant pathogens

A case is made for the counter-intuitive proposal that plant pathologists and plant pathological societies should consider the development of policies for the conservation of plant pathogens. First the report of the Royal Botanic Gardens, Kew, entitled The State of the World's Plants and Fungi 2020, is reviewed briefly. Next, the reasons why plant pathologists should take this report seriously are outlined and the risks to plant pathogen diversity assessed. In this section and all that follow, the paper focuses on fungal (sensu lato) pathogens, although it is suggested that the general principles developed apply to most plant pathogens, whatever their taxonomic status. There then follows an assessment of native plant pathogens in the functioning, stability, and productivity of unmanaged and partially managed plant populations and communities. It is concluded that there is now compelling and growing evidence that very many do play a significant role. Also assessed, more briefly, is the actual or potential value of plant pathogens to human activities, such as selecting for novel disease-resistance factors in evolving populations of wild crop relatives, developing novel, sustainable plant disease and weed control strategies, use in industrial processes, and use as model systems for research. New and evolving genomics technologies are likely to facilitate significantly the study or selection of the benefits of plant pathogens to ecosystems or human activities. Potential strategies for the conservation of plant pathogens are outlined briefly, including in situ in unmanaged and partially managed ecosystems and centres of diversity of the progenitors of crop species, and ex situ in culture, spore, DNA, and herbarium collections. In these and many other areas of plant pathology, citizen science research groups have a potentially significant role. It is concluded that there is a strong case for plant pathologists and plant pathological societies to develop and act upon strategies for the conservation and sustainable use of plant pathogens.