Selection for decreased sensitivity to phosphite in Phytophthora cinnamomi with prolonged use of fungicide

• Published in: Plant pathology Vol. 57; no. 5; pp. 928 - 936
• Main Authors: Dobrowolski, M.P, Shearer, B.L, Colquhoun, I.J, O'Brien, P.A, Hardy, G.E. StJ
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.10.2008; Blackwell Publishing Ltd; Blackwell
• Subjects: avocados; Biological and medical sciences; Eucalyptus sieberi; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; fungicide resistance; Oomycetes; Persea americana; phosphonate; Phytopathology. Animal pests. Plant and forest protection; Phytophthora cinnamomi; selection; Plant pathology; Plant pathogen; Selection; oomycetes; phosphonate; Persea americana; Climacteric; Inorganic compound; Tropical fruit; Phosphites; Phytophthora cinnamomi; Dicotyledones; Angiospermae; Fruit tree; Pesticide resistance; Lauraceae; Stramenopila; Use; Pesticides; fungicide resistance; Inorganic ion; avocados; Oomycota; Mineral matter; Fungicide; Inorganic anion; Sensitivity resistance; Fruit crop; Avocado; Phosphorus compound; Spermatophyta
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1111/j.1365-3059.2008.01883.x

To test the hypothesis that resistance in Phytophthora cinnamomi to control by the fungicide phosphite (phosphonate) would arise in sites with prolonged use of phosphite, 30 P. cinnamomi isolates were collected from a range of sites with different phosphite-use histories, including phosphite-treated and untreated avocado orchards, and phosphite-treated and untreated native vegetation sites. The colonizing ability of these isolates was tested by different inoculation methods against a range of host tissues, treated and untreated with phosphite, including mycelial stem inoculation on clonally propagated Leucadendron sp., mycelial root inoculation of lupin seedlings and zoospore inoculation of Eucalyptus sieberi cotyledons. Isolates from avocado orchards with a long history of phosphite use were, on average, more extensive colonizers of the phosphite-treated Leucadendron sp., lupin seedling roots and Eucalyptus sieberi cotyledons. These isolates did not colonize untreated plant tissue (Leucadendron sp.) more extensively than isolates from sites with no history of phosphite use and no isolates were resistant to control by phosphite. Analysis of all isolates with microsatellite markers revealed the majority were from a single clonal lineage. Selection for decreased sensitivity to phosphite in planta has taken place within asexual clonal lineages of P. cinnamomi in sites with prolonged use of phosphite.