Oral Presentation Science Protecting Plant Health 2017

Investigating biofumigation and composted chicken manure to manage soilborne pathogens of avocado (4425)

Elizabeth K Dann 1 , Paulo S Souza 1 , Duy Le 1 , Louisa E Parkinson 1 , John D Duff 2
  1. Queensland Alliance for Agriculture and Food Innovation, University of Queensland, Dutton Park, QLD, Australia
  2. Department of Agriculture and Fisheries, Gatton Research Facility, Gatton, QLD, Australia

Avocado orchard productivity is reduced by soilborne pathogens, The principal one being root rot caused by Phytophthora cinnamomi, (Pc) and recently Dactylonectria macrodidyma (Dm) was also confirmed as a pathogen. Best management relies on implementation of several nursery and orchard practices, however, the efficacy of brassicaceous biofumigant plants to reduce soilborne disease has not been reported. In vitro Petri dish assays demonstrated that leaf extracts of Caliente (Brassica juncea) and BQ Mulch (B. napus + B. campestris) inhibited mycelial growth of Dm and Pc by 80-100%, at concentrations approximately equivalent to “field strength” (50 tonnes fresh weight/Ha). Nemat (Eruca sativa) inhibited growth of Dm and Pc by 66 and 36%, respectively.

An initial glasshouse study demonstrated that amendment of potting media with Caliente at concentrations approximately equivalent to 2x field strength (100 tonnes fresh weight/Ha) reduced root necrosis in avocado seedlings by nearly 40% five weeks after inoculation with Phytophthora cinnamomi, compared with plants that had been inoculated but received no amendment treatment. However, Caliente did not reduce root necrosis caused by Dm. Neither Nemat nor composted chicken manure reduced root necrosis caused by Pc or Dm. There were no significant differences among treatments for changes in seedling height or biomass of roots, leaves and stems. However, in the absence of pathogen, roots from the biofumigant treatments were more discoloured than those from the unamended control or chicken manure treatments. Further trials are necessary to evaluate whether biofumigation may have a role in the integrated management of avocado root rot diseases, in particular as a pre-plant treatment in orchards known to have a history of Pc and/or Dm infestation.