Chapter 14: Plant Pathogens and Control Strategies in Aquaponics

Among the diversity of plant diseases occurring in aquaponics, soil-borne
pathogens, such as Fusarium spp., Phytophthora spp. and Pythium spp., are the most
problematic due to their preference for humid/aquatic environment conditions.
Phytophthora spp. and Pythium spp. which belong to the Oomycetes pseudo-fungi
require special attention because of their mobile form of dispersion, the so-called
zoospores that can move freely and actively in liquid water. In coupled aquaponics,
curative methods are still limited because of the possible toxicity of pesticides and
chemical agents for fish and beneficial bacteria (e.g. nitrifying bacteria of the
biofilter). Furthermore, the development of biocontrol agents for aquaponic use is
still at its beginning. Consequently, ways to control the initial infection and the
progression of a disease are mainly based on preventive actions and water physical
treatments. However, suppressive action (suppression) could happen in aquaponic
environment considering recent papers and the suppressive activity already
highlighted in hydroponics. In addition, aquaponic water contains organic matter
that could promote establishment and growth of heterotrophic bacteria in the system
or even improve plant growth and viability directly. With regards to organic
hydroponics (i.e. use of organic fertilisation and organic plant media), these bacteria
could act as antagonist agents or as plant defence elicitors to protect plants from
diseases. In the future, research on the disease suppressive ability of the aquaponic
biotope must be increased, as well as isolation, characterisation and formulation of
microbial plant pathogen antagonists. Finally, a good knowledge in the rapid
identification of pathogens, combined with control methods and diseases monitoring,
as recommended in integrated plant pest management, is the key to an efficient
control of plant diseases in aquaponics.