Tomato: Microorganisms in the irrigation water of hydroponic crops grown in closed systems

Project summary:

In glasshouse grown tomato there has been a marked shift towards re-circulation of nutrient solution in ‘closed irrigation systems’ which reduce water and nutrient use and the risk of environmental pollution.  However, where nutrient solution is recycled there is an increased risk of serious root disease problems. Pathogens shown to be transmitted in nutrient solution and which can cause serious disease in tomato include Pythium aphanidermatum, Phytophthora nicotianae, Fusarium oxysporum f. sp. radicis-lycopersici and PepMV.  Work in PC 281a detected consistent occurrence of several root-infecting plant pathogens including Colletotrichum coccodes, Fusarium oxysporum, Pythium spp. and Verticillium albo-atrum in three hydroponic crops monitored throughout 2013.  All three crops were grown on Maxifort rootstock and none developed serious root disease.  PC 281a found that a relatively stable microbial population was present on roots from planting, and that the microbial diversity on roots was greater in closed systems than run-to-waste crops.  Work was restricted to three crops, one rootstock and one season, so it is unclear if lack of root disease was due to rootstock vigour, microbial diversity or a hitherto unknown reason.  The aim of the current work is to increase knowledge on occurrence of microorganisms in irrigation water where nutrient solution is recycled to better understand the risks of root disease and provide greater confidence as growers move to these systems.  Specifically, the project aims to: 1) identify microorganisms present at different positions in the closed water system of hydroponic tomato crops; 2) compare the microbial populations before and after different water disinfection treatments; 3) compare the susceptibility of own-root and grafted tomato plants to four fungal and oomycete pathogens commonly found in hydroponic solution; 4) determine occurrence of root disease and root microbial populations in 10 tomato crops grown in closed systems with re-circulation; 5) Communicate results to growers.  The project will use as a basis the techniques and methods developed in PC 281a and be delivered jointly by the University of Nottingham (dedicated MRes student) and ADAS.

Benefits to industry:

• Targeted diagnostics for use by researchers to study tomato root microorganisms.
• Knowledge of the distribution of potential pathogenic and beneficial microorganisms in the water ‘closed loop’ when crops are grown with re-circulation; how best to maintain beneficial populations.
• Insight into the effect of different water disinfection treatment systems on key plant pathogens and beneficial microorganisms in irrigation water.
• Evaluation of relative susceptibility of own-root and grafted plants to four root-infecting pathogens.
• Improved understanding of the risk of root disease in grafted crops grown with re-circulation and at different inoculum levels of common pathogens.
• Increased confidence for growers to grow crops in closed systems with re-circulation.
• Potential to extrapolate findings from closed hydroponic production systems and apply to and further develop for organic soil-grown crops.

Aims and objectives:

Project aim(s):

 To characterise and quantify microorganism populations in irrigation water and assess the risk of root disease when tomato crops are grown in closed irrigation systems with recirculation of the nutrient solution

Project objective(s):

 To further validate the microarray previously used for monitoring tomato rhizosphere microorganisms, and to integrate this with specific quantitative PCR based diagnostics for four specified tomato root pathogens.

1. To determine the effect of water disinfection treatment, sampling location and crop age on the occurrence of microorganisms in water in tomato crops grown in closed systems with recycled nutrient solution.
2. To compare the pathogenicity of four fungal and oomycete root pathogens commonly found in hydroponic crops to own-root and grafted plants of tomato.
3. To monitor 10 commercial crops grown in closed systems with recycled irrigation solution for root pathogens and root disease.
4. To communicate results to tomato growers and the wider horticulture industry.