Root diseases pose a serious threat to tomato production, with an increased risk where irrigation run-off is recycled. There is increasing evidence that a wide diversity of microbes on roots can benefit plant health by reducing opportunities for root pathogens to take hold, and inducing systemic resistance to some foliar diseases.
AHDB Horticulture has funded a series of projects in this area. Project PC 281 used molecular diagnostics to reveal the diversity of micro-organisms on tomato roots. This was followed by PC 281a, which improved the ability to detect tomato root pathogens and our understanding of the interactions between them and the beneficial microbes around the roots.
The overall objective of the latest project, PC 281b, was to utilise the tomato root microarray developed in PC 281a, in combination with specific quantitative diagnostic techniques (multiplex qPCR) for four key tomato root pathogens, to characterise and quantify micro-organism populations in irrigation water. This would then allow assessment of the risk of root disease when tomato crops are grown in closed irrigation systems with recirculation of the nutrient solution.
From studying 10 crops grown in recirculated solution through 2015, it was shown that the overall micro-organism species richness increased in irrigation water as crops aged, and the abundance of common tomato pathogens increased. Low levels of root disease were observed in the crops monitored, but associations between observable root issues and low species richness and diversity were observed.
The final reports for all projects mentioned are available on the AHDB Horticulture website (horticulture.ahdb.org.uk).