Ramularia leaf spot management alternatives in barley optimizing the use of fungicides for its control

Doctoral thesis abstract

Abstract

Ramularia collo-cygni (Rcc) is the causal agent of Ramularia leaf spot (RLS). The main management tool is the use of foliar fungicides, the impact of which on cereal safety is unknown. Therefore, the aim of this thesis was to optimise the management of ramulariosis in barley and to minimise fungicide residues in grain. The specific objectives were: (i) to validate a method for the detection and quantification of Rcc in seeds and seedlings by real-time PCR (qPCR), (ii) to determine the importance of seeds as a source of in-crop Rcc inoculum in production systems in Uruguay, (iii) to develop a methodology to determine the fungicides proposed for the control of rhamulariosis in barley grain, and (iv) to identify foliar fungicide application strategies to minimise rhamulariosis and ensure fungicide safety in the grain produced. The qPCR technique was validated for the detection and quantification of Rcc in barley seeds and seedlings. This qPCR technique will allow the optimal timing of foliar fungicide applications to be determined by detecting Rcc in seedlings. The amount of Rcc DNA in commercial lots varied within and between growing seasons, highlighting the importance of this tool for quantifying fungal load prior to sowing. A method was developed to quantify fungicide residues in barley grain. This method was extended to quantify fungicides in wheat grain and mycotoxins produced by the Fusarium species. This analytical methodology could be useful for monitoring compliance with maximum residue limits (MRLs) in winter cereal production. Foliar fungicide strategies for the control of RLS were evaluated in five trials over three consecutive years. The efficacy of fungicides in controlling the disease and ensuring grain safety was tested with fungicide residue levels below MRLs. The results contribute to the management of RLS with tools to reduce fungicide use and ensure barley grain safety.