Developing a rationale to integrate take-all control measures, reduce disease impact and maximise wheat margins

Abstract

• This project undertook an epidemiological assessment of existing take-all data provided by ADAS (UK) and INRA (France) for consecutive epidemics of take-all in a sequence of winter wheat crops. From the analysis of these data we outlined an epidemiological model for take-all decline.
• Analysis of the ADAS data provided insight into changes in the magnitude of infection and disease suppression of take-all during a sequence of wheat crops. First wheat crops were characterised by low levels of primary (infectious crop debris to root) and secondary (infectious root to healthy root) infection, and there was no detectable disease suppression. This meant that at the time of crop harvest, disease was still progressing rapidly, but from a low starting point. For second, third and forth wheat crops, a significant increase in primary infection, secondary infection and disease suppression was detected. This was followed in subsequent crops by a reduction to intermediate levels of secondary infection and disease suppression in fifth and seventh crops. Silthiofam seed treatment marginally, but not significantly, delayed the onset of take-all decline.
• Spatial analysis of the INRA data detected average disease patches measuring 0.5 - 1.0 m in diameter. These patches can aggregate into the larger patches of disease which growers are familiar with.  Patches did not increase in size during the course of the epidemic but a significant increase in the severity of disease was detected, which makes patches more noticeable visually. We conclude that the spatial structure of an epidemic is predetermined at the root level by primary infection, reflecting changes in inoculum that are affected by cultivation and management practice during the inter-cropping period.
• These analyses were used to compile a theory for the spatio-temporal dynamics of take-all decline from which the outline of an epidemiological model was developed. The model includes terms for host dynamics (root production), pathogen dynamics (primary infection, secondary infection, inoculum production and inoculum decay) and antagonist dynamics during the within-crop and inter-crop periods accounting for epidemics over a sequence of successive wheat crops. Initial simulations show clearly that a rise and fall in disease severity, characteristic of take-all decline, can only be obtained when the antagonist population reduces the rate of disease transmission.  This new analysis can be used to explore combinations of potential control measures to identify those which are sufficiently promising to justify testing, and help define experimental designs, important variates and sampling procedures to improve efficiency of research.