The importance and control of stem-base diseases of cereals

Summary

Sector:
Cereals & Oilseeds
Project code:
PR176
Date:
01 September 1992 - 31 August 1996
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£486,644 From HGCA (Project No. 0015/1/91)
Project leader:
D J Royle IACR-Long Ashton Research Station, Dept of Agricultural Sciences, University of Bristol, Long Ashton, Bristol BS18 9AF

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pr176-final-project-report

About this project

Abstract

Eyespot

1. Immunodiagnostics, used to chart eyespot epidemics in different wheat cultivars over a four-year period, confirmed that diagnostic kits provide a simple, robust and reproducible way to monitor progress of this disease quantitatively.

2. Eyespot antigen levels varied between cultivars but once eyespot symptoms appeared, antigen levels correlated well with the disease levels assessed visually. Antigen levels provided a better measure of eyespot severity than visual assessment and exposed variation in factors affecting eyespot development which were not apparent from the visual assessments.

3. Immunodiagnostics detected eyespot before symptoms appeared. Antigen levels in the eyespot-resistant Rendezvous were often similar or even greater than in susceptible cultivars. Resistance to eyespot in Rendezvous appears to be expressed not by blocking infection, but by delaying and suppressing symptom expression.

4. Throughout the field experiments at IACR-Long Ashton and NIAB, uninoculated plots had high levels of eyespot, even in first wheats, indicating that the eyespot pathogen is considerably more mobile than was previously thought. Wind-blown ascospores of the recently-discovered sexual stage, Tapesia yallundae, may initiate eyespot and explain the widespread and uniform distribution of antigen units throughout the crops. First-wheat crops, previously considered to be of low risk from eyespot attack, therefore need to be monitored carefully, and where early infections are detected in susceptible cultivars, fungicides should be applied.

5. As a consequence of the occurrence of eyespot in uninoculated plots, attempts to manipulate eyespot levels in the Long Ashton experiments was only partially successful. Although the Rye (R)-pathotype dominated in plots inoculated with either the R- or the Wheat (W)-pathotype, the W-pathotype appeared to be more invasive and damaged crops earlier than the R-pathotype.

6. Correlations between antigen levels and either final disease levels or yield were erratic and dependent on cultivar. Occasionally, antigen levels at GS24-39 were related to yield loss and a threshold level of disease could be suggested. However, this was not normally the case and no obvious spray threshold based on either visually-determined symptoms or antigen levels could be proposed.

7. The experiments at NIAB showed that symptoms produced by both W- and R- pathotypes can become severe by the time of grain-filling. However, a given level of symptoms caused by R-type eyespot may be less damaging to yield than the same level caused by W-type eyespot. The implication is that eyespot-related yield losses may be lower today, with an eyespot population dominated by the R-type, than they were before 1980, when the population was almost entirely W-type. Diseaselyield loss relationships derived from W-type eyespot need re-defining for R-type.

8. In some cases of severe eyespot, there may be little or no response to eyespot control by fungicides. This underlines the difficulty of predicting whether fungicide application is likely to be cost-effective.

9. Cultivars rank similarly for resistance to eyespot, whether infection is caused by W- or R-type. A single rating should be adequate to describe a cultivar's resistance to either pathotype and a grower does not need to be aware of the composition of the eyespot population in a field before choosing a suitable cultivar.

10. The resistance of cultivars to W-type infection, as indicated by DNA-diagnostics, was in close agreement with symptom expression. However, PCR detected higher levels of R- type eyespot in the two most resistant cultivars than would have been expected by their low symptom expression. PCR also detected R-type eyespot in all cultivars in sprayed plots which were without symptoms.

11. In the experiments described in section 1.3 DNA-diagnostics appeared to be able to confirm with reasonable accuracy the presence of pre-symptomatic eyespot and to quantify W- and R-type infections. However, there is still no accurate, early-disease threshold upon which to predict the degree of risk for individual crops.

12. Overall, prochloraz gave better yield maintenance, associated with reductions in the eyespot index and, where it occurred, lodging, compared to flusilazole and cyprodinil.

13. The optimum time for a single treatment varied markedly across the 14 site/year combinations studied. At some sites, especially Markle Mains, (the same location for four years), it was possible to distinguish the mid-tiller (GS23-27) stage and the first node (GS31) as the best times for fungicide application, numerically but not statistically. This was possible at none of the other sites. At Markle Mains, the optimum times for a split treatment were early tillering (GS23-25), then up to first node (GS20-3 1) but not GS30 nor GS32. The best timing for application of prochloraz thus remains uncertain.

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