The importance of asymptomatic infection in sustainable crop protection

Scald or Rhynchosporium, caused by the fungus Rhynchosporium commune, is difficult to control with fungicides and severe epidemics may appear suddenly. Its epidemiology is not well understood as it is based on disease symptoms rather than the presence of the pathogen. Quantitative PCR enables detection and quantification of pathogen DNA in barley plants in both presymptomatic phases of infection and where they remain asymptomatic throughout their life cycle. Seed-borne inoculum was identified as a significant source for early infection of barley crops, with substantial amounts of R. commune DNA found in crops from infected seed but severity of seed infection correlated poorly with amounts of pathogen DNA (leaves), disease severity (leaves) and yield loss later in the cropping season. R. commune can colonise barley crops extensively throughout the cropping season (from seed to seed) in the absence of visual symptoms which has implications for the use of fungicides, breeding programmes and national variety recommended lists. The genetic basis of several different components of resistance to R. Commune in barley was investigated in a mapping population derived from a winter x spring barley cross. Relative expression of symptoms quantified using the residual values from a linear regression of amount of R. Commune DNA against visual plot disease score and was generally highly correlated. A QTL on chromosome 7H was identified as having a significant effect on the expression of visual disease symptoms relative to overall amount of R. commune colonisation.Non peer reviewe

Resistance to Rhynchosporium secalis in a cross between winter and spring barley

Winter barley types shows higher levels of field resistance to R. secalis compared to spring barley varieties. In addition, barley leaves have been shown to tolerate relatively high levels of R. secalis colonisation in the absence of visible symptoms, suggesting that suppression of symptom expression may be an alternative mechanism of resistance. This study examined resistance in 191 DH lines from a cross between spring variety Cocktail, and a winter parent derived from a cross between Leonie and Pearl. Field resistance was scored by measuring visible symptoms and also by R. secalis specific qPCR of sampled leaves. Two novel resistance QTL (on chromosomes 2H and 7H) were identified, which affected both pathogen colonisation and visible symptoms. These were not associated with genes controlling winter/spring growth habit. A further QTL (on chromosome 5H) was identified as affecting relative expression of disease symptomsNon peer reviewe

Role of inoculum sources in Rhynchosporium population dynamics and epidemics on barley.

This is the final report of a 48 month project (RD-2004-3099) which started in March 2006. It was a Sustainable Arable LINK project funded by a contract for £392,077 from BBSRC with in-kind contributions from HGCA, Du Pont UK, Masstock Arable, KWS UK and Scottish Agronomy.Rhynchosporium leaf blotch of barley, caused by the fungus Rhynchosporium secalis, is of increasing importance in world agriculture. It is the most serious disease of winter and spring barley in the UK, causing substantial losses nationally, despite expenditure of £50M per year on fungicides. The disease is difficult to control with fungicides and severe epidemics may appear suddenly. The sources of inoculum responsible for starting such epidemics are not well understood