Use of specific differential isolates of Rhynchosporium commune to detect minor gene resistance to leaf scald in barley seedlings

Major gene resistance to leaf scald caused by Rhynchosporium commune is readily detected in barley seedlings. Screening of barley lines in this manner has been used to identify and map the presence of several such major genes. Similar detection systems have not been possible for minor genes, detection of which has come from field evaluation of plants at later growth stages. Resistance contributed by such minor genes has often therefore been termed adult plant resistance (APR) and most barley lines possess some degree of such resistance to scald. The presence and genetic control of minor gene resistance has been more difficult to study due to the requirement for field screening and the partial and apparent multigenic nature of this resistance. In this paper we report the identification of isolates of R. commune and methods which enable the presence of minor genes to be detected at the seedling stage in some key Australian varieties and breeding parents. A mapping population has been used to confirm that the QTL detected in seedlings and in the field are the same.