Monitoring growth of Bipolaris sorokiniana in plant tissue using GUS (β-glucuronidase) as a marker

Abstract

The phytotoxin producing fungus Bipolaris sorokiniana is a severe pathogen on barley and other cereals and may infect above ground as well as below ground tissues of the host plant. Host resistance to B. sorokiniana varies quantitatively among different cultivars. No total resistance occurs but it appears that relatively resistant cultivars can resist fungal development better within the host tissue, but not stop fungal penetration. Ecological studies on the infection of plants, especially in the rhizosphere are few, mainly due to a lack of suitable detection and quantification methods. Biomarkers, e.g. ergosterol, have been used for monitoring unspecific fungi. For studies of a particular fungus a more specific marker would be desirable. Methods to transform fungi offer possibilities to introduce markers that can later be monitored. I have successfully transformed a marker gene (GUS, β-glucuronidase from E. coli) into a strain of B. sorokiniana (Liljeroth et al., 1993) which makes it possible to quantify fungal growth in infected plant tissue. However, to be able to get reliable results from experimental studies, knowledge of the stability of the transformant, the variation in specific expression of the marker gene and the correlation with other recognized methods is necessary. This paper deals with these questions and also with measurements of fungal growth in root tissue of barley and other cereals in relation to root characters such as resistance and root cortical cell death.