The ability of barley powdery mildew to grow in vitro

A technique was developed for the in vitro culture of Blumeria graminis f. sp. hordei, an obligate biotrophic pathogen of barley. Optimal growth occurred at pH 5.6 on a medium containing 39 gl(-1) potato dextrose agar, 40 gl(-1) shredded fresh barley leaves, 20 gl(-1) sucrose, 13 mgl(-1) kanamycin and 80 mgl(-1) benzimidazole. At 20degreesC (90% relative humidity), conidia germinated 48 h after inoculation, producing an average colony diameter of I cm after 10 days. However, numerous colonies were present on the medium after 15 days. Light microscopy showed that there was a positive relationship between the amount of leaf in the medium and fungus growth. The fungus retained its virulence during 60 days of storage in vitro, and was able to infect barley. This is a useful and novel technique that could be beneficial in barley pathology breeding programs.