Growth of races 38 and 17, Puccinia graminis f. sp. tritici, on artificial media

Abstract

Isolates of races 38 and 17, Puccinia graminis f. sp. tritici, which had grown poorly in earlier trials on 0.1% peptone media, were grown successfully on media containing higher concentrations of peptone combined with an acid hydrolysate of casein. Race 38 grew consistently on media containing 0.4% peptone and 0.4–0.8% casein hydrolysate in a procedure in which 1–3 mg of uredospores were seeded on 15 ml agar medium in 85-mm-diam petri dishes. Race 17 grew less consistently than race 38 did, but its consistency was improved by reducing dish diameter to 43 mm and agar volume to 3 ml and increasing the inoculum mass to 5–10 mg/dish. Other modifications in procedure and in media composition failed to improve growth of race 17 from uredospores. In serial monthly subculturings, race 38 achieved stable growth rates (exceeding 40 μm increase in colony diameter per day) by the 2nd month after a culture had originated from spore seedings. Race 17 grew poorly in serial subculturings, except for one culture which began to grow well after a year of extremely slow growth. The results indicate that a wider range of isolates of P. graminis f. sp. tritici can be grown on enriched media than was possible earlier but that routine, rapid culture of some isolates is not yet possible.