A DIFFERENTIAL MEDIUM FOR DISCRIMINATING BETWEEN DRECHSLERA BROMI (DIED.) SHOEMAKER AND D. TRITICI-REPENTIS (DIED.) SHOEMAKER

Abstract

Drecheslera tritici-repentis (Dtr) causes tan spot, one of the important leaf diseases of wheat worldwide. The fungus has a broad host range and causes leaf spots on many members of family Poaceae including smooth bromegrass. Drechslera bromi (Db), causes brown leaf spotonsmoothgrass. Dtr isolates have been grouped into eight races based on their ability to induce two distinct symptoms, necrosis and chlorosis, on appropriate wheat differential genotypes. Of these eight races, race 4 and Db induce either symptom except small pinhead size black spots on tan spot differential lines. Dtr and Db are morphologically very similar and are difficult to discriminate between the two species. Db isolates can be characterized as race 4 while Dtr isolates recovered from bromegrass are race characterized because both are avirulent on the tan spot wheat differential genotypes. It is imperative to develop a culture medium that could distinguish these two species and avoid the chances of mischaracterization of Db isolates as Dtr race 4. In this study, we evaluated V8PDA (V-8 juice potato dextrose agar) medium, a routinely medium used to grow Dtr and Db for spore production, as a differential medium. Forty-single-spore isolates each of Db and Dtr were grown on V8PDA plates and slants. Colony growth diameter and presence or absence of protothecia data of each isolate were recorded after 6 and 13 days for cultures grown in plates and after 10 and 13 days for cultures grown in slants. All Db isolates identity was confirmed by inoculating them individually on seven brown spot susceptible smooth bromegrass cultivars. All Db isolates grew slower with average colony diameter 2.5 cm than Dtr with average colony diameter 5 cm. Also, all Db but not Dtr isolates developed protothecia in cultures both in plates and in slants. Based on our results, we recommend V8PDA medium as a differential medium for discriminating between Dtrand D. bromi.