USE OF A SELECTIVE MEDIUM FOR ISOLATION OF STAGONOSPORA-NODORUM FROM BARLEY SEED

We developed a selective medium designated SNAB (Stagonospora nodorum agar for barley) to improve the isolation of the barley biotype of S. nodorum from barley seed and to improve the accuracy of seed assays. The medium contains (per liter of deionized water) Difco potatodextrose agar (10 g), Bacto Peptone (2 g), oxgall (1.5 g), agar (12 g), chloroneb (5 mg), cupric hydroxide (10 mg), dichloran (7.5 mg) dissolved in 20% ethanol, and CGA-449 50 WS (CIBA-GEIGY Corp.) (1 mg). It also contains chloramphenicol (3.13 mg), erythromycin (3.13 mg), tetracycline hydrochloride (12.5 mg) dissolved in 20% ethanol, neomycin sulfate (10 mg), which suppresses bacteria, and paraquat (67-mu-l at 29% a.i.), which reduces seed germination. Seeds were surface-sterilized and then incubated on SNAB or oxgall agar at 20 C with a 12-h photoperiod for 12 days. Recovery of the barley and wheat biotypes of S. nodorum was significantly higher on SNAB than on oxgall agar. Both biotypes sporulated on SNAB but not on oxgall agar. Isolation of the barley biotype was improved after seed was stored for 6 mo, probably because of a decline in other seed fungi. Both biotypes were isolated from barley seed from Maryland and North Carolina, but only the wheat biotype was isolated from seed from Arkansas. Both biotypes sporulated on and were isolated from the lemma, palea, and pericarp. Both biotypes were recovered from glumes approximately twice as often as from the caryopsis.