VIRULENCE SPECTRUM TO BARLEY HORDEUM VULGARE L IN SOME ISOLATES OF COCHLIOBOLUS SATIVUS FROM SYRIA
M.I.E. Arabi, M. Jawhar
Isolates of Cochliobolus sativus (Ito and Kurib) Drechsl. ex Dast.[anamorph, Bipolaris sorokiniana (Sacc. in Sorok.)] that cause common root rot (CRR) symptoms on barley (Hordeum vulgare L.) were collected in 1998 and 1999 from fields in different regions of Syria. Their virulence spectra were determined using 11 barley cultivars. Cultivars exhibited a continuous range of response from very susceptible to moderately resistant but none was immune from the disease. A cluster analysis indicated that the isolates exhibited distinct differential virulence patterns with three groups. Mean disease rating of 4.37 was the separation point between avirulent and virulent reactions. Isolate CRR16 had the highest mean virulence with lowest variance across all cultivars; and thus it was proposed to be considered as a physiological race. To incorporate adequate levels of resistance into future barley cultivars, disease evaluations should be made with Cochliobolus sativus isolates that express the full spectrum of virulence found in Syria.