INHERITANCE OF SEPTORIA-GLUME BLOTCH RESISTANCE IN WHEAT

Incorporation of resistance to septoria glume blotch, caused by Stagon ospora nodorum (Berk.) Castellani & E.G. Germano, into wheat (Triticum aestivum L.) is complex because resistance is quantitatively inherite d. The Brazilian wheat 'Cotipora' expresses a high level of resistance to this pathogen. Crosses were made between Cotipora and the suscepti ble Purdue line, M1791A1-1-6. Populations of parents, F1, F2, BCF1, an d BCF, were inoculated with a conidial suspension of the pathogen cont aining 2.5 x 10(6) spores mL-1 and given a moist period of 52 h. Perce ntage of diseased tissue was estimated on the spikes and flag leaves f our times over a 20-d period, and an area under disease progress curve (AUDPC) was calculated. Correlations between AUDPCs of spike and flag leaf in the F2 and BCF1 populations were 0.312 and 0.283, respectivel y, indicating that resistance is at least partially controlled by diff erent genes in these two plant organs. Resistance was partially domina nt in the F1 generation in both the spike and flag leaf. In the F2, BC F1, and BCF, generations, however, dominant gene action was not eviden t. The gene number estimate for the spike reaction was 3.16. Broad sen se heritability estimates were 0.51 and 0.34 for the spike and flag le af reactions to S. nodorum, respectively. Cotipora is a valuable sourc e of S. nodorum resistance because of its high level of resistance exp ressed in the spike and flag leaves.