INHERITANCE OF SEPTORIA-GLUME BLOTCH RESISTANCE IN WHEAT

Incorporation of resistance to septoria glume blotch, caused by Stagonospora nodorum (Berk.) Castellani & E.G. Germano, into wheat (Triticum aestivum L.) is complex because resistance is quantitatively inherited. The Brazilian wheat 'Cotipora' expresses a high level of resistance to this pathogen. Crosses were made between Cotipora and the susceptible Purdue line, M1791A1-1-6. Populations of parents, F1, F2, BCF1, and BCF, were inoculated with a conidial suspension of the pathogen containing 2.5 x 10(6) spores mL-1 and given a moist period of 52 h. Percentage of diseased tissue was estimated on the spikes and flag leaves four 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, respectively, indicating that resistance is at least partially controlled by different genes in these two plant organs. Resistance was partially dominant in the F1 generation in both the spike and flag leaf. In the F2, BCF1, and BCF, generations, however, dominant gene action was not evident. The gene number estimate for the spike reaction was 3.16. Broad sense heritability estimates were 0.51 and 0.34 for the spike and flag leaf reactions to S. nodorum, respectively. Cotipora is a valuable source of S. nodorum resistance because of its high level of resistance expressed in the spike and flag leaves.