Evaluation of NDSU Hard Red Winter Wheat Germplasm for Broad Based Resistance to Tan Spot and Septoria Nodorum Blotch.

Tan spot and Septoria nodorum blotch (caused by Pyrenophora tritici-repentis and Parastagonospora nodorum, respectively) are destructive necrotrophic fungal parasites of wheat. Resistance to both diseases is quantitative and complex due to the action of multiple necrotrophic effectors which facilitate disease development in susceptible hosts. Multiple effectors of each fungus have been characterized. In each case susceptible wheat host plants possess a dominant allele for sensitivity to the particular effector. Winter wheat varieties grown in North Dakota generally lack resistance to the two diseases. In order to identify resistant winter wheat genotypes for use in breeding, two sets of material are being studied. Firstly, a group of 164 inbred lines consisting of advanced NDSU HRWW breeding lines (133), current and exotic winter wheat varieties (16), HRSW (5), HRS X synthetic wheat derivatives (7), and tritipyrums (3). The second group includes 594 F₄ families derived from a recurrent mass selection base population with 109 HRWW and HRSW founder parents. The two populations were inoculated and screened for resistance to tan spot isolate Pti-2 and P. nodorum isolate Sn4. In addition, the first group was characterized for sensitivity to four necrotrophic effectors (Ptr ToxA, Ptr ToxB, SnTox1, and SnTox3). Twenty-eight of the 164 lines exhibited resistance to either fungus with five showing resistance to both. Among 10 Sn4 resistant lines, effector insensitivity distribution was 50%, 80%, 70%, and 80% whereas the 18 Pti-2 resistant lines were 61%, 83%, 61%, and 67%. In the F₄ population, thirteen lines showed promising tan spot resistance, 20 had P. nodorum resistance, and a few had resistance to both diseases. The selected plants are being grown and their progeny will be tested more extensively in a replicated trial involving a broader spectrum of isolates and effectors.