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Subject: Fungal diseases of plants.

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    Identification of Quantitative Trait Loci for Resistance to Tan Spot in Durum Wheat
    (North Dakota State University, 2018) Galagedara, Nelomie Nayanathara
    Tan spot, caused by Pyrenophora tritici-repentis (Ptr), is a major foliar disease on wheat. The pathosystem involves three pairs of necrotrophic effector (NE) and host sensitivity (S) gene interactions, namely Ptr ToxA-Tsn1, Ptr ToxB-Tsc2 and Ptr ToxC-Tsc1. Additionally, genetic factors conferring race-nonspecific resistance have been identified. The objectives of this study were to map tan spot resistance QTL and investigate the role of NE-S interactions in disease in durum using association and bi-parental mapping. Evaluation of a worldwide collection of durum accessions allowed identifying highly resistant nineteen lines to multiple Ptr races. Association mapping revealed genomic regions on chromosomes 1A, 2B and 3B significantly associated with resistance to tan spot, which likely correspond to Tsc1, Tsc2 and racenonspecific resistance. Using a bi-parental population derived from Ben and PI 41025, we found that ToxA-Tsn1 interaction plays no significant role in disease, instead a major race-nonspecific QTL on chromosome 5A was identified.
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    Revisiting Management Practices for Diseases of Spring Barley in North Dakota
    (North Dakota State University, 2018) Schuh, Casey Steven
    Common barley diseases observed in North Dakota include net blotch, spot blotch, leaf and stripe rust, bacterial leaf streak, and Fusarium head blight. The first objective of this research was to determine the effect of variety and fungicide timing on disease development of barley under conventionally tilled systems. Five field trials were performed in 2016-2017 to test the effect of common varieties and fungicide applications on foliar disease of barley. Overall, varietal selection had a greater effect on the level of foliar disease observed than fungicide application. The second objective focused on the efficacy and timing of adepidyn and prothioconazole + tebuconazole on Fusarium head blight. An inoculated greenhouse experiment was performed the fall of 2017 to determine the effectiveness of fungicide timing at half-spike, full-spike, and five days after full-spike. The protectant capabilities of the fungicides were greater than their curative properties.