Quantifying Infection of Wheat by Races of Pyrenophora tritici-repentis Producing Different Host-Selective Toxins

• Author / Creator

  Ma, Xinyi

• Pyrenophora tritici-repentis, the cause of tan spot of wheat, produces several host-selective toxins (HSTs), including Ptr ToxA and Ptr ToxB. Ptr ToxA-producing isolates are predominant in Canada, while Ptr ToxB-producing isolates are extremely rare. The reason for the scarcity of ToxB+ isolates is not clear, since about a quarter of current and historical Canadian wheat genotypes are sensitive to Ptr ToxB. Experiments were undertaken to determine if ToxA+ isolates can outcompete ToxB+ isolates when they occur together on wheat sensitive to both HSTs. Four wheat genotypes including ‘Katepwa’ (sensitive to Ptr ToxA and Ptr ToxB) were inoculated with isolates 86-124 (ToxA+), Ptf3 (ToxA+, ToxB+), Alg3-24 (ToxB+) and 90-2 (avirulent, no HSTs produced) of P. tritici-repentis, alone or in various combinations. The most severe tan spot symptoms were observed after inoculation of ‘Katepwa’ with 86-124 or Ptf3, followed by Alg3-24. Inoculation with 90-2 produced few if any symptoms. Symptom severity was reduced when 86-124 was co-inoculated with Alg3-24 or 90-2, or when Alg3-24 was co-inoculated with 90-2. Fluorescence microcopy analysis indicated more extensive colonization of inoculated leaf tissue by 86-124 and Ptf3 than by Alg3-24 at 120 hours post-inoculation. The avirulent isolate 90-2 rarely penetrated the leaves. Quantitative PCR analysis with isolate-specific probes and primers, and with an isolate-non-specific probe and primer set, also suggested significantly greater proliferation of 86-124 and Ptf3 than Alg3-24 in inoculated leaf tissue. Collectively, the results indicate that ToxA+ isolates may outcompete ToxB+ isolates, likely contributing to their greater prevalence in Canada.

• Subjects / Keywords

  • Ptr ToxA
  • Ptr ToxB
  • Pyrenophora tritici-repentis
  • Tan spot

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R34B2XM6F

• License

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