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New Zealand Plant Protection 68 (2015): 449

Distribution of Pyrenophora tritici-repentis, the causal fungus of tan spot, in the South Island

S.K. Weith, H.J. Ridgway, I.C. Harvey, R.A. Craigie and E.E. Jones


Tan spot of wheat is caused by the fungus Pyrenophora tritici-repentis (Ptr) with reported incidence in New Zealand increasing in recent years. Lesions characteristic of Ptr infection, being oval tan spots surrounded by a chlorotic halo, were observed on wheat leaves in 15 different wheat paddocks throughout the South Island in the 2013-14 season. Fungal isolates recovered from these lesions on potato dextrose agar produced grey-green fluffy mycelium characteristic of Ptr. Species-specific PCR using published primers (PtrUniqueF2/ PtrUniqueR2) generated a PCR product of 490 bp, diagnostic of Ptr. Sequencing of the rDNA and β-tubulin gene regions confirmed the identification. Ptr was found to be widely distributed throughout the wheat growing areas in the South Island from Southland to North Canterbury. A post-harvest farmer questionnaire was also undertaken. Questionnaire answers revealed that continuous sowing of untreated wheat seed, conservative tillage and low rate applications of fungicides may have exacerbated the severity of tan spot outbreaks during the 2013-14 season. Further work to identify susceptible wheat cultivars and sensitivity to fungicides is currently under way.

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