Distribution of <i>Pyrenophora triticirepentis</i> the causal fungus of tan spot in the South Island

Abstract

Tan spot of wheat is caused by the fungus Pyrenophora triticirepentis (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 201314 season Fungal isolates recovered from these lesions on potato dextrose agar produced greygreen fluffy mycelium characteristic of Ptr Speciesspecific PCR using published primers (PtrUniqueF2/ PtrUniqueR2) generated a PCR product of 490 bp diagnostic of Ptr Sequencing of the rDNA and 946;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 postharvest 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 201314 season Further work to identify susceptible wheat cultivars and sensitivity to fungicides is currently under way