Evaluation of Pyrenophora tritici-repentis Infection of Wheat Heads

Pao Theen See,Nikki Schultz,Caroline S Moffat

doi:10.3390/agriculture10090417

Abstract

The incidence of wheat head infection by Pyrenophora tritici-repentis (Ptr), the etiological agent of tan spot disease, was evaluated during grain development in a glasshouse experiment. Heads artificially inoculated with a Ptr spore suspension developed widespread brown spots across the spikelets, and mycelia and conidophores were observed on glumes and awns. Seeds of heavily infected heads were darkened and shrivelled, but no red smudge symptoms were apparent. The recovery rate of Ptr isolates from the inoculated wheat heads was low, and colonies that were re-isolated displayed an irregular morphology with reddish mycelia when grown on agar plates. The presence of Ptr on inoculated wheat heads was assessed directly via PCR detection, and a limitation of Ptr hyphae to proliferate beyond the point of contact of spore inoculum on floret tissues was observed. The systemic transmission of Ptr from infected seeds was minimal; however, saprophytic growth of the pathogen occurred on the senescing leaves of wheat plants grown from inoculated seeds. Thus, even though Ptr seed infection is not as common as foliar infection, infected seeds are still a source of disease inoculum and screening for pathogen contamination is advisable.

Highlights

The major wheat disease tan spot is caused by the fungus Pyrenophora tritici-repentis (Died.)abbreviated to Ptr
Wheat heads inoculated with Ptr developed small brown spots that were visible on the entire spikelet (Figure 1A–D)
Symptoms of Ptr infection on wheat heads were distinct from the typical foliar symptoms of tan spot, with brown spots present on the spikelets

Summary

Introduction

The major wheat disease tan spot is caused by the fungus Pyrenophora tritici-repentis (Died.)abbreviated to Ptr. The most common symptom associated with seed infection by Ptr is red smudge, a pink to bright red discolouration of the wheat kernel [1,5]. Other seed symptoms have been reported to be associated with Ptr infection and include black point [1], a black discolouration of the grain coat overlying the germ, and dark smudge, which is characterised by darkening at the germ end [5,6]; other fungal pathogens such as Alternaria species and Cochiliobolus sativus are generally associated with such darkening symptoms [1,3,7,8]. In Australia, grain staining limits are a maximum of 5% for high protein milling grades and up to 50% for feed wheat, while pink fungal staining limits are 2% for milling wheat and 5% for general purpose and feed grades [10]

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