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During the inspection of imported sweet corn (Zea mays), a specimen with dry rot symptoms was detected by Ministry for Primary Industries quarantine officers. A sample was sent to the MPI Plant Health and Environment Laboratory for diagnostics, and initial examination found a layer of yeast cells on the surface of the symptomatic tissue. The fungus was cultured and identified based on DNA sequences as Ustilago maydis. While the corn-smut pathogen U. maydis is well known to cause tumour like galls on corn kernels, it is a less recognised fact that this fungus can also grow as a yeast. To determine if the yeast stage could have been associated with the dry-rot symptoms observed on the specimen, healthy material was inoculated with the isolated U. maydis strain. No symptoms developed on inoculated material, indicating that the yeast cells were likely multiplying on the surface of the cut corn ear as saprobes. To our knowledge, this is the first report of U. maydis yeast stage on corn ears and indicates a previously unconsidered pathway for the organism. For the yeast stage to cause disease, mating with a compatible mating type on the surface of a living host plant would be required.

A project aiming to enhance biosecurity and market access in the Pacific was launched by NZ Aid in 2016. The project intends to benefit the economies of New Zealand’s Pacific neighbours by improving their biosecurity systems which, in turn, would help to protect New Zealand’s borders. Under the current project, the MPI’s Plant Health and Environment Laboratory (PHEL) is accountable for delivering insect pest and disease diagnostic training in the Pacific and developing diagnostic tools. The PHEL Mycology and Bacteriology team has delivered a number of plant pathology training sessions in New Zealand, Cook Islands and Fiji. The main focus of the pathology module was to provide the Biosecurity Authority of Fiji (BAF) Plant Health Laboratory staff with skills and tools to conduct plant disease diagnostics at their facility. This included a full laboratory refurbishment and new molecular setup. As a result, the BAF team has become efficient with isolating and identifying plant pathogens using a combination of morphology and DNA-based approaches. They are now able to provide fast and sensitive testing for high impact diseases at the border or in future incursions. In addition to laboratory staff training, a number of quarantine officers were trained to enable them to recognise diseased plant material during import and export fresh produce inspections.

The Mycology and Bacteriology team of the Ministry for Primary Industries’ Plant Health and Environment Laboratory is responsible for the identification and verification of all suspected exotic, new, and emerging pathogens affecting plants and the environment in New Zealand. We work in an applied diagnostic environment where results can have significant implications for biosecurity. Sample submissions often result in detection of new to New Zealand fungi and bacteria on plants for which information on fungal and bacterial associations is generally sparse. The complexity of testing required is quite varied with samples being submitted from post entry quarantine (looking for a known pathogen using specific tests), border or surveillance (unknown pathogens requiring multiple tests), or a biosecurity response (scaling up to test large numbers, identification resolution required to strain level). Applied test methods depend largely on the sample type and consist of morphological identification, biochemical testing, pathogenicity testing, serological and molecular techniques, including high throughput sequencing. A profile of our diagnostic work and the most commonly detected taxa and host associations are presented.