Cocksfoot (Dactylis glomerata) is a pasture species with significant economic and ecological value in temperate regions. It is an important grazing crop in New Zealand to support meat and dairy production. In 2018, cocksfoot downy mildew was identified as an emerging threat to cocksfoot seed production, particularly in the Canterbury region of New Zealand. The disease is characterised by symptoms such as seed head bleaching, chlorosis and reduced yield and quality of seeds. The causal agent has been tentatively identified as Sclerophthora cryophila based on spore morphology. Partial DNA sequencing has confirmed the organism is an oomycete, but phylogenetic analysis will be required to determine its position within the downy mildews. Further research on its biology and epidemiology is currently underway.
This study investigated the influence of temperature on sporangia formation, zoospore release and spore morphology of the cocksfoot downy mildew pathogen. Symptomatic tissues were floated on water to induce sporulation and incubated under different temperatures (4°C, 9°C, 14°C, 19°C, 24°C). Sporangia which remained attached to the tissue were collected using a cellotape strip and placed onto a microscope slide, whilst zoospores and sporangia which detached into the surrounding water were counted using a haemocytometer. The results showed that the lower temperature (4°C) was beneficial for the formation of sporangia and sustained sporulation, suggesting an adaptation to cold environments. In contrast, slightly higher temperatures (9°C, 14°C) promoted zoospore release, with zoospores tending to encyst more rapidly under these conditions. Investigation of the effect of temperature on sporangia attachment revealed that detachment was more prominent at 19°C and 24°C, whereas sporangia remained predominantly attached at 4°C, suggesting higher temperatures may promote sporangia detachment. These findings provide insights into the biology and epidemiology of cocksfoot downy mildew, supporting further research and the potential for development of effective disease management strategies in cocksfoot seed crops.